7장. 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
참고

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.

7.1. Using the UBI init images

You can build a container by 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 by 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

  1. Create a Containerfile with the following contents to a new directory:

    FROM registry.access.redhat.com/ubi10/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" ]

    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.

  2. Build the container:

    # podman build --format=docker -t mysysd .
  3. 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:

    # setsebool -P container_manage_cgroup 1
  4. Run the container named mysysd_run:

    # podman run -d --name=mysysd_run -p 80:80 mysysd

    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.

    참고

    In rootless mode, you have to choose host port number >= 1024. For example:

    $ podman run -d --name=mysysd -p 8081:80 mysysd

    To use port numbers < 1024, you have to modify the net.ipv4.ip_unprivileged_port_start variable:

    # sysctl net.ipv4.ip_unprivileged_port_start=80
  5. Check that the container is running:

    # podman ps
    a282b0c2ad3d  localhost/mysysd:latest  /sbin/init  15 seconds ago  Up 14 seconds ago  0.0.0.0:80->80/tcp  mysysd_run
  6. Test the web server:

    # curl localhost/index.html
    Successful Web Server Test
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