Docker builds over SSH

Published on , 299 words, 2 minutes to read

Plan 9 clustering at home

While on stream today, SlyEcho pointed out that you can set DOCKER_HOST=ssh://... to have the Docker client seamlessly do builds and the like over SSH instead of using the local computer's Docker daemon. In the process of playing with this, I found the docker context command. This is cool as hell, it allows you to manage multiple Docker daemons the same way that you would with Kubernetes clusters.

For example, here's what it looks like by default on Linux:

$ docker context ls
NAME        DESCRIPTION                               DOCKER ENDPOINT               ERROR
default *   Current DOCKER_HOST based configuration   unix:///var/run/docker.sock

You can add contexts with the docker context create command, and also point those contexts to remote hosts over SSH:

docker context create \
  --docker host=ssh://cadey@pneuma \
  --description "Iustorum autem semita quasi lux splendens procedit et crescit usque ad perfectam diem" \
  pneuma

Then whenever you need to deal with the remote host for a command:

docker --context pneuma pull alpine:edge

You can set it as the default with docker context use:

docker context use pneuma

And then whenever you're doing something with Docker, it will seamlessly SSH into the machine pneuma, do the operation, and then return the result. This works for building and running containers too:

$ hostname
shiroko

$ docker run -it --rm --network host alpine:edge
# hostname
pneuma

This even works for tools like Earthly:

$ earthly +all
(...)

$ docker images
REPOSITORY                TAG                   IMAGE ID       CREATED         SIZE
ghcr.io/xe/site/bin       earthly               828d989bb3b3   2 minutes ago   263MB
ghcr.io/xe/site/patreon   latest                9d3e945e7d6f   2 minutes ago   23.8MB

This means that even though I've somehow broken the Docker desktop app on my gaming PC that I stream from, I can still use Docker via one of my homelab machines!

This is cool as hell!

Facts and circumstances may have changed since publication. Please contact me before jumping to conclusions if something seems wrong or unclear.

Tags: docker, ssh, devops