docs/content/compose/startup-order.md

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How to control service startup and shutdown order in Docker Compose	documentation, docs, docker, compose, startup, shutdown, order	Control startup and shutdown order in Compose	true

You can control the order of service startup and shutdown with the depends_on attribute. Compose always starts and stops containers in dependency order, where dependencies are determined by depends_on, links, volumes_from, and network_mode: "service:...".

A good example of when you might use this is an application which needs to access a database. If both services are started with docker compose up, there is a chance this will fail since the application service might start before the database service and won't find a database able to handle its SQL statements.

Control startup

On startup, Compose does not wait until a container is "ready", only until it's running. This can cause issues if, for example, you have a relational database system that needs to start its own services before being able to handle incoming connections.

The solution for detecting the ready state of a service is to use the condition attribute with one of the following options:

• service_started
• service_healthy. This specifies that a dependency is expected to be “healthy”, which is defined with healthcheck, before starting a dependent service.
• service_completed_successfully. This specifies that a dependency is expected to run to successful completion before starting a dependent service.

Example

services:
  web:
    build: .
    depends_on:
      db:
        condition: service_healthy
        restart: true
      redis:
        condition: service_started
  redis:
    image: redis
  db:
    image: postgres
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER} -d ${POSTGRES_DB}"]
      interval: 10s
      retries: 5
      start_period: 30s
      timeout: 10s

Compose creates services in dependency order. db and redis are created before web.

Compose waits for healthchecks to pass on dependencies marked with service_healthy. db is expected to be "healthy" (as indicated by healthcheck) before web is created.

The healthcheck for the db service uses the pg_isready -U ${POSTGRES_USER} -d ${POSTGRES_DB}' command to check if the PostgreSQL database is ready. The service is retried every 10 seconds, up to 5 times.

Compose also removes services in dependency order. web is removed before db and redis.

Reference information

• depends_on
• healthcheck