docker - Is it possible to start a stopped container from another container

Question

There are two containers A and B. Once container A starts, one process will be executed, then the container will stop. Container B is just an web application (say expressjs). Is it possible to kickstart A from container B ?

Answer 1

It is possible to grant a container access to docker so that it can spawn other containers on your host. You do this by exposing the docker socket inside the container, e.g:

docker run -v /var/run/docker.sock:/var/run/docker.sock --name containerB myimage ...

Now, if you have the docker client available inside the container, you will be able to control the docker daemon on your host and use that to spawn your "container A".

Before trying this approach, you should be aware of the security considerations: access to docker is the same as having root access on the host, which means if your web application has a remote compromise you have just handed the keys to your host to the attackers. This is described more fully in this article.