Chapter 7. Adding software to a UBI container
Chapter 7. Adding software to a UBI container Red Hat Universal Base Images (UBIs) are built from a subset of the RHEL content. UBIs also provide a subset of RHEL packages that are freely available to install for use with UBI. To add or update software to a running container, you can use the dnf repositories that include RPM packages and updates. UBIs provide a set of pre-built language runtime container images such as Python, Perl, Node.js, Ruby, and so on. To add packages from UBI repositories to running UBI containers: On UBI init and UBI standard images, use the dnf command On UBI minimal images, use the microdnf command Note Installing and working with software packages directly in running containers adds packages temporarily. The changes are not saved in the container image. To make package changes persistent, see section Building an image from a Containerfile with Buildah . Note When you add software to a UBI container, procedures differ for updating UBIs on a subscribed RHEL host or on an unsubscribed (or non-RHEL) system. 7.1. Using the UBI init images You can build a container using a Containerfile that installs and configures a Web server ( httpd ) to start automatically by the systemd service ( /sbin/init ) when the container is run on a host system. The podman build command builds an image using instructions in one or more Containerfiles and a specified build context directory. The context directory can be specified as the URL of an archive, Git repository or Containerfile . If no context directory is specified, then the current working directory is considered as the build context, and must contain the Containerfile . You can also specify a Containerfile with the --file option. Prerequisites The container-tools meta-package is installed. Procedure Create a Containerfile with the following contents to a new directory: The Containerfile installs the httpd package, enables the httpd service to start at boot time, creates a test file ( index.html ), exposes the Web server to the host (port 80), and starts the systemd init service ( /sbin/init ) when the container starts. Build the container: Optional: If you want to run containers with systemd and SELinux is enabled on your system, you must set the container_manage_cgroup boolean variable: Run the container named mysysd_run : The mysysd image runs as the mysysd_run container as a daemon process, with port 80 from the container exposed to port 80 on the host system. Note In rootless mode, you have to choose host port number >= 1024. For example: To use port numbers < 1024, you have to modify the net.ipv4.ip_unprivileged_port_start variable: Check that the container is running: Test the web server: Additional resources Shortcomings of Rootless Podman 7.2. Using the UBI micro images You can build a ubi-micro container image using the Buildah tool. Prerequisites The container-tools meta-package is installed. Prerequisites The podman tool, provided by the containers-tool meta-package, is installed. Procedure Pull and build the registry.access.redhat.com/ubi8/ubi-micro image: Mount a working container root filesystem: Install the httpd service to the micromount directory: Unmount the root file system on the working container: Create the ubi-micro-httpd image from a working container: Verification Display details about the ubi-micro-httpd image: 7.3. Adding software to a UBI container on a subscribed host If you are running a UBI container on a registered and subscribed RHEL host, the RHEL Base and AppStream repositories are enabled inside the standard UBI container, along with all the UBI repositories. Red Hat entitlements are passed from a subscribed Red Hat host as a secrets mount defined in /usr/share/containers/mounts.conf on the host running Podman. Verify the mounts configuration: The yum , dnf , and microdnf commands should search for entitlement data at this path. If the path is not present, the commands cannot use Red Hat entitled content, such as the RHV repositories, because they lack the keys or content access the host has. This is applicable only for Red Hat shipped or provided Podman on a RHEL host. If you installed Podman not shipped by Red Hat, see the Red Hat Knowledgebase solution How do I attach subscription data to containers running in Docker not provided by Red Hat? . 7.4. Adding software in a standard UBI container To add software inside the standard UBI container, disable non-UBI dnf repositories to ensure the containers you build can be redistributed. Prerequisites The container-tools meta-package is installed. Procedure Pull and run the registry.access.redhat.com/ubi9/ubi image: Add a package to the myubi container. To add a package that is in the UBI repository, disable all dnf repositories except for UBI repositories. For example, to add the bzip2 package: To add a package that is not in the UBI repository, do not disable any repositories. For example, to add the zsh package: To add a package that is in a different host repository, explicitly enable the repository you need. For example, to install the python38-devel package from the codeready-builder-for-rhel-8-x86_64-rpms repository: Verification List all enabled repositories inside the container: Ensure that the required repositories are listed. List all installed packages: Ensure that the required packages are listed. Note Installing Red Hat packages that are not inside the Red Hat UBI repositories can limit the ability to distribute the container outside of subscribed RHEL systems. 7.5. Adding software in a minimal UBI container UBI dnf repositories are enabled inside UBI Minimal images by default. Prerequisites The container-tools meta-package is installed. Procedure Pull and run the registry.access.redhat.com/ubi9/ubi-minimal image: Add a package to the myubimin container: To add a package that is in the UBI repository, do not disable any repositories. For example, to add the bzip2 package: To add a package that is in a different host repository, explicitly enable the repository you need. For example, to install the python38-devel package from the codeready-builder-for-rhel-8-x86_64-rpms repository: The --setopt install_weak_deps=false option disables the installation of weak dependencies. Weak dependencies include recommended or suggested packages that are not strictly required but are often installed by default. Verification List all enabled repositories inside the container: Ensure that the required repositories are listed. List all installed packages: Ensure that the required packages are listed. Note Installing Red Hat packages that are not inside the Red Hat UBI repositories can limit the ability to distribute the container outside of subscribed RHEL systems. 7.6. Adding software to a UBI container on a unsubscribed host You do not have to disable any repositories when adding software packages on unsubscribed RHEL systems. Prerequisites The container-tools meta-package is installed. Procedure Add a package to a running container based on the UBI standard or UBI init images. Do not disable any repositories. Use the podman run command to run the container. then use the dnf install command inside a container. For example, to add the bzip2 package to the UBI standard based container: For example, to add the bzip2 package to the UBI init based container: Verification List all enabled repositories: To list all enabled repositories inside the containers based on UBI standard or UBI init images: To list all enabled repositories inside the containers based on UBI minimal containers: Ensure that the required repositories are listed. List all installed packages: Ensure that the required packages are listed. 7.7. Building UBI-based images You can create a UBI-based web server container from a Containerfile using the Buildah utility. You have to disable all non-UBI dnf repositories to ensure that your image contains only Red Hat software that you can redistribute. Note For UBI minimal images, use microdnf instead of dnf : RUN microdnf update -y && rm -rf /var/cache/yum and RUN microdnf install httpd -y && microdnf clean all commands. Prerequisites The container-tools meta-package is installed. Procedure Create a Containerfile : Build the container image: Verification Run the web server: Test the web server: 7.8. Using Application Stream runtime images Runtime images based on Application Streams offer a set of container images that you can use as the basis for your container builds. Supported runtime images are Python, Ruby, s2-core, s2i-base, .NET Core, PHP. The runtime images are available in the Red Hat Container Catalog . Note Because these UBI images contain the same basic software as their legacy image counterparts, you can learn about those images from the Using Red Hat Software Collections Container Images guide . Additional resources Red Hat Container Catalog Red Hat Container Image Updates 7.9. Getting UBI container image source code Source code is available for all Red Hat UBI-based images in the form of downloadable container images. Source container images cannot be run, despite being packaged as containers. To install Red Hat source container images on your system, use the skopeo command, not the podman pull command. Source container images are named based on the binary containers they represent. For example, for a particular standard RHEL UBI 9 container registry.access.redhat.com/ubi9:8.1-397 append -source to get the source container image ( registry.access.redhat.com/ubi9:8.1-397-source ). Prerequisites The container-tools meta-package is installed. Procedure Use the skopeo copy command to copy the source container image to a local directory: Use the skopeo inspect command to inspect the source container image: Unpack all the content: Check the results: If the results are correct, the image is ready to be used. Note It could take several hours after a container image is released for its associated source container to become available. Additional resources skopeo-copy and skopeo-inspect man pages on your system
FROM registry.access.redhat.com/ubi9/ubi-init RUN dnf -y install httpd; dnf clean all; systemctl enable httpd; RUN echo "Successful Web Server Test" > /var/www/html/index.html RUN mkdir /etc/systemd/system/httpd.service.d/; echo -e '[Service]\nRestart=always' > /etc/systemd/system/httpd.service.d/httpd.conf EXPOSE 80 CMD [ "/sbin/init" ] podman build --format=docker -t mysysd . setsebool -P container_manage_cgroup 1 podman run -d --name=mysysd_run -p 80:80 mysysd podman run -d --name=mysysd -p 8081:80 mysysd sysctl net.ipv4.ip_unprivileged_port_start=80 podman ps a282b0c2ad3d localhost/mysysd:latest /sbin/init 15 seconds ago Up 14 seconds ago 0.0.0.0:80->80/tcp mysysd_run curl localhost/index.html Successful Web Server Test microcontainer=USD(buildah from registry.access.redhat.com/ubi9/ubi-micro) micromount=USD(buildah mount USDmicrocontainer) dnf install --installroot USDmicromount --releasever=/ --setopt install_weak_deps=false --setopt=reposdir=/etc/yum.repos.d/ --nodocs -y httpd dnf clean all --installroot USDmicromount buildah umount USDmicrocontainer buildah commit USDmicrocontainer ubi-micro-httpd podman images ubi-micro-httpd localhost/ubi-micro-httpd latest 7c557e7fbe9f 22 minutes ago 151 MB cat /usr/share/containers/mounts.conf /usr/share/rhel/secrets:/run/secrets podman run -it --name myubi registry.access.redhat.com/ubi9/ubi dnf install --disablerepo= * --enablerepo=ubi-8-appstream-rpms --enablerepo=ubi-8-baseos-rpms bzip2 dnf install zsh dnf install --enablerepo=codeready-builder-for-rhel-8-x86_64-rpms python38-devel dnf repolist rpm -qa podman run -it --name myubimin registry.access.redhat.com/ubi9/ubi-minimal microdnf install bzip2 --setopt install_weak_deps=false microdnf install --enablerepo=codeready-builder-for-rhel-8-x86_64-rpms python38-devel --setopt install_weak_deps=false microdnf repolist rpm -qa podman run -it --name myubi registry.access.redhat.com/ubi9/ubi dnf install bzip2 podman run -it --name myubimin registry.access.redhat.com/ubi9/ubi-minimal microdnf install bzip2 dnf repolist microdnf repolist rpm -qa FROM registry.access.redhat.com/ubi9/ubi USER root LABEL maintainer="John Doe" Update image RUN dnf update --disablerepo=* --enablerepo=ubi-8-appstream-rpms --enablerepo=ubi-8-baseos-rpms -y && rm -rf /var/cache/yum RUN dnf install --disablerepo=* --enablerepo=ubi-8-appstream-rpms --enablerepo=ubi-8-baseos-rpms httpd -y && rm -rf /var/cache/yum Add default Web page and expose port RUN echo "The Web Server is Running" > /var/www/html/index.html EXPOSE 80 Start the service CMD ["-D", "FOREGROUND"] ENTRYPOINT ["/usr/sbin/httpd"] buildah bud -t johndoe/webserver . STEP 1: FROM registry.access.redhat.com/ubi9/ubi:latest STEP 2: USER root STEP 3: LABEL maintainer="John Doe" STEP 4: RUN dnf update --disablerepo=* --enablerepo=ubi-8-appstream-rpms --enablerepo=ubi-8-baseos-rpms -y Writing manifest to image destination Storing signatures --> f9874f27050 f9874f270500c255b950e751e53d37c6f8f6dba13425d42f30c2a8ef26b769f2 podman run -d --name=myweb -p 80:80 johndoe/webserver bbe98c71d18720d966e4567949888dc4fb86eec7d304e785d5177168a5965f64 curl http://localhost/index.html The Web Server is Running skopeo copy docker://registry.access.redhat.com/ubi9:8.1-397-source dir:USDHOME/TEST Copying blob 477bc8106765 done Copying blob c438818481d3 done Writing manifest to image destination Storing signatures skopeo inspect dir:USDHOME/TEST { "Digest": "sha256:7ab721ef3305271bbb629a6db065c59bbeb87bc53e7cbf88e2953a1217ba7322", "RepoTags": [], "Created": "2020-02-11T12:14:18.612461174Z", "DockerVersion": "", "Labels": null, "Architecture": "amd64", "Os": "linux", "Layers": [ "sha256:1ae73d938ab9f11718d0f6a4148eb07d38ac1c0a70b1d03e751de8bf3c2c87fa", "sha256:9fe966885cb8712c47efe5ecc2eaa0797a0d5ffb8b119c4bd4b400cc9e255421", "sha256:61b2527a4b836a4efbb82dfd449c0556c0f769570a6c02e112f88f8bbcd90166", "sha256:cc56c782b513e2bdd2cc2af77b69e13df4ab624ddb856c4d086206b46b9b9e5f", "sha256:dcf9396fdada4e6c1ce667b306b7f08a83c9e6b39d0955c481b8ea5b2a465b32", "sha256:feb6d2ae252402ea6a6fca8a158a7d32c7e4572db0e6e5a5eab15d4e0777951e" ], "Env": null } cd USDHOME/TEST for f in USD(ls); do tar xvf USDf; done find blobs/ rpm_dir/ blobs/ blobs/sha256 blobs/sha256/10914f1fff060ce31388f5ab963871870535aaaa551629f5ad182384d60fdf82 rpm_dir/ rpm_dir/gzip-1.9-4.el8.src.rpm