Remote Docker Contexts

Despite being a Docker user for years now, I recently learned about a killer feature called Docker Contexts which allows the docker cli to target different nodes or clusters. This seems like a great addition to tools like code-server and projector to do development on a remote server.

Remote Host Setup

Setup is simple - to start, make sure that the remote host has docker installed.

Client Machine Setup

Make sure your client machine (the machine where you’re going to be running the docker cli) has passwordless ssh setup to the remote host. Now, you’re ready to create a new docker context.

[~]$ docker context create contextname --docker "host=ssh://username@remotehostname"
contextname
Successfully created context "contextname"
[~]$ docker context use contextname
contextname

That’s it! Your docker cli is now pointing to your remote host.

Testing it Out

If you now run a docker command, it will be executed on the remote host.

# Client Machine
[~]$ docker run hello-world

# Remote Host
[~]$ docker ps
CONTAINER ID   IMAGE         COMMAND    CREATED              STATUS                          PORTS     NAMES
1bee29c20474   hello-world   "/hello"   About a minute ago   Exited (0) About a minute ago             strange_torvalds

Other Commands

You can use docker context ls to get a list of all the contexts on your machine.

Limitations

It’s worth nothing that if you specify volumes that are mapped on the client machine, they of course will not be available on the remote machine and thus will not work. This means that you’ll need to ensure that volume paths refer to the remote machine - which in retrospect seems pretty obvious.