I have 2 services that are very similar. I have seen that it is a common practice to give a variable name to one service configuration and use it and extend it in your specific services' configurations.
services:
backend: &backend
build:
context: .
dockerfile: ./docker/app/DockerFile
volumes:
- .:/var/www/apps
app:
<<: *backend
ports:
- 127.0.0.1:3000:3000
depends_on:
- db
- dashboard_db
- redis
- sidekiq
sidekiq:
<<: *backend
depends_on:
- redis
command: bundle exec sidekiq
The problem is that when I execute docker compose up the service backend is also up and running, but in my case, I only want the specific services (app and sidekiq) to be up.
Am I using the &variable syntax properly?
This is YAML anchor syntax. This is syntactically correct as you've shown it. Attaching an anchor to a YAML node doesn't cause it to be removed from its parent, though: in the Compose data model, there are three services including backend, and docker-compose up will start all of them.
The Compose file format allows extension sections (similarly in Compose file format version 3). If you put the anchored object under some other top-level field that isn't services: and starts with x-, then it'll be included in the YAML data model, but Compose won't independently recognize it as a service.
version: '3.8'
x-service-templates: # add this new section
backend: &backend
build:
context: .
dockerfile: ./docker/app/DockerFile
volumes:
- .:/var/www/apps
services:
# same as above
app:
<<: *backend
ports: ['127.0.0.1:3000:3000']
depends_on: [db, dashboard_db, redis, sidekiq]
sidekiq:
<<: *backend
depends_on: [redis]
command: bundle exec sidekiq