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Linux distributions for containers

Repo Man

Article from ADMIN 33/2016

By Thorsten Scherf

When operating multiple containers in an environment, you need to use special Linux distributions as a base, such as CoreOS or Red Hat Atomic. We show you how to add applications to and create a custom Atomic software repository for the base system.

CoreOS and Atomic are two major Linux distributions optimized for containers and available in the enterprise environment. Not only are these distributions hardened accordingly and suitable for providing the run-time environment for Docker containers, but the entire scope of the distribution has been reduced to a minimum, because these hosts are only intended to operate containers, not to activate any other services.

This rather well-intentioned idea causes problems in many environments, however, such as when you need monitoring or backup software, change management tools, or other applications on the system. Unfortunately, it isn't always easy to install the required software packages after the fact. In this article, I explain why this is the case and how to install the required software on your Docker hosts.

An Atomic installation is used as an example. Corresponding operating system images exist for both Red Hat Enterprise Linux and its community variants CentOS and Fedora. I use a Fedora image [1] that serves as the basis for setting up a KVM-based virtual machine that can be made available within a very short span of time using the virt-manager or virt-install tools. On top of that, I take a regular Fedora 22 system, generate a custom Atomic software repository, and fill it with the desired packages. Docker hosts can then use this custom repository.

Atomic with a Package Manager

At this point, some readers might already be wondering why all this effort is necessary. After all, it's usual with RPM-based distributions to be able to install software packages from corresponding repositories using a package manager. However, it's different with Atomic, because it has no package manager. Instead, such hosts use completely prefabricated filesystem trees that are loaded onto the local host from a central

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