How to add a default env var to all docker containers

Question

I am trying to configure my dockerd to inject an env var into all containers that it starts.

More specifically, I need every container to use SSH for it's DOCKER_HOST and also where that host is, so that containers don't try to volume mount the docker unix socket with -v /var/docker/docker.sock:/var/sock/docker.sock because that's a command that needs to be restricted

So, the general question (inject ANY env var to all containers) would be useful, but specifically, I need to inject the DOCKER_HOST, which might have a non generalized answer

Answer 1

To the best of my knowledge there is no native facility for injecting a set of default environment variables into all Docker containers; see Moby issue #16699 for some thoughts on exactly this question.

I guess if you were really ambitious, you could write a mutating proxy that sits in front of the docker socket and have it intercept the ContainerCreate operation, Update the Env key, and pass the request on to Docker.