Which Docker base image should be used to install Apps in a container without any additional OS?

Question

I am running a Docker daemon on my GUEST OS which is CentOS. I want to install software services on top of that in an isolated manner and I do not need another OS image inside my Docker container.

I want to have a Docker container with just the additional binaries and libraries for the software application I am going to install.

Is there a "whiteglove/blank" base image in Docker I can use ? I want a very lean container that uses as a starting point what my GUEST OS has to offer. Is that possible ?

Answer 1

What you're asking for isn't possible out-of-the-box with Docker. Each Docker image has its own root filesystem, which needs to have some sort of OS installed.

Your options are:

1. Use a minimal base image, such as the BusyBox image. This will give you the absolute minimum you need to get a container running.

2. Use the CentOS base image, in which case your container will be running the same or very similar OS.

The reason Docker images are like this is because they're meant to be portable. Any Docker image is meant to run anywhere Docker is running, regardless of the operating system. This means that the Docker image must contain an entire root filesystem and OS installation.

What you can do if you need stuff from the host OS is share a directory using Docker volumes. However, this is generally meant to be used for mounting data directories, and it still necessitates the Docker image having an OS.

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That said, if you have a statically-linked binary that has absolutely no dependencies, it becomes easy to create a very minimal image. This is called a "microcontainer", and Go in particular is well-suited to producing these. Here is some further reading on microcontainers and how to produce them.

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One other option you could look into if all you want is the resource management part of containers is using lxc-execute, as described in this answer. But you lose out on all the other nice Docker features as well. Unfortunately, what you're trying to do is just not what Docker is built for.