5.4. Building a container

Prerequisites

1. The container-tools meta-package is installed.

Procedure

1. Install Container Tools: Ensure the necessary container tools are installed on your RHEL system. The container-tools module provides Buildah, Podman, and Skopeo.

   $ sudo dnf install container-tools

2. Create a Containerfile: A Containerfile defines the instructions for building your container image. This file specifies the base image, any software to install, configurations to apply, and the application to run. For example:

   FROM registry.redhat.io/ubi10/ubi-minimal
   RUN microdnf -y update && microdnf -y install
   COPY index.html /var/www/html/
   EXPOSE 80
   CMD ["httpd", "-DFOREGROUND"]

3. Build the container image with Buildah: Use buildah bud (or podman build) to build the image after you navigate to the directory containing your Container file.

   $ cd /<path_to_container_file>
   
   $ buildah bud -t your_image_name:tag .

   • your_image_name: The name for your image.
   • tag: The tag for your image (e.g., latest, 1.0).
   • .: Indicates that the Containerfile is in the current directory.

4. Run the container: After you build the image, you can run a container from it using the podman run command.

   $ podman run -d -p 8080:80 my-web-app

   • -d: Runs the container in detached mode (in the background).
   • -p 8080:80: Maps port 8080 on the host to port 80 inside the container.

   • my-web-app: The name of the image to run.

     The heredocs syntax in container buildings

     You can use the heredoc syntax in Containerfile, with a Red Hat Enterprise Linux base image, ensuring you enable BuildKit. If the commands contain heredoc syntax, the Containerfile considers the next lines, until the line only contains a heredoc delimiter, as part of the same command. You can embed multi-line strings directly within instructions like RUN or COPY in Containerfile using heredocs. This is especially useful with RHEL-based images, as it removes the need to create separate script files for simple tasks and thus improves readability and maintainability.

     For Example, a common use case is running multiple shell commands in a single RUN instruction to create a single image layer, avoiding the && \ syntax: