docker-compose-watch

A way to watch and rebuild on change with docker-compose

This is a drop in script to replace docker-compose/docker compose. Copy docker-compose somewhere in your path (/usr/local/bin or something) where it will win. It delegates to docker compose.

Run docker-compose up --build --watch and then when you edit files in that directory the relevant images will be built & containers recreated.

Layer caching should mean that the builds are fast if nothing relevant has changed, and if the resulting image is unchanged then the container will not be restarted.

Dependencies:

• Depends on fswatch, you'll need to install that manually
• Uses compose v2, you'll need to install docker compose v2 manually if docker compose version doesn't currently work for you.

Known weaknesses:

• It just uses pwd rather than parsing the yaml to decide which contexts to use

• It’s pretty inefficient because it doesn’t know about .dockerignore - so a change to an ignored file results in the entire context being calculated and sent to the docker daemon, before docker then decides there’s nothing to do.

  NOTE - actually this is better than I had thought:

  1. Obviously .dockerignore is avaluated before sending to the context, so while changes in files matched by .dockerignore will trigger a rebuild they won't go to the context
  2. so long as you are using DOCKER_BUILDKIT=1 buildkit also evaluates the COPY statements in the Dockerfile before sending the context, so only relevant files are sent to the context

• All services will have their contexts sent to the docker daemon - it should be possible I think to limit this by knowing which service's context got changed...

TO DO

1. Handle -f links to dockerfiles - including multiple of them. Also handle docker-compose.override.yml.
2. Use a cli yaml parser to read the services.<service_name>.build or services.<service_name>.build.context from each service in each of these (depending on whether it's a string or an object) The context will likely be a relative path - if it is, it must be resolved relative to the first -f compose file
3. Listen to all of those context directories - should be possible in a single fswatch subprocess.
4. On change, work out which service(s) context(s) the change was in, and pass their names to docker compose up: docker compose up -d --build <service1> <service2> ...

I think that will produce something usable so long as you use DOCKER_BUILDKIT=1, have an appropriate .dockerignore & factor your Dockerfile for sensible layer caching, without going to the lengths of trying to calculate whether the change is excluded by a .dockerignore in bash.

Contributions / criticism welcome.