docker compose make sure postgres is ready before starting other service

Sometimes we want to start a service in docker compose after some dependency is ready. In this case, we want to wait for PostgreSQL.

The key here is healthcheck on the PostgreSQL

healthcheck:
test: [ "CMD-SHELL", "pg_isready -U postgres" ]
interval: 10s
timeout: 5s
retries: 5

and depends_on on the service

depends_on:
postgres:
condition: service_healthy

Full docker-compose.yaml

version: '3.8'
services:
postgres:
image: postgres:11.6-alpine
environment:
POSTGRES_USER: postgres
POSTGRES_PASSWORD: 12345
POSTGRES_DB: todo
ports:
- 5432:5432
healthcheck:
test: [ "CMD-SHELL", "pg_isready -U postgres" ]
interval: 10s
timeout: 5s
retries: 5
backend:
build: backend
environment:
DB_HOST: postgres
ports:
- 5000:5000
depends_on:
postgres:
condition: service_healthy
volumes:
postgres_volume: