Control startup and shutdown order in Compose
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 withhealthcheck
, 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
.