Docker - Run Container from Inside Container

Question

I have two applications:

• a Python console script that does a short(ish) task and exits
• a Flask "frontend" for starting the console app by passing it command line arguments

Currently, the Flask project carries a copy of the console script and runs it using subprocess when necessary. This works great in a Docker container but they are too tightly coupled. There are situations where I'd like to run the console script from the command line.

I'd like to separate the two applications into separate containers. To make this work, the Flask application needs to be able to start the console script in a separate container (which could be on a different machine). Ideally, I'd like to not have to run the console script container inside the Flask container, so that only one process runs per container. Plus I'll need to be able to pass the console script command line arguments.

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Q: How can I spawn a container with a short lived task from inside a container?

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Answer 1

You can just give the container access to execute docker commands. It will either need direct access to the docker socket or it will need the various tcp environment variables and files (client certs, etc). Obviously it will need a docker client installed on the container as well.

A simple example of a container that can execute docker commands on the host:

docker run -v /var/run/docker.sock:/var/run/docker.sock your_image

It's important to note that this is not the same as running a docker daemon in a container. For that you need a solution like jpetazzo/dind.