Control startup and shutdown order in Compose

Table of contents

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.

restart: true ensures that if db is updated or restarted due to an explicit Compose operation, for example docker compose restart, the web service is also restarted automatically, ensuring it re-establishes connections or dependencies correctly.

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