In this article, our Support team provides us with a brief introduction on Docker yml depends_on.

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Let’s take a closer look at Docker compose depends_on option.

What is Docker yml depends_on?

Docker yml: Compose is a Docker application that allows us to define and run multi-container Docker applications. Compose also allows us to configure the application’s services using a YAML file. Additionally, Compose includes commands for managing the application’s entire lifecycle.

• To start, stop, and rebuild services.
• To view the status of currently running services.
• To stream the log output of currently running services.
• To execute a one-time command on a service.

depends_on: Docker yml depends_on express dependency between services. The depends_on option allows specifying the order in which services start and stop. The depends_on, links, volumes_from, and network_mode: “service:…” option in the compose determines the dependencies. Also, compose always starts and stops containers in dependency order. Service dependencies results in the following behaviors:

• docker-compose up starts services in dependency order. In the following example, DB and redis will start before the web.
• docker-compose up naturally includes service’s dependencies. In the example below, docker-compose up web creates and starts db and redis.
• docker-compose terminates services in order of dependency. In the following example, web terminates before db and redis.

Docker yml depends_on: An example

version: "3.9"
services:
  web:
    build: .
    depends_on:
      - db
      - redis
  redis:
    image: redis
  db:
    image: postgres

When using depends_on, keep the following in mind:

1. The depends_on only waits until db and redis have been started; it does not wait for them to be “ready” before starting the web.
2. The depends_on option is not taken to account when deploying a stack in swarm mode with a version 3 Compose file.

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Conclusion

With the Docker yml depends_on option, we can control the order of service startup and shutdown. To conclude, our Expert team went over the Docker yml depends_on details.