Subsections of Containers

Containers

Introduction to Containers

  • Take advantage of the native virtualization features available in the Linux kernel.
  • Each container typically encapsulates one self-contained application that includes all dependencies such as library files, configuration files, software binaries, and services.

Traditional server/ application deployment:

  • Applications may have conflicting requirements in terms of shared library files, package dependencies, and software versioning.
  • Patching or updating the operating system may result in breaking an application functionality.
  • Developers perform an analysis on their current deployments before they decide whether to collocate a new application with an existing one or to go with a new server without taking the risk of breaking the current operation.

Container Model:

  • Developers can now package their application alongside dependencies, shared library files, environment variables, and other specifics in a single image file and use that file to run the application in a unique, isolated “environment” called container.

  • A container is essentially a set of processes that runs in complete seclusion on a Linux system.

  • A single Linux system running on bare metal hardware or in a virtual machine may have tens or hundreds of containers running at a time.

  • The underlying hardware may be located either on the ground or in the cloud.

  • Each container is treated as a complete whole, which can be tagged, started, stopped, restarted, or even transported to another server without impacting other running containers.

  • Any conflicts that may exist among applications, within application components, or with the operating system can be evaded.

  • Applications encapsulated to run inside containers are called containerized applications.

  • Containerization is a growing trend for architecting and deploying applications, application components, and databases in real world environments.

Containers and the Linux Features

  • Container technology employs some of the core features available in the Linux kernel.
  • These features include:
    • control groups
    • namespaces
    • seccomp (secure computing mode)
    • SELinux

Control Groups (cgroups)

  • Split processes into groups to set limits on their consumption of compute resources—CPU, memory, disk, and network I/O.
  • These restrictions result in controlling individual processes from over utilizing available resources.

Namespaces

  • Restrict the ability of process groups from seeing or accessing system resources—PIDs, network interfaces, mount points, hostname, etc.
  • Creates a layer of isolation between process groups and the rest of the system.
  • Guarantees a secure, performant, and stable environment for containerized applications as well as the host operating system.

Secure Computing Mode (seccomp) and SELinux

  • Impose security constraints thereby protecting processes from one another and the host operating system from running processes.
  • Container technology employs these characteristics to run processes isolated in a highly secure environment with full control over what they can or cannot do.

Benefits of Using Containers

Isolation

  • Containers are not affected due to changes in the host operating system or in other hosted or containerized applications, as they run fully isolated from the rest of the environment.

Loose Coupling

  • Containerized applications are loosely coupled with the underlying operating system due to their self-containment and minimal level of dependency.

Maintenance Independence

  • Maintenance is performed independently on individual containers.

Less Overhead

  • Containers require fewer system resources than do bare metal and virtual servers.

Transition Time

  • Containers require a few seconds to start and stop.

Transition Independence

  • Transitioning from one state to another (start or stop) is independent of other containers, and it does not affect or require a restart of any underlying host operating system service.

Portability

  • Containers can be migrated to other servers without modifications to the contained applications.
  • Target servers may be bare metal or virtual and located on-premises or in the cloud.

Reusability

  • The same container image can be used to run identical containers in development, test, preproduction, and production environments.
  • There is no need to rebuild the image.

Rapidity

  • The container technology allows for accelerated application development, testing, deployment, patching, and scaling.
  • There is no need for an exhaustive testing.

Version Control

  • Container images can be version-controlled, which gives users the flexibility in choosing the right version to run a container.

Container Home: Bare Metal or Virtual Machine

Containers

  • run directly on the underlying operating system whether it be running on a bare metal server or in a virtual machine.
  • Share hardware and operating system resources securely among themselves.
  • Containerized applications stay lightweight and isolated, and run in parallel.
  • Share the same Linux kernel and require far fewer hardware resources than do virtual machines, which contributes to their speedy start and stop.
  • Given the presence of an extra layer of hypervisor services, it may be more beneficial and economical to run containers directly on non-virtualized physical servers.

Container Images and Container Registries

  • Launching a container requires a pre-packaged image to be available.

container image

  • Essentially a static file that is built with all necessary components (application binaries, library files, configuration settings, environment variables, static data files, etc.)

  • Required by an application to run smoothly, securely, and independently.

  • RHEL follows the open container initiative (OCI) to allow users to build images based on industry standard specifications that define the image format, host operating system metadata, and supported hardware architectures.

  • An OCI-compliant image can be executed and managed with OCI-compliant tools such as podman (pod manager) and Docker.

  • Images can be version-controlled giving users the suppleness to use the latest or any of the previous versions to launch their containers.

  • A single image can be used to run several containers at once.

  • Container images adhere to a standard naming convention for identification.

  • This is referred to as fully qualified image name (FQIN).

    • Comprised of four components:
      • (1) the storage location (registry_name)
      • (2) the owner or organization name (user_name)
      • (3) a unique repository name (repo_name)
      • (4) an optional version (tag).
    • The syntax of an FQIN is: registry_hostname/user_name/repo_name:tag.

  • Images are stored and maintained in public or private registries;

  • They need to be downloaded and made locally available for consumption.

  • There are several registries available on the Internet.

    • registry.redhat.io (/images/images based on official Red Hat products; requires authentication),
    • registry.access.redhat.com (requires no authentication)
    • registry.connect.redhat.com (/images/images based on third-party products)
    • hub.docker.com (Docker Hub).

  • The three Red Hat registries may be searched using the Red Hat Container Catalog at catalog.redhat.com/software/containers/search.

  • Additional registries may be added as required.

  • Private registries may also require authentication for access.

Rootful vs. Rootless Containers

  • Containers can be launched with the root user privileges (sudo or directly as the root user).

  • This gives containers full access to perform administrative functions including the ability to map privileged network ports (1024 and below).

  • Launching containers with superuser rights opens a gate to potential unauthorized access to the container host if a container is compromised due to a vulnerability or misconfiguration.

  • To secure containers and the underlying operating system, containers should be launched and interacted with as normal Linux users.

  • Such containers are referred to as rootless containers.

  • Rootless containers allow regular, unprivileged users to run containers without the ability to perform tasks that require privileged access.

Working with Images and Containers

Lab: Install Necessary Container Support

  • Install the necessary software to set the foundation for completing the exercises in the remainder of the chapter.
  • The standard RHEL 9.1 image includes a package called container-tools that consists of all the required components and commands.
  • Use the standard dnf command to install the package.

1. Install the container-tools package:

 root@server10 ~]# dnf install -y container-tools

 Upgraded:
  aardvark-dns-2:1.10.0-3.el9_4.x86_64 
  buildah-2:1.33.7-3.el9_4.x86_64         
  netavark-2:1.10.3-1.el9.x86_64            
  podman-4:4.9.4-6.el9_4.x86_64                                   
 Installed:
  container-tools-1-14.el9.noarch        
  podman-docker-4:4.9.4-6.el9_4.noarch 
  podman-remote-4:4.9.4-6.el9_4.x86_64    
  python3-podman-3:4.9.0-1.el9.noarch 
  python3-pyxdg-0.27-3.el9.noarch    
  python3-tomli-2.0.1-5.el9.noarch   
  skopeo-2:1.14.3-3.el9_4.x86_64             
  toolbox-0.0.99.5-2.el9.x86_64      
  udica-0.2.8-1.el9.noarch

2. Verify the package installation:

 [root@server10 ~]# dnf list container-tools
 Updating Subscription Management repositories.
 Last metadata expiration check: 14:53:32 ago on Wed 31 Jul 2024 05:45:56 PM MST.
 Installed Packages
 container-tools.noarch   1-14.el9    @rhel-9-for-x86_64-appstream-rpms

podman Command

  • Finding, inspect, retrieve, and delete images
  • Run, stop, list, and delete containers.
  • Used for most of these operations.

Subcommands

Image Management

build

  • Builds an image using instructions delineated in a Container file

images

  • Lists downloaded images from local storage

inspect

  • Examines an image and displays its details

login/logout

  • Logs in/out to/from a container registry. A login may be required to access private and protected registries.

pull

  • Downloads an image to local storage from a registry

rmi

  • Removes an image from local storage

search

  • Searches for an image. The following options can be included with this subcommand:
  1. A partial image name in the search will produce a list of all images containing the partial name.
  2. The --no-trunc option makes the command exhibit output without truncating it.
  3. The --limit <number> option limits the displayed results to the specified number.

tag

  • Adds a name to an image. The default is ’latest’ to classify the image as the latest version. Older images may have specific version identifiers.

Container Management

attach

  • Attaches to a running container

exec

  • Runs a process in a running container

generate

  • Generates a systemd unit configuration file that can be used to control the operational state of a container. The --new option is important and is employed in later exercises.

info

  • Reveals system information, including the defined registries

inspect

  • Exhibits the configuration of a container

ps

  • Lists running containers (includes stopped containers with the -a option)

rm

  • Removes a container

run

  • Launches a new container from an image. Some options such as -d (detached), -i (interactive), and -t (terminal) are important and are employed in exercises where needed.

start/stop/restart

  • Starts, stops, or restarts a container

skopeo Command

  • Utilized for interacting with local and remote images and registries.
  • Has numerous subcommands available; however, you will be using only the inspect subcommand to examine the details of an image stored in a remote registry.

/etc/containers/registries.conf

  • System-wide configuration file for image registries.
  • Normal Linux users may store a customized copy of this file, if required, under the ~/.config/containers directory.
  • Settings stored in the per-user file will take precedence over those stored in the system-wide file.
    • Useful for running rootless containers.
  • Defines searchable and blocked registries.
 [root@server10 ~]# grep -Ev '^#|^$' /etc/containers/registries.conf
 unqualified-search-registries = ["registry.access.redhat.com", "registry.redhat.io", "docker.io"]
 short-name-mode = "enforcing"
  • The output shows three registries.
  • The podman command searches these registries for container images in the given order.
  • Can add additional registries to the list.

Add a private registry called registry.private.myorg.io to be added with the highest priority:

 [root@server10 ~]# vim /etc/containers/registries.conf
 unqualified-search-registries = \["registry.private.myorg.io",
 "registry.access.redhat.com", "registry.redhat.io", "docker.io"\]

If this private registry is the only one to be used, you can take the rest of the registry entries out of the list:

 unqualified-search-registries = \["registry.private.myorg.io"\]

EXAM TIP: As there is no Internet access provided during Red Hat exams, you may have to access a network-based registry to download images.

Viewing Podman Configuration and Version

  • The podman command references various system runtime and configuration files and runs certain Linux commands in the background to gather and display information.
  • For instance, it looks for registries and storage data in the system-wide and per-user configuration files, pulls memory information from the /proc/meminfo file, executes uname -rto obtain the kernel version, and so on.
  • podman’s info subcommand shows all this information.

Here is a sample when this command is executed as a normal user (user1):

 [[user1@server10 root]$ podman info
 ERRO[0000] XDG_RUNTIME_DIR directory "/run/user/0" is not owned by the current user](<[user1@server10 ~]$ podman info
 host:
  arch: amd64
  buildahVersion: 1.33.8
  cgroupControllers:
  - memory
  - pids
  cgroupManager: systemd
  cgroupVersion: v2
  conmon:
 ...

  • Re-run the command as root (preceded by sudo if running as user1) and compare the values for the settings “rootless” under host and “ConfigFile” and “ImageStore” under store.

  • The differences lie between where the root and rootless (normal) users store and obtain configuration data, the number of container images they have locally available, and so on.

 [root@server10 ~]# podman info
 host:
  arch: amd64
  buildahVersion: 1.33.8
  cgroupControllers:
  - cpuset
  - cpu
  - io
  - memory
  - hugetlb
  - pids
  - rdma
  - misc
...

Similarly, you can run the podman command as follows to check its version:

 [root@server10 ~]# podman version
 Client:       Podman Engine
 Version:      4.9.4-rhel
 API Version:  4.9.4-rhel
 Go Version:   go1.21.11 (Red Hat 1.21.11-1.el9_4)
 Built:        Mon Jul  1 03:27:14 2024
 OS/Arch:      linux/amd64

Image Management

Container images

  • Are available from numerous private and public registries.
  • They are pre-built for a variety of use cases.
  • You can search through registries to find the one that suits your needs.
  • You can examine their metadata before downloading them for consumption.
  • Downloaded images can be removed when no longer needed to conserve local storage.
  • The same pair of commands—podman and skopeo—is employed for these operations.

Lab: Search, Examine, Download, and Remove an Image

  • Log in to the registry.access.redhat.com registry
  • Look for an image called mysql-80 in the registry, examine its details, pull it to your system, confirm the retrieval, and finally erase it from the local storage.

1. Log in to the specified Red Hat registry:

 [user1@server10 ~]$ podman login registry.redhat.io

2. Confirm a successful login:

 [user1@server10 ~]$ podman login registry.redhat.io --get-login

3. Find the mysql-80 image in the specified registry. Add the --no-trunc option to view full output.

 [user1@server10 ~]$ podman search registry.redhat.io/mysql-80 --no-trunc
 NAME                                     DESCRIPTION
 registry.redhat.io/rhel8/mysql-80        This container image provides a containerized packaging of the MySQL mysqld daemon and client application. The  mysqld server daemon accepts connections from clients and provides access to content from MySQL databases on behalf of the clients.
...

4. Select the second image rhel9/mysql-80 for this exercise. Inspect the image without downloading it using skopeo inspect. A long output will be generated. The command uses the docker:// mechanism to access the image.

 [user1@server10 ~]$ skopeo inspect docker://registry.redhat.io/rhel9/mysql-80
 {
    "Name": "registry.redhat.io/rhel9/mysql-80",
    "Digest": "sha256:247903d2103a3c1db9401f6340ecdcd97c6244480b7a3419e6303dda650491dc",
    "RepoTags": [
        "1",
        "1-190",
        "1-190.1655192188",
        "1-190.1655192188-source",
        "1-190-source",
        "1-197",
        "1-197-source",
        "1-206",
...

Output:

  • Shows older versions under RepoTags

  • Creation time for the latest version

  • Build date of the image

  • description

  • other information.

  • It is a good practice to analyze the metadata of an image prior to downloading and consuming it.

5. Download the image by specifying the fully qualified image name using podman pull:

 [user1@server10 ~]$ podman pull docker://registry.redhat.io/rhel9/mysql-80
 Trying to pull registry.redhat.io/rhel9/mysql-80:latest...
 Getting image source signatures
 Checking if image destination supports signatures
 Copying blob 846c0bdf4e30 done   | 
 Copying blob cc296d75b612 done   | 
 Copying blob db22e630b1c7 done   | 
 Copying config b5782120a3 done   | 
 Writing manifest to image destination
 Storing signatures
 b5782120a320e5915d86555e661c357cfa56dd8320ba4c54a58caa1e1c91925f

6. List the image to confirm the retrieval using podman images:

 [user1@server10 ~]$ podman images
 REPOSITORY                         TAG         IMAGE ID      CREATED      SIZE
 registry.redhat.io/rhel9/mysql-80  latest      b5782120a320  2 weeks ago  555 MB

7. Display the image’s details using podman inspect:

 [user1@server10 ~]$ podman inspect mysql-80
 [
     {
          "Id": "b5782120a320e5915d86555e661c357cfa56dd8320ba4c54a58caa1e1c91925f",
          "Digest": "sha256:247903d2103a3c1db9401f6340ecdcd97c6244480b7a3419e6303dda650491dc",
          "RepoTags": [
               "registry.redhat.io/rhel9/mysql-80:latest"
          ],

8. Remove the mysql-80 image from local storage:

 [user1@server10 ~]$ podman rmi mysql-80
 Untagged: registry.redhat.io/rhel9/mysql-80:latest
 Deleted: b5782120a320e5915d86555e661c357cfa56dd8320ba4c54a58caa1e1c91925f
  • Shows the ID of the image after deletion.

9. Confirm the removal:

 [user1@server10 ~]$ podman images
 REPOSITORY  TAG         IMAGE ID    CREATED     SIZE

Containerfile

  • Can build a custom image by outlining the steps you need to be run in a file called Containerfile.
  • The podman command can then be used to read those instructions and executes them to produce a new image.
  • File name containerfile is widespread; but you can use any name of your liking.

Instructions that may be utilized inside a Containerfile to perform specific functions during the build process:

CMD

  • Runs a command

COPY

  • Copies files to the specified location

ENV

  • Defines environment variables to be used during the build process

EXPOSE

  • A port number that will be opened when a container is launched using this image

FROM

  • Identifies the base container image to use

RUN

  • Executes the specified commands

USER

  • Defines a non-root user to run the commands as

WORKDIR

  • Sets the working directory. This directory is automatically created if it does not already exist.

A sample container file is presented below:

 [user1@server10 ~]$ vim containerfile
 # Use RHEL9 base image
 FROM registry.redhat.io/ubi9/ubi

 # Install Apache web server software
 RUN dnf -y install httpd

 # Copy the website
 COPY ./index.html /var/www/html/

 # Expose Port 80/tcp
 EXPOSE 80

 # Start Apache web server
 CMD ["httpd"]
  • The index.html file may contain a basic statement such as “This is a custom-built Apache web server container image based on RHEL 9”.

Lab: Use Containerfile to Build Image

  • Use a containerfile to build a custom image based on the latest version of the RHEL 9 universal base image (ubi) available from a Red Hat container registry.
  • Confirm the image creation.
  • Use the podman command for these activities.

1. Log in to the specified Red Hat registry:

 [user1@server10 ~]$ podman login registry.redhat.io
 Authenticating with existing credentials for registry.redhat.io
 Existing credentials are valid. Already logged in to registry.redhat.io

2. Confirm a successful login:

 [user1@server10 ~]$ podman login registry.redhat.io --get-login

3. Create a file called containerfile with the following code:

 [user1@server10 ~]$ vim containerfile2
 # Use RHEL9 base image
 FROM registry.redhat.io/ubi9/ubi

 # Count the number of characters
 CMD echo "RHCSA exam is hands-on." | wc

 # Copy a local file to /tmp
 COPY ./testfile /tmp

4. Create a file called testfile with some random text in it and place it in the same directory as the containerfile.

 [user1@server10 ~]$ echo "boo bee doo bee doo" >> testfile
 [user1@server10 ~]$ cat testfile 
 boo bee doo bee doo

5. Build an image by specifying the containerfile name and an image tag such as ubi9-simple-image. The period character at the end represents the current directory and this is where both containerfile and testfile are located.

 [user1@server10 ~]$ podman image build -f containerfile2 -t ubi9-simple-image .
 STEP 1/3: FROM registry.redhat.io/ubi9/ubi
 Trying to pull registry.redhat.io/ubi9/ubi:latest...
 Getting image source signatures
 Checking if image destination supports signatures
 Copying blob cc296d75b612 done   | 
 Copying config 159a1e6731 done   | 
 Writing manifest to image destination
 Storing signatures
 STEP 2/3: CMD echo "RHCSA exam is hands-on." | wc
 --> 4c005bfd0b34
 STEP 3/3: COPY ./testfile /tmp
 COMMIT ubi9-simple-image
 --> a2797b06a129
 Successfully tagged localhost/ubi9-simple-image:latest
 a2797b06a1294ed06edab2ba1c21d2bddde3eb3af1d8ed286781837f62992622

6. Confirm image creation:

 [user1@server10 ~]$ podman image ls
 REPOSITORY                   TAG         IMAGE ID      CREATED        SIZE
 localhost/ubi9-simple-image  latest      a2797b06a129  2 minutes ago  220 MB
 registry.redhat.io/ubi9/ubi  latest      159a1e67312e  2 weeks ago    220 MB

Output:

  • downloaded image

  • new custom image along with their image IDs, creation time, and size.

  • Do not remove the custom image yet as you will be using it to launch a container in the next section.

Basic Container Management

  • Starting, stopping, listing, viewing information about, and deleting them.
  • Depending on the use case, containers can be launched in different ways.
  • They can:
    • Have a name assigned or be nameless
    • Have a terminal session opened for interaction
    • Execute an entry point command (the command specified at the launch time) and be auto-terminated right after.
    • etc.
  • Running containers can be stopped and restarted, or discarded if no longer needed.
  • The podman command is utilized to start containers and manage their lifecycle.
  • This command is also employed to list stopped and running containers, and view their details.

Lab: Run, Interact with, and Remove a Named Container

  • Run a container based on the latest version of the RHEL 8 ubi available in the Red Hat container registry.
  • Assign this container a name and run a few native Linux commands in a terminal window interactively.
  • Exit out of the container to mark the completion of the exercise.

1. Launch a container using ubi8 (RHEL 8). Name this container rhel8-base-os and open a terminal session for interaction:

 [user1@server10 ~]$ podman run -ti --name rhel8-base-os ubi8
 Resolved "ubi8" as an alias (/etc/containers/registries.conf.d/001-rhel-shortnames.conf)
 Trying to pull registry.access.redhat.com/ubi8:latest...
 Getting image source signatures
 Checking if image destination supports signatures
 Copying blob 8694db102e5b done   | 
 Copying config 269749ad51 done   | 
 Writing manifest to image destination
 Storing signatures
 [root@30c7cccd8490 /]#

  • Downloaded the latest version of the specified image automatically even though no FQIN was provided.

    • This is because it searched through the registries listed in the /etc/containers/registries.conf file and retrieved the image from wherever it found it first (registry.access.redhat.com).

  • Opened a terminal session inside the container as the root user to interact with the containerized RHEL 8 OS.

  • The container ID is reflected as the hostname in the container’s command prompt (last line in the output). This is an auto-generated ID.

  • If you encounter any permission issues, delete the /etc/docker directory (if it exists) and try again.

2. Run a few basic commands such as pwd, ls, cat, and date inside the container for verification:

 [root@30c7cccd8490 /]# pwd
 /
 [root@30c7cccd8490 /]# ls
 bin   dev  home  lib64	     media  opt   root	sbin  sys  usr
 boot  etc  lib	 lost+found  mnt    proc  run	srv   tmp  var
 [root@30c7cccd8490 /]# cat /etc/redhat-release
 Red Hat Enterprise Linux release 8.10 (Ootpa)
 [root@30c7cccd8490 /]# date
 Thu Aug  1 21:09:13 UTC 2024

3. Close the terminal session when done:

 [root@30c7cccd8490 /]# exit
 exit
 [user1@server10 ~]$

4. Delete the container using podman rm:

 [user1@server10 ~]$ podman rm rhel8-base-os
 rhel8-base-os

Confirm the removal with podman ps.

 [user1@server10 ~]$ podman ps
 CONTAINER ID  IMAGE       COMMAND     CREATED     STATUS      PORTS       NAMES

Lab: Run a Nameless Container and Auto-Remove it After Entry Point Command Execution

  • Launch a container based on the latest version of RHEL 7 ubi available in a Red Hat container registry.
    • This image provides the base operating system layer to deploy containerized applications.
  • Enter a Linux command at the command line for execution inside the container as an entry point command and the container should be automatically deleted right after that.

1. Start a container using ubi7 (RHEL 7) and run ls as an entry point command. Remove the container as soon as the entry point command has finished running.

 [user1@server10 ~]$ podman run --rm ubi7 ls
 Resolved "ubi7" as an alias (/etc/containers/registries.conf.d/001-rhel-shortnames.conf)
 Trying to pull registry.access.redhat.com/ubi7:latest...
 Getting image source signatures
 Checking if image destination supports signatures
 Copying blob 7f2c2c4492b6 done   | 
 Copying config a084eb42a5 done   | 
 Writing manifest to image destination
 Storing signatures
 bin
 boot
 dev
 etc
 home
...

2. Confirm the container removal with podman ps:

podman ps
 CONTAINER ID  IMAGE       COMMAND     CREATED     STATUS      PORTS       NAMES

Advanced Container Management

  • Preset environment variables may be passed when launching containers or new variables may be set for containerized applications to consume for proper operation.
  • Information stored during an application execution is lost when a container is restarted or erased.
  • This behavior can be overridden by making a directory on the host available inside the container for saving data persistently.
  • Containers may be configured to start and stop with the transitioning of the host system via the systemd service. These advanced tasks are also performed with the podman command.

Containers and Port Mapping

  • Applications running in different containers often need to exchange data for proper operation.
  • For instance, a containerized Apache web server may need to talk to a MySQL database instance running in a different container.
  • It may also need to talk to the outside world over a port such as 80 or 8080.
  • To support this traffic flow, appropriate port mappings are established between the host system and each container.

EXAM TIP: As a normal user, you cannot map a host port below 1024 to a container port.

Lab: Configure Port Mapping

  • Launch a container called rhel7-port-map in detached mode (as a daemon) with host port 10000 mapped to port 8000 inside the container.
  • Use a version of the RHEL 7 image with Apache web server software pre-installed.
  • This image is available from a Red Hat container registry.
  • List the running container and confirm the port mapping.

1. Search for an Apache web server image for RHEL 7 using podman search:

 [user1@server30 ~]$ podman search registry.redhat.io/rhel7/httpd
 NAME                                      DESCRIPTION
 registry.redhat.io/rhscl/httpd-24-rhel7   Apache HTTP 2.4 Server

2. Log in to registry.redhat.io using the Red Hat credentials to access the image:

 [user1@server30 ~]$ podman login registry.redhat.io
 Username: tdavetech@gmail.com
 Password: 
 Login Succeeded!

3. Download the latest version of the Apache image using podman pull:

 [user1@server30 ~]$ podman pull registry.redhat.io/rhscl/httpd-24- rhel7
 Trying to pull registry.redhat.io/rhscl/httpd-24-rhel7:latest...
 Getting image source signatures
 Checking if image destination supports signatures
 Copying blob fd77da0b900b done   | 
 Copying blob 7f2c2c4492b6 done   | 
 Copying blob ea092d7970b2 done   | 
 Copying config 847db19d6c done   | 
 Writing manifest to image destination
 Storing signatures
 847db19d6cbc726106c901a7713d30dccc9033031ec812037c4c458319a1b328

4. Verify the download using podman images:

 [user1@server30 ~]$ podman images
 REPOSITORY                               TAG         IMAGE ID       CREATED       SIZE
 registry.redhat.io/rhscl/httpd-24-rhel7  latest      847db19d6cbc  2  months ago  332 MB

5. Launch a container named rhel7-port-map in detached mode to run the containerized Apache web server with host port 10000 mapped to container port 8000.

 [user1@server30 ~]$ podman run -dp 10000:8000 --name rhel7-port-map  httpd-24-rhel7
 cd063dff352dfbcd57dd417587513b12ca4033ed657f3baaa28d54df19d4df1c

6. Verify that the container was launched successfully using podman ps:

 [user1@server30 ~]$ podman ps
 CONTAINER ID  IMAGE                                           COMMAND               CREATED         STATUS         PORTS                    NAMES
 cd063dff352d  registry.redhat.io/rhscl/httpd-24-rhel7:latest   /usr/bin/run-http...  36 seconds ago  Up 36 seconds  0.0.0.0:10000- >8000/tcp  rhel7-port-map

7. You can also use podman port to view the mapping:

 [user1@server30 ~]$ podman port rhel7-port-map
 8000/tcp -> 0.0.0.0:10000
  • Now any inbound web traffic on host port 10000 will be redirected to the container.

Exercise 22-7: Stop, Restart, and Remove a Container

  • Stop the container, restart it, stop it again, and then erase it.
  • Use appropriate podman subcommands and verify each transition.

1. Verify the current operational state of the container rhel7-port-map:

 [user1@server30 ~]$ podman ps
 CONTAINER ID  IMAGE                                           COMMAND               CREATED        STATUS        PORTS                    NAMES
 cd063dff352d  registry.redhat.io/rhscl/httpd-24-rhel7:latest   /usr/bin/run-http...  3 minutes ago  Up 3 minutes  0.0.0.0:10000- >8000/tcp  rhel7-port-map

2. Stop the container and confirm. (the -a option with ps also includes the stopped containers in the output):

 [user1@server30 ~]$ podman stop rhel7-port-map
 rhel7-port-map

 [user1@server30 ~]$ podman ps -a
 CONTAINER ID  IMAGE                                           COMMAND               CREATED        STATUS                    PORTS                    NAMES
 cd063dff352d  registry.redhat.io/rhscl/httpd-24-rhel7:latest   /usr/bin/run-http...  6 minutes ago  Exited (0) 5 seconds ago   0.0.0.0:10000->8000/tcp  rhel7-port-map

3. Start the container and confirm:

 [user1@server30 ~]$ podman start rhel7-port-map
 rhel7-port-map
 [user1@server30 ~]$ podman ps -a
 CONTAINER ID  IMAGE                                           COMMAND               CREATED        STATUS         PORTS                    NAMES
 cd063dff352d  registry.redhat.io/rhscl/httpd-24-rhel7:latest   /usr/bin/run-http...  8 minutes ago  Up 11 seconds  0.0.0.0:10000- >8000/tcp  rhel7-port-map

4. Stop the container and remove it:

 [user1@server30 ~]$ podman rm rhel7-port-map
 rhel7-port-map

5. Confirm the removal:

 [user1@server30 ~]$ podman ps -a
 CONTAINER ID  IMAGE       COMMAND     CREATED     STATUS      PORTS       NAMES

Containers and Environment Variables

  • Many times it is necessary to pass a host’s pre-defined environment variable, such as PATH, to a containerized application for consumption.
  • Moreover, it may also be necessary at times to set new variables to inject debugging flags or sensitive information such as passwords, access keys, or other secrets for use inside containers.
  • Passing host environment variables or setting new environment variables is done at the time of launching a container.
  • The podman command allows multiple variables to be passed or set with the -e option.

EXAM TIP: Use the -e option with each variable that you want to pass or set.

Lab: Pass and Set Environment Variables

  • Launch a container using the latest version of a ubi for RHEL 9 available in a Red Hat container registry.
  • Inject the HISTSIZE environment variable, and a variable called SECRET with a value “secret123”.
  • Name this container rhel9-env-vars and have a shell terminal opened to check the variable settings.
  • Remove this container.

1. Launch a container with an interactive terminal session and inject variables HISTSIZE and SECRET as directed. Use the specified container image.

 [user1@server30 ~]$ podman run -it -e HISTSIZE -e SECRET="secret123" --name rhel9-env-vars ubi9
 Resolved "ubi9" as an alias (/etc/containers/registries.conf.d/001- rhel-shortnames.conf)
 Trying to pull registry.access.redhat.com/ubi9:latest...
 Getting image source signatures
 Checking if image destination supports signatures
 Copying blob cc296d75b612 done   | 
 Copying config 159a1e6731 done   | 
 Writing manifest to image destination
 Storing signatures
 [root@b587355b8fc1 /]#

2. Verify both variables using the echo command:

 [root@b587355b8fc1 /]# echo $HISTSIZE $SECRET
 1000 secret123
 [root@b587355b8fc1 /]#

3. Disconnect from the container, and stop and remove it:

 [user1@server30 ~]$ podman stop rhel9-env-vars
 rhel9-env-vars
 [user1@server30 ~]$ podman rm rhel9-env-vars
 rhel9-env-vars

Confirm the deletion:

 [user1@server30 ~]$ podman ps -a
 CONTAINER ID  IMAGE       COMMAND     CREATED     STATUS      PORTS       NAMES

Containers and Persistent Storage

  • Containers are normally launched for a period of time to run an application and then stopped or deleted when their job is finished.
  • Any data that is produced during runtime is lost on their restart, failure, or termination.
  • This data may be saved for persistence on a host directory by attaching the host directory to a container.
  • The containerized application will see the attached directory just like any other local directory and will use it to store data if it is configured to do so.
  • Any data that is saved on the directory will be available even after the container is rebooted or removed.
  • Later, this directory can be re-attached to other containers to give them access to the stored data or to save their own data.
  • The source directory on the host may itself exist on any local or remote file system.

EXAM TIP: Proper ownership, permissions, and SELinux file type must be set to ensure persistent storage is accessed and allows data writes without issues.

  • There are a few simple steps that should be performed to configure a host directory before it can be attached to a container.
  • These steps include the correct ownership, permissions, and SELinux type (container_file_t).
  • The special SELinux file type is applied to prevent containerized applications (especially those running in root containers) from gaining undesired privileged access to host files and processes, or other running containers on the host if compromised.

Lab: Attach Persistent Storage and Access Data Across Containers

  • Set up a directory on server20 and attach it to a new container.
  • Write some data to the directory while in the container.
  • Delete the container and launch another container with the same directory attached.
  • Observe the persistence of saved data in the new container and that it is accessible.
  • Remove the container to mark the completion of this exercise.

1. Create a directory called /host_data, set full permissions on it, and confirm:

 [user1@server30 ~]$ sudo mkdir /host_data
 [sudo] password for user1: 
 [user1@server30 ~]$ sudo chmod 777 /host_data/
 [user1@server30 ~]$ ll -d /host_data/
 drwxrwxrwx. 2 root root 6 Aug  1 22:59 /host_data/

2. Launch a root container called rhel9-persistent-data in interactive mode using the latest ubi9 image. Specify the attachment point (/container_data) to be used inside the container for the host directory (/host_data) Ensure the SELinux type container_file_t is automatically set on the directory and files within.

 [user1@server30 ~]$ sudo podman run --name rhel9-persistent-data -v  /host_data:/container_data:Z -it ubi9
 Resolved "ubi9" as an alias (/etc/containers/registries.conf.d/001- rhel-shortnames.conf)
 Trying to pull registry.access.redhat.com/ubi9:latest...
 Getting image source signatures
 Checking if image destination supports signatures
 Copying blob cc296d75b612 done   | 
 Copying config 159a1e6731 done   | 
 Writing manifest to image destination
 Storing signatures

3. Confirm the presence of the directory inside the container with ls on /container_data:

 [root@e8711892370f /]# ls -ldZ /container_data
 drwxrwxrwx. 2 root root  system_u:object_r:container_file_t:s0:c376,c965 6 Aug  2 05:59  /container_data

4. Create a file called testfile with the echo command under /container_data:

 [root@e8711892370f /]# echo "This is persistent storage." >  /container_data/testfile

5. Verify the file creation and the SELinux type on it:

 [root@e8711892370f /]# ls -lZ /container_data/
 total 4
 -rw-r--r--. 1 root root  system_u:object_r:container_file_t:s0:c376,c965 28 Aug  2 06:03  testfile

6. Exit out of the container and check the presence of the file in the host directory:

 [root@e8711892370f /]# exit
 exit
 [user1@server30 ~]$ ls -lZ /host_data/
 total 4
 -rw-r--r--. 1 root root  system_u:object_r:container_file_t:s0:c376,c965 28 Aug  1 23:03  testfile

7. Stop and remove the container:

 [user1@server30 ~]$ sudo podman stop rhel9-persistent-data
 rhel9-persistent-data
 [user1@server30 ~]$ sudo podman rm rhel9-persistent-data
 rhel9-persistent-data

8. Launch a new root container called rhel8-persistent-data in interactive mode using the latest ubi8 image from any of the defined registries. Specify the attachment point (/container_data2) to be used inside the container for the host directory (/host_data). Ensure the SELinux type container_file_t is automatically set on the directory and files within.

 [user1@server30 ~]$ sudo podman run -it --name rhel8-persistent-data -v /host_data:/container_data2:Z ubi8
 Resolved "ubi8" as an alias (/etc/containers/registries.conf.d/001- rhel-shortnames.conf)
 Trying to pull registry.access.redhat.com/ubi8:latest...
 Getting image source signatures
 Checking if image destination supports signatures
 Copying blob 8694db102e5b done   | 
 Copying config 269749ad51 done   | 
 Writing manifest to image destination
 Storing signatures

9. Confirm the presence of the directory inside the container with ls on /container_data2:

 [root@af6773299c7e /]# ls -ldZ /container_data2/
 drwxrwxrwx. 2 root root  system_u:object_r:container_file_t:s0:c198,c914 22 Aug  2 06:03  /container_data2/
 [root@af6773299c7e /]# ls -lZ /container_data2/
 total 4
 -rw-r--r--. 1 root root  system_u:object_r:container_file_t:s0:c198,c914 28 Aug  2 06:03  testfile
 [root@af6773299c7e /]# cat /container_data2/testfile
 This is persistent storage.

10. Create a file called testfile2 with the echo command under /container_data2:

 [root@af6773299c7e /]# echo "This is persistent storage2." >  /container_data2/testfile2

 [root@af6773299c7e /]# ls -lZ /container_data2/
 total 8
 -rw-r--r--. 1 root root  system_u:object_r:container_file_t:s0:c198,c914 28 Aug  2 06:03  testfile
 -rw-r--r--. 1 root root  system_u:object_r:container_file_t:s0:c198,c914 29 Aug  2 06:10  testfile2

11. Exit out of the container and confirm the existence of both files in the host directory:

 [root@af6773299c7e /]# exit
 exit

 [user1@server30 ~]$ ls -lZ /host_data/
 total 8
 -rw-r--r--. 1 root root  system_u:object_r:container_file_t:s0:c198,c914 28 Aug  1 23:03  testfile
 -rw-r--r--. 1 root root  system_u:object_r:container_file_t:s0:c198,c914 29 Aug  1 23:10  testfile2

12. Stop and remove the container using the stop and rm subcommands:

 [user1@server30 ~]$ sudo podman stop rhel8-persistent-data
 rhel8-persistent-data
 [user1@server30 ~]$ sudo podman rm rhel8-persistent-data
 rhel8-persistent-data

13. Re-check the presence of the files in the host directory:

 [user1@server30 ~]$ ll /host_data
 total 8
 -rw-r--r--. 1 root root 28 Aug  1 23:03 testfile
 -rw-r--r--. 1 root root 29 Aug  1 23:10 testfile2

Container State Management with systemd

  • Multiple containers run on a single host and it becomes a challenging task to change their operational state or delete them manually.

  • In RHEL 9, these administrative functions can be automated via the systemd service

  • There are several steps that need to be completed to configure container state management via systemd.

  • These steps vary for rootful and rootless container setups and include the creation of service unit files and their storage in appropriate directory locations (~/.config/systemd/user for rootless containers and /etc/systemd/system for rootful containers).

  • Once setup and enabled, the containers will start and stop automatically as a systemd service with the host state transition or manually with the systemctl command.

  • The podman command to start and stop containers is no longer needed if the systemd setup is in place.

  • You may experience issues if you continue to use podman for container state transitioning alongside.

  • The start and stop behavior for rootless containers differs slightly from that of rootful containers.

  • For the rootless setup, the containers are started when the relevant user logs in to the host and stopped when that user logs off from all their open terminal sessions;

  • However, this default behavior can be altered by enabling lingering for that user with the loginctl command.

  • User lingering is a feature that, if enabled for a particular user, spawns a user manager for that user at system startup and keeps it running in the background to support long-running services configured for that user.

  • The user need not log in.

EXAM TIP: Make sure that you use a normal user to launch rootless containers and the root user (or sudo) for rootful containers.

  • Rootless setup does not require elevated privileges of the root user.

Lab: Configure a Rootful Container as a systemd Service

  • Create a systemd unit configuration file for managing the state of your rootful containers.
  • Launch a new container and use it as a template to generate a service unit file.
  • Stop and remove the launched container to avoid conflicts with new containers that will start.
  • Use the systemctl command to verify the automatic container start, stop, and deletion.

1. Launch a new container called rootful-container in detached mode using the latest ubi9:

 [user1@server30 ~]$ sudo podman run -dt --name rootful-container ubi9
 [sudo] password for user1: 
 0ed04dcedec418068acd14c864e95e78f56a38dd57d2349cf2c46b0de1a1bf1b

2. Confirm the new container using podman ps. Note the container ID.

 [user1@server30 ~]$ sudo podman ps
 CONTAINER ID  IMAGE                                   COMMAND      CREATED         STATUS         PORTS       NAMES
 0ed04dcedec4  registry.access.redhat.com/ubi9:latest  /bin/bash   20  seconds ago  Up 20 seconds              rootful-container

3. Create (generate) a service unit file called rootful-container.service under /etc/systemd/system while ensuring that the next new container that will be launched based on this configuration file will not require the source container to work. The tee command will show the generated file content on the screen as well as store it in the specified file.

 [user1@server30 ~]$ sudo podman generate systemd --new --name  rootful-container | sudo tee /etc/systemd/system/rootful-qcontainer.service

 [Unit]
 Description=Podman container-rootful-container.service
 Documentation=man:podman-generate-systemd(1)
 Wants=network-online.target
 After=network-online.target
 RequiresMountsFor=%t/containers

 [Service]
 Environment=PODMAN_SYSTEMD_UNIT=%n
 Restart=on-failure
 TimeoutStopSec=70
 ExecStart=/usr/bin/podman run \
	--cidfile=%t/%n.ctr-id \
	--cgroups=no-conmon \
	--rm \
	--sdnotify=conmon \
	--replace \
	-dt \
	--name rootful-container ubi9
 ExecStop=/usr/bin/podman stop \
	--ignore -t 10 \
	--cidfile=%t/%n.ctr-id
 ExecStopPost=/usr/bin/podman rm \
	-f \
	--ignore -t 10 \
	--cidfile=%t/%n.ctr-id
 Type=notify
 NotifyAccess=all

 [Install]
 WantedBy=default.target
  • The unit file has the same syntax as any other systemd service configuration file.
  • There are three sections—Unit, Service, and Install.
    • (1) The unit section provides a short description of the service, the manual page location, and the dependencies (wants and after).
    • (2) The service section highlights the full commands for starting (ExecStart) and stopping (ExecStop) containers.
      • It also highlights the commands that will be executed before the container start (ExecStartPre) and after the container stop (ExecStopPost).
      • There are a number of options and arguments with the commands to ensure a proper transition.
      • The restart on-failure stipulates that systemd will try to restart the container in the event of a failure.
    • (3) The install section identifies the operational target the host needs to be running in before this container service can start.

4. Stop and delete the source container (rootful-container):

 [user1@server30 ~]$ sudo podman stop rootful-container
 [sudo] password for user1: 
 WARN[0010] StopSignal SIGTERM failed to stop container rootful- container in 10 seconds, resorting to SIGKILL 
 rootful-container

 [user1@server30 ~]$ sudo podman rm rootful-container
 rootful-container

Verify the removal by running sudo podman ps -a:

 [user1@server30 ~]$ sudo podman ps -a
 CONTAINER ID  IMAGE       COMMAND     CREATED     STATUS      PORTS       NAMES

5. Update systemd to bring the new service under its control (reboot the system if required):

 [user1@server30 ~]$ sudo systemctl daemon-reload

6. Enable and start the container service:

 [user1@server30 ~]$ sudo systemctl enable --now rootful-container
 Created symlink /etc/systemd/system/default.target.wants/rootful- container.service → /etc/systemd/system/rootful-container.service.

7. Check the running status of the new service:

 [user1@server30 ~]$ sudo systemctl status rootful-container
 rootful-container.service - Podman container-rootful-container.s>
     Loaded: loaded (/etc/systemd/system/rootful-container.service>
     Active: active (running)

8. Verify the launch of a new container (compare the container ID with that of the source root container):

 [user1@server30 ~]$ sudo podman ps
 CONTAINER ID  IMAGE                                   COMMAND      CREATED             STATUS             PORTS       NAMES
 440a57c26186  registry.access.redhat.com/ubi9:latest  /bin/bash    About a minute ago  Up About a minute              rootful-container

9. Restart the container service using the systemctl command:

 [user1@server30 ~]$ sudo systemctl restart rootful-container
 sudo systemctl status rootful-

 [user1@server30 ~]$ sudo systemctl status rootful-container
 rootful-container.service - Podman container-rootful-container.s>
     Loaded: loaded (/etc/systemd/system/rootful-container.service>
     Active: active (running)

10. Check the status of the container again. Observe the removal of the previous container and the launch of a new container (compare container IDs).

 [user1@server30 ~]$ sudo podman ps
 CONTAINER ID  IMAGE                                   COMMAND      CREATED         STATUS             PORTS       NAMES
 0a980537b83a  registry.access.redhat.com/ubi9:latest  /bin/bash   59  seconds ago  Up About a minute              rootful-container
  • Each time the rootful-container service is restarted or server20 is rebooted, a new container will be launched.

Lab: Configure Rootless Container as a systemd Service

  • Create a systemd unit configuration file for managing the state of your rootless containers.
  • Launch a new container as conuser1 (create this user) and use it as a template to generate a service unit file.
  • Stop and remove the launched container to avoid conflicts with new containers that will start.
  • Use the systemctl command as conuser1 to verify the automatic container start, stop, and deletion.

1. Create a user account called conuser1 and assign a simple password:

 [user1@server30 ~]$ sudo useradd conuser1

 [user1@server30 ~]$ echo conuser1 | sudo passwd -- stdin conuser1
 Changing password for user conuser1.
 passwd: all authentication tokens updated  successfully.

2. Open a new terminal window on server20 and log in as conuser1. Create directory ~/.config/systemd/user to store a service unit file:

 [conuser1@server30 ~]$ mkdir ~/.config/systemd/user -p

3. Launch a new container called rootless-container in detached mode using the latest ubi8:

 [conuser1@server30 ~]$ podman run -dt --name  rootless-container ubi8
 Resolved "ubi8" as an alias  (/etc/containers/registries.conf.d/001-rhel- shortnames.conf)
 Trying to pull  registry.access.redhat.com/ubi8:latest...
 Getting image source signatures
 Checking if image destination supports signatures
 Copying blob 8694db102e5b done   | 
 Copying config 269749ad51 done   | 
 Writing manifest to image destination
 Storing signatures
 381d46ae9a3e11723c3bde35090782129e6937c461f8c2621bc9725f6b9efc27

4. Confirm the new container using podman ps. Note the container ID.

 [conuser1@server30 ~]$ podman ps
 CONTAINER ID  IMAGE                                   COMMAND     CREATED         STATUS         PORTS       NAMES
 381d46ae9a3e  registry.access.redhat.com/ubi8:latest  /bin/bash   27 seconds ago  Up 27 seconds              rootless-container

5. Create (generate) a service unit file called rootless-container.service under ~/.config/systemd/user while ensuring that the next new container that will be launched based on this configuration will not require the source container to work:

 [conuser1@server30 ~]$ podman generate systemd --new --name rootless-container >  ~/.config/systemd/user/rootless-container.service

 DEPRECATED command:
 It is recommended to use Quadlets for running  containers and pods under systemd.

 Please refer to podman-systemd.unit(5) for details.

6. Display the content of the unit file:

 [conuser1@server30 ~]$ cat  ~/.config/systemd/user/rootless-container.service 
 # container-rootless-container.service
 # autogenerated by Podman 4.9.4-rhel
 # Thu Aug  1 23:42:11 MST 2024

 [Unit]
 Description=Podman container-rootless- container.service
 Documentation=man:podman-generate-systemd(1)
 Wants=network-online.target
 After=network-online.target
 RequiresMountsFor=%t/containers

 [Service]
 Environment=PODMAN_SYSTEMD_UNIT=%n
 Restart=on-failure
 TimeoutStopSec=70
 ExecStart=/usr/bin/podman run \
	--cidfile=%t/%n.ctr-id \
	--cgroups=no-conmon \
	--rm \
	--sdnotify=conmon \
	--replace \
	-dt \
	--name rootless-container ubi8
 ExecStop=/usr/bin/podman stop \
	--ignore -t 10 \
	--cidfile=%t/%n.ctr-id
 ExecStopPost=/usr/bin/podman rm \
	-f \
	--ignore -t 10 \
	--cidfile=%t/%n.ctr-id
 Type=notify
 NotifyAccess=all

 [Install]
 WantedBy=default.target

7. Stop and delete the source container rootless-container using the stop and rm subcommands:

 [conuser1@server30 ~]$ podman stop rootless-container
 rootless-container

 [conuser1@server30 ~]$ podman rm rootless-container
 rootless-container

Verify the removal by running podman ps -a:

 [conuser1@server30 ~]$ podman ps -a
 CONTAINER ID  IMAGE       COMMAND     CREATED      STATUS      PORTS       NAMES

8. Update systemd to bring the new service to its control

 [conuser1@server30 ~]$ systemctl --user daemon-reload

9. Enable and start the container service:

 [conuser1@server30 ~]$ systemctl --user enable --now rootless-container.service 
 Created symlink  /home/conuser1/.config/systemd/user/default.target.wa nts/rootless-container.service →  /home/conuser1/.config/systemd/user/rootless- container.service.

10. Check the running status of the new service:

 conuser1@server30 ~]$ systemctl --user status  rootless-container
 rootless-container.service - Podman container- rootless-container>
     Loaded: loaded (/home/conuser1/.config/systemd/user/rootless->
     Active: active (running)

11. Verify the launch of a new container (compare the container ID with that of the source rootless container):

 [conuser1@server30 ~]$ podman ps
 CONTAINER ID  IMAGE                                   COMMAND     CREATED             STATUS              PORTS       NAMES
 57f946085605  registry.access.redhat.com/ubi8:latest  /bin/bash   About a minute ago  Up About a minute              rootless-container

12. Enable the container service to start and stop with host transition using the loginctl command (systemd login manager) and confirm:

 [conuser1@server30 ~]$ loginctl enable-linger
 [conuser1@server30 ~]$ loginctl show-user conuser1 | grep -i linger
 Linger=yes

13. Restart the container service using the systemctl command:

 [conuser1@server30 ~]$ systemctl --user restart  rootless-container
 [conuser1@server30 ~]$ systemctl --user status  rootless-container
 rootless-container.service - Podman container- rootless-container>
     Loaded: loaded  (/home/conuser1/.config/systemd/user/rootless->
     Active: active (running)

14. Check the status of the container again. Observe the removal of the previous container and the launch of a new container (compare container IDs).

 [conuser1@server30 ~]$ podman ps
 CONTAINER ID  IMAGE                                   COMMAND     CREATED         STATUS         PORTS       NAMES
 4dec33db41b5  registry.access.redhat.com/ubi8:latest  /bin/bash   41 seconds ago  Up 41 seconds              rootless-container
  • Each time the rootless-container service is restarted or server20 is rebooted, a new container will be launched. You can verify this by comparing their container IDs.

Containers DIY Labs

Lab: Launch Named Root Container with Port Mapping

  • Create a new user account called conadm on server30 and give them full sudo rights.
 [root@se

 -bash: 3: command not found
 rver30 ~]# adduser conadm
 [root@server30 ~]# visudo
 conadm ALL=(ALL)        ALL
  • As conadm with sudo (where required) on server30, inspect the latest version of ubi9 and then download it to your computer.
 [root@server30 ~]# dnf install container-tools
 [root@server30 ~]# podman login registry.redhat.io
 [conuser1@server30 ~]$ podman pull ubi9
 Resolved "ubi9" as an alias  (/etc/containers/registries.conf.d/001-rhel- shortnames.conf)
 Trying to pull  registry.access.redhat.com/ubi9:latest...
 Getting image source signatures
 Checking if image destination supports signatures
 Copying blob cc296d75b612 done   | 
 Copying config 159a1e6731 done   | 
 Writing manifest to image destination
 Storing signatures  159a1e67312ef50059357047ebe2a365afea904504fca9561abb3 85ecd942d62
 [conuser1@server30 ~]$ podman inspect ubi9
  • Launch a container called rootful-cont-port in attached terminal mode with host port 80 mapped to container port 8080.
 sudo podman run -it --name rootful-cont-port -p  80:8080 ubi9
  • Run a few basic Linux commands such as ls, pwd, df, cat /etc/redhat-release, and os-release while in the container.
 [root@349163a6e431 /]# ls
 afs  boot  etc	 lib	lost+found  mnt  proc  run    srv  tmp  var
 bin  dev   home  lib64	media	    opt  root  sbin   sys  usr

 [root@349163a6e431 /]# pwd
 /

 [root@349163a6e431 /]# df -hT
 Filesystem     Type      Size  Used Avail Use%  Mounted on
 overlay        overlay    17G  4.3G   13G  26% /
 tmpfs          tmpfs      64M     0   64M   0% /dev
 shm            tmpfs      63M     0   63M   0%  /dev/shm
 tmpfs          tmpfs     356M  6.0M  350M   2%  /etc/hosts
 devtmpfs       devtmpfs  4.0M     0  4.0M   0%  /proc/keys

 [root@349163a6e431 /]# cat /etc/redhat-release
 Red Hat Enterprise Linux release 9.4 (Plow)
  • Check to confirm the port mapping from server30.
 [conadm@server30 ~]$ sudo podman port rootful-cont- port
 8080/tcp -> 0.0.0.0:80
  • Do not remove the container yet.

Lab: Launch Nameless Rootless Container with Two Variables

  • As conadm on server30, launch a container using the latest version of ubi8 in interactive mode (-it) with two environment variables VAR1=lab1 and VAR2=lab2 defined.
 [conadm@server30 ~]$ podman run -d -e VAR1="lab1" -e VAR2="lab2" --name variables8 ubi8
  • Check the variables from within the container.
 [root@803642faea28 /]# echo $VAR1
 lab1
 [root@803642faea28 /]# echo $VAR2
 lab2
  • Delete the container and the image when done.

Lab: Launch Named Rootless Container with Persistent Storage

  • As conadm with sudo (where required) on server30, create a directory called /host_perm1 with full permissions, and a file called str1 in it.
 [conadm@server30 ~]$ sudo mkdir /host_perm1
 [sudo] password for conadm: 
 [conadm@server30 ~]$ sudo chmod 777 /host_perm1
 [conadm@server30 ~]$ sudo touch /host_perm1/str1
  • Launch a container called rootless-cont-str in attached terminal mode with the created directory mapped to /cont_perm1 inside the container.
 [conadm@server30 ~]$ sudo podman run --name  rootless-cont-str -v /host_perm1:/cont_perm1:Z -it  ubi8
 [root@a1326200eae1 /]#
  • While in the container, check access to the directory and the presence of the file.
 [root@a1326200eae1 /]# ls /cont_perm1
 str1
  • Create a sub-directory and a file under /cont_perm1 and exit out of the container shell.
 [root@a1326200eae1 cont_perm1]# mkdir permdir2
 [root@a1326200eae1 cont_perm1]# ls
 permdir2  str1
 [root@a1326200eae1 cont_perm1]# exit
 exit
 [conadm@server30 ~]$
  • List /host_perm1 on server30 to verify the sub-directory and the file.
 [conadm@server30 ~]$ sudo ls /host_perm1
 permdir2  str1
  • Stop and delete the container.
 [conadm@server30 ~]$ podman stop rootless-cont-str
 rootless-cont-str
 [conadm@server30 ~]$ podman rm rootless-cont-str
 rootless-cont-str
  • Remove /host_perm1.
 [conadm@server30 ~]$ sudo rm -r /host_perm1

Lab: Launch Named Rootless Container with Port Mapping, Environment Variables, and Persistent Storage

  • As conadm with sudo (where required) on server30, launch a named rootless container called rootless-cont-adv in attached mode with two variables (HISTSIZE=100 and MYNAME=RedHat), host port 9000 mapped to container port 8080, and /host_perm2 mounted at /cont_perm2
 [conadm@server30 ~]$ podman run --name rootless-cont-adv -v ~/host_perm2:/cont_perm2:Z -e HISTSIZE="100" -e MYNAME="RedHat" -p 9000:8080 -it --replace ubi8
 [root@79e965cd1436 /]#
  • Check and confirm the settings while inside the container.
 [root@79e965cd1436 /]# echo $HISTSIZE
 100

 [root@79e965cd1436 /]# echo $MYNAME
 RedHat

 [root@79e965cd1436 /]# ls -ld /cont_perm2 
 drwxrwxrwx. 2 root root 6 Aug  4 02:16 /cont_perm2

 [conadm@server30 ~]$ podman port rootless-cont-adv
 8080/tcp -> 0.0.0.0:9000
  • Exit out of the container.
 [root@5d510a1b2293 /]# exit
 exit
 [conadm@server30 ~]$
  • Do not remove the container yet.

Lab 22-5: Control Rootless Container States via systemd

  • As conadm on server30, use the rootless-cont-adv container launched in the last lab as a template and generate a systemd service configuration file and store the file in the appropriate directory.
 [conadm@server30 ~]$ podman run --name rootless-cont-adv -v ~/host_perm2:/cont_perm2:Z -e HISTSIZE="100" -e MYNAME="RedHat" -p 9000:8080 -dt --replace ubi8
 da8faf434813242985b8e332dc06b0e6da78e7125bc36579ffc8d82b0bcafb8e
 [conadm@server30 ~]$ podman generate systemd --new --name rootless-cont-adv >  ~/.config/systemd/user/rootless-container.service

 DEPRECATED command:
 It is recommended to use Quadlets for running  containers and pods under systemd.

 Please refer to podman-systemd.unit(5) for details.
  • Stop and remove the source container rootless-cont-adv.
 [conadm@server30 ~]$ podman stop rootless-cont-adv
 rootless-cont-adv
 [conadm@server30 ~]$ podman rm rootless-cont-adv
 rootless-cont-adv
  • Add the support for the new service to systemd and enable the new service to auto-start at system reboots.
 [conadm@server30 ~]$ systemctl --user daemon-reload

 [conadm@server30 user]$ systemctl --user enable -- now rootless-container.service
 Created symlink  /home/conadm/.config/systemd/user/default.target.want s/rootless-container.service →  /home/conadm/.config/systemd/user/rootless- container.service.
  • Perform the required setup to ensure the container is launched without the need for the conadm user to log in.
 [conadm@server30 user]$ loginctl enable-linger

 [conadm@server30 user]$ loginctl show-user conadm |  grep -i linger
 Linger=yes
  • Reboot server30 and confirm a successful start of the container service and the container.
[root@rhcsa3 ~]# systemctl --user --machine=conadm@ list-units --type=service
  UNIT                           LOAD   ACTIVE SUB     DESCRIPTION           >
  dbus-broker.service            loaded active running D-Bus User Message Bus
  rootless-cont-adv.service      loaded active running Podman container-rootl>
  systemd-tmpfiles-setup.service loaded active exited  Create User's Volatile>

LOAD   = Reflects whether the unit definition was properly loaded.
ACTIVE = The high-level unit activation state, i.e. generalization of SUB.
SUB    = The low-level unit activation state, values depend on unit type.
3 loaded units listed. Pass --all to see loaded but inactive units, too.
To show all installed unit files use 'systemctl list-unit-files'.
[root@rhcsa3 ~]# sudo -i -u conadm podman ps -a
CONTAINER ID  IMAGE                                   COMMAND     CREATED         STATUS         PORTS                   NAMES
a48fd2c25be4  registry.access.redhat.com/ubi9:latest  /bin/bash   10 minutes ago  Up 10 minutes  0.0.0.0:9000->8080/tcp  rootless-cont-adv

Lab 22-6: Control Rootful Container States via systemd

  • As conadm with sudo where required on server10, use the rootful-cont-port container launched in Lab 22-1 as a template and generate a systemd service configuration file and store the file in the appropriate directory.
 [root@server30 ~]# podman generate systemd --new -- name rootful-cont-port | tee  /etc/systemd/system/rootful-cont-port.service
 DEPRECATED command:
 It is recommended to use Quadlets for running  containers and pods under systemd.

 Please refer to podman-systemd.unit(5) for details.
 # container-rootful-cont-port.service
 # autogenerated by Podman 4.9.4-rhel
 # Sat Aug  3 20:49:32 MST 2024

 [Unit]
 Description=Podman container-rootful-cont- port.service
 Documentation=man:podman-generate-systemd(1)
 Wants=network-online.target
 After=network-online.target
 RequiresMountsFor=%t/containers

 [Service]
 Environment=PODMAN_SYSTEMD_UNIT=%n
 Restart=on-failure
  TimeoutStopSec=70
 ExecStart=/usr/bin/podman run \
	--cidfile=%t/%n.ctr-id \
	--cgroups=no-conmon \
	--rm \
	--sdnotify=conmon \
	-d \
	--replace \
	-it \
	--name rootful-cont-port \
	-p 80:8080 ubi9
 ExecStop=/usr/bin/podman stop \
	--ignore -t 10 \
	--cidfile=%t/%n.ctr-id
 ExecStopPost=/usr/bin/podman rm \
	-f \
	--ignore -t 10 \
	--cidfile=%t/%n.ctr-id
 Type=notify
 NotifyAccess=all

 [Install]
 WantedBy=default.target
  • Stop and remove the source container rootful-cont-port.
 [root@server30 ~]# podman stop rootful-cont-port
 WARN[0010] StopSignal SIGTERM failed to stop  container rootful-cont-port in 10 seconds, resorting  to SIGKILL 
 rootful-cont-port
 [root@server30 ~]# podman ps
 CONTAINER ID  IMAGE                                   COMMAND     CREATED         STATUS         PORTS       NAMES
 fe0d07718dda  registry.access.redhat.com/ubi9:latest  /bin/bash   16 minutes ago  Up 16 minutes              rootful-container
 [root@server30 ~]# podman rm rootfil-cont-port
 Error: no container with ID or name "rootfil-cont- port" found: no such container
 [root@server30 ~]# podman rm rootful-cont-port
 rootful-cont-port
  • Add the support for the new service to systemd and enable the service to auto-start at system reboots.
 [root@server30 ~]# systemctl daemon-reload
 [root@server30 ~]# systemctl enable --now rootful- cont-port
 Created symlink  /etc/systemd/system/default.target.wants/rootful- cont-port.service → /etc/systemd/system/rootful-cont- port.service.
  • Reboot server10 and confirm a successful start of the container service and the container.
 [root@server30 ~]# reboot

 [root@server30 ~]# podman ps
 CONTAINER ID  IMAGE                                   COMMAND     CREATED             STATUS              PORTS                 NAMES
 5c030407a7d6   registry.access.redhat.com/ubi9:latest  /bin/bash    About a minute ago  Up About a minute  0.0.0.0:80- >8080/tcp  rootful-cont-port
 9d1e8a429ac6   registry.access.redhat.com/ubi9:latest  /bin/bash    About a minute ago  Up About a minute                        rootful-container
 [root@server30 ~]#

Lab 22-7: Build Custom Image Using Containerfile

  • As conadm on server10, write a containerfile to use the latest version of ubi8 and create a user account called user-in-container in the resultant custom image.
 [conadm@server30 ~]$ vim containerfile
 FROM registry.access.redhat.com/ubi8/ubi:latest

 RUN useradd -ms /bin/bash -u 1001 user-in-container

 USER 1001
 [conadm@server30 ~]$ podman image build -f  containerfile --no-cache -t ubi8-user .
 STEP 1/3: FROM  registry.access.redhat.com/ubi8/ubi:latest
 STEP 2/3: RUN useradd -ms /bin/bash -u 1001 user-in- container
 --> b330095e91eb
 STEP 3/3: USER 1001
 COMMIT ubi8-user
 --> e8cde30fc020
 Successfully tagged localhost/ubi8-user:latest
 e8cde30fc020051caa2a4e2f58aaaf90f088709462a1314b936fd608facfdb5e
  • Test the image by launching a container in interactive mode and verifying the user.
 [conadm@server30 ~]$ podman run -ti --name test12  ubi8-user
 [user-in-container@30558ffcb227 /]$