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Chapter 2. Building and testing RHEL bootable container images
The following procedures use Podman to build and test your container image. You can also use other tools, for example, OpenShift Container Platform. For more examples of configuring RHEL systems by using containers, see the rhel-bootc-examples repository.
Red Hat provides the rhel9/rhel-bootc container image as a Technology Preview. Technology Preview features provide early access to upcoming product innovations, enabling customers to test functionality and provide feedback during the development process. However, these features are not fully supported. Documentation for a Technology Preview feature might be incomplete or include only basic installation and configuration information. See Technology Preview Features Support Scope on the Red Hat Customer Portal for information about the support scope for Technology Preview features.
Figure 2.1. Building an image by using instructions from a Containerfile, testing the container, pushing an image to a registry, and sharing it with others
A general Containerfile structure is the following:
FROM registry.redhat.io/rhel9/rhel-bootc:latest RUN dnf -y install [software] [dependencies] && dnf clean all ADD [application] ADD [configuration files] RUN [config scripts]
The rhel-9-bootc container image reuses the OCI image format.
-
The
rhel-9-bootccontainer image ignores the container config section (Config) when it is installed to a system. -
The
rhel-9-bootccontainer image does not ignore the container config section (Config) when you run this image by using container runtimes such aspodmanordocker.
For example, the following commands in a Containerfile are ignored when the rhel-9-bootc image is installed to a system:
-
ENTRYPOINTandCMD(OCI:Entrypoint/Cmd): you can setCMD /sbin/initinstead. -
ENV(OCI:Env): change thesystemdconfiguration to configure the global system environment. -
EXPOSE(OCI:exposedPorts): it is independent of how the system firewall and network function at runtime. -
USER(OCI:User): configure individual services inside the RHEL bootable container to run as unprivileged users instead.
The available commands that are usable inside a Containerfile and a Dockerfile are equivalent.
Building custom rhel-bootc base images is not supported in this release.
2.1. Building a container image
Use the podman build command to build an image using instructions from a Containerfile.
Prerequisites
-
The
container-toolsmeta-package is installed.
Procedure
Create a
Containerfile:$ cat Containerfile FROM registry.redhat.io/rhel9/rhel-bootc:latest RUN dnf -y install cloud-init && \ ln -s ../cloud-init.target /usr/lib/systemd/system/default.target.wants && \ dnf clean allThis
Containerfileexample adds thecloud-inittool, so it automatically fetches SSH keys and can run scripts from the infrastructure and also gather configuration and secrets from the instance metadata. For example, you can use this container image for pre-generated AWS or KVM guest systems.Build the
<image>image by usingContainerfilein the current directory:$ podman build -t quay.io/<namespace>/<image>:<tag>
Verification
List all images:
$ podman images REPOSITORY TAG IMAGE ID CREATED SIZE localhost/<image> latest b28cd00741b3 About a minute ago 2.1 GB
Additional resources
2.2. Running a container image
Use the podman run command to run and test your container.
Prerequisites
-
The
container-toolsmeta-package is installed.
Procedure
Run the container named
mybootcbased on thequay.io/<namespace>/<image>:<tag>container image:$ podman run -it --rm --name mybootc quay.io/<namespace>/<image>:<tag> /bin/bash-
The
-ioption creates an interactive session. Without the-toption, the shell stays open, but you cannot type anything to the shell. -
The
-toption opens a terminal session. Without the-ioption, the shell opens and then exits. -
The
--rmoption removes thequay.io/<namespace>/<image>:<tag>container image after the container exits.
-
The
Verification
List all running containers:
$ podman ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 7ccd6001166e quay.io/<namespace>/<image>:<tag> /sbin/init 6 seconds ago Up 5 seconds ago mybootc
Additional resources
2.3. Pushing a container image to the registry
Use the podman push command to push an image to your own, or a third party, registry and share it with others. The following procedure uses the Red Hat Quay registry.
Prerequisites
-
The
container-toolsmeta-package is installed. - An image is built and available on the local system.
- You have created the Red Hat Quay registry. For more information see Proof of Concept - Deploying Red Hat Quay.
Procedure
Push the
quay.io/<namespace>/<image>:<tag>container image from your local storage to the registry:$ podman push quay.io/<namespace>/<image>:<tag>
Additional resources
