version: "3"

name: hge-postgres-replicas

services:
  # The primary server, which supports reads and writes.
  postgres-primary:
    extends:
      service: postgres
      file: ../../../docker-compose/databases.yaml
    command:
      # for some reason this is necessary, even if we don't actually use an archive
      - "--archive_mode=on"
    volumes:
      - primary-data:/var/lib/postgresql/data
      # this script enables replication for all users
      - ./init-primary.sh:/docker-entrypoint-initdb.d/init-primary.sh:ro

  # Initializes the replica by creating a backup of the primary into the
  # replica's data directory, then marking it as "standby" by creating the
  # "standby.signal" file.
  init-replica:
    extends:
      service: postgres
      file: ../../../docker-compose/databases.yaml
    command: 
      - su
      - postgres
      - -c
      - |
        set -ex
        PGPASSWORD=password pg_basebackup --host=postgres-primary --username=postgres --no-password --pgdata=/var/lib/postgresql/data
        touch /var/lib/postgresql/data/standby.signal
    volumes:
      - replica-data:/var/lib/postgresql/data
    depends_on:
      postgres-primary:
        condition: service_healthy

  # The replica server, which streams writes from the primary, and supports reads.
  postgres-replica:
    extends:
      service: postgres
      file: ../../../docker-compose/databases.yaml
    command:
      - "--primary_conninfo=host=postgres-primary port=5432 user=postgres password=password options='-c wal_sender_timeout=5000'"
      - "--hot_standby=on"
    volumes:
      - replica-data:/var/lib/postgresql/data
    depends_on:
      postgres-primary:
        condition: service_started
      init-replica:
        condition: service_completed_successfully

volumes:
  primary-data:
  replica-data: