xenoscopic / depends-on-condition

An Example of Using depends_on: condition in a Compose Project

depends_on: condition

This project contains an example of using the condition form of depends_on in Compose projects. This functionality was recently revived as part of the Compose Spec and requires Docker Compose v1.27.0+.

This project grew out of a talk given at the Docker Community All Hands meeting on 11 March 2021.

Design

There are two services: describer and web. web is defined to have a dependency on describer (using the condition: service_healthy form of depends_on), so Compose waits for describer to start and become healthy before starting web.

The describer service has a simulated startup time of 10 seconds and a health check defined that dependent services can use to wait on. The web service has a simulated hard dependency on the describer service, exiting if the latter isn't available immediately when web starts.

Usage

To run the project, use:

docker-compose up --build

After the describer service starts, you'll see the project wait for about 10 seconds while it waits for the service to become healthy. After that, the web service will start and be available on http://localhost:8080.

Refresh the page repeatedly for inspirational messages (and to ensure that the services are communicating).

To tear down the project, use:

docker-compose down --rmi=local