What is the alternative to condition form of depen

Question

docker-compose 2.1 offers the nice feature to specify a condition with depends_on. The current docker-compose documentation states:

Version 3 no longer supports the condition form of depends_on.

Unfortunately the documentation does not explain, why the condition form was removed and is lacking any specific recommondation on how to implement that behaviour using V3 upwards.

Answer 1

There's been a move away from specifying container dependencies in compose. They're only valid at startup time and don't work when dependent containers are restarted at run time. Instead, each container should include mechanism to retry to reconnect to dependent services when the connection is dropped. Many libraries to connect to databases or REST API services have configurable built-in retries. I'd look into that. It is needed for production code anyway.

Answer 2

There are some external tools that let you mimic this behaviour. For example, with the dockerize tool you can wrap your CMD or ENTRYPOINT with dockerize -wait and that will prevent running your application until specified services are ready.

If your docker-compose file used to look like this:

version: '2.1'
services:
  kafka:
    image: spotify/kafka
    healthcheck:
      test: nc -z localhost 9092
  webapp:
     image: foo/bar # your image
     healthcheck:
       test: curl -f http://localhost:8080
  tests:
     image: bar/foo # your image
     command: YOUR_TEST_COMMAND
     depends_on:
       kafka:
         condition: service_healthy
       webapp:
         condition: service_healthy

then you can use dockerize in your v3 compose file like this:

version: '3.0'
services:
  kafka:
    image: spotify/kafka
  webapp:
     image: foo/bar # your image
  tests:
     image: bar/foo # your image
     command: dockerize -wait tcp://kafka:9092 -wait web://webapp:8080 YOUR_TEST_COMMAND