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Docker-Compose - Wait for Dependencies

Posted Updated
By Ashim Khadka
2 min read
Docker-Compose - Wait for Dependencies

Don't Repeat Yourself for sake of others. So, there is nothing new in here, that hasn’t been elaborated on by many other authors. I am just noting it down and extracting major parts of it.

So, let’s wait for the docker dependencies…

If we run docker-compose.yml then waiting-for-rabbitmq will print Waiting for rabbitmq... until rabbitmq starts. Sometimes it’s expected behavior but not for us.

There are many ways to resolve it and we will look into this one by one.

Approach 1: Run the dependencies first

First, we will run the dependency along with its status checker service. Once the status is green, then we will run all the other dependent services.

Let’s create a scenario, where we will have a web service that will depend on rabbitmq. Now we will add another service in the docker-compose.yml file, which is like this.

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services:
  rabbitmq:
    container_name: ajk_rabbitmq
    image: rabbitmq:3.7-management-alpine
    ports:
      - 5672:5672
      - 15672:15672

  web:
    container_name: ajk_web
    image: alpine:3.8
    command: [ 'sh', '-c', 'nc -z -v rabbitmq 5672' ]
    depends_on:
      - rabbitmq
    links:
      - rabbitmq

  waiting_for_rabbitmq:
    container_name: ajk_waiting_for_rabbitmq
    image: alpine:3.8
    command: [ 'sh', '-c', 'until nc -z -v rabbitmq 5672; do echo "Waiting for rabbitmq..." && sleep 1; done;' ]
    depends_on:
      - rabbitmq
    links:
      - rabbitmq

How to run

  • Run docker-compose up waiting_for_rabbitmq command
    • It will start rabbitmq service
    • waiting_for_rabbitmq service will wait for rabbitmq to be started
    • Once, it is started, it will print 5672 (IP:5672) open in the console
  • Now, run docker-compose up web

Although it’s a sequential approach it will do the work for us.

Reference:

Approach 2: Using health checks

When we run docker-compose.yml file, first it will run rabbitmq service, and will wait for its status to be healthy.

Once, it’s ready, web service will be started and will print the following in the console:

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ajk_web     | rabbitmq (172.22.0.2:5672) open
ajk_web       exited with code 0

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services:
  rabbitmq:
    container_name: ajk_rabbitmq
    image: rabbitmq:3.7-management-alpine
    ports:
      - 5672:5672
      - 15672:15672
    healthcheck:
      test: ["CMD", "nc", "-z", "localhost", "5672"]
      interval: 10s
      timeout: 10s
      retries: 3

  web:
    container_name: ajk_web
    image: alpine:3.8
    command: ["sh", "-c", "nc -z -v rabbitmq 5672"]
    depends_on:
      rabbitmq:
        condition: service_healthy
    links:
      - rabbitmq

Here, we are using healthcheck configuration option, added in rabbitmq service. web service is depending upon rabbitmq with the condition service_healthy.

Note: docker-compose version 3 doesn’t support the condition form of depends_on. We can add restart: on-failure in the web service to get the same behavior. One thing to keep in mind is, now web service will be restarted until rabbitmq status is healthy.

Reference:

Other ways to do it

docker-compose
development
This post is licensed under CC BY 4.0 by the author.