New volume created on each container startup

[krzychuz]

I do use fairly standard docker-compose file:

postgresql_backup:
    container_name: my-db-backup
    image: prodrigestivill/postgres-backup-local
    restart: always
    volumes:
        - /opt/db_backups/:/backups
    links:
        - postgresql_database
    depends_on:
        - postgresql_database
    environment:
        - POSTGRES_HOST=postgresql_database
        - POSTGRES_DB=my-db
        - POSTGRES_USER=user
        - POSTGRES_PASSWORD=password
        - POSTGRES_EXTRA_OPTS=-Z6 --schema=public --blobs
        - SCHEDULE=@daily
        - BACKUP_KEEP_DAYS=7
        - BACKUP_KEEP_WEEKS=4
        - BACKUP_KEEP_MONTHS=6
        - HEALTHCHECK_PORT=8080
    networks:
      - my_network

While service itself works fine and backups are created correctly when inspecting the docker container I see that it has 2 mounts created:

{
    "Type": "bind",
    "Source": "/opt/db_backups",
    "Destination": "/backups",
    "Mode": "rw",
    "RW": true,
    "Propagation": "rprivate"
},
{
    "Type": "volume",
    "Name": "1befc40bfde09598482a395405354b1dc1ff02973f4b600f4ea212ba7d568b33",
    "Source": "/var/lib/docker/volumes/1befc40bfde09598482a395405354b1dc1ff02973f4b600f4ea212ba7d568b33/_data",
    "Destination": "/var/lib/postgresql/data",
    "Driver": "local",
    "Mode": "",
    "RW": true,
    "Propagation": ""
}

While the first one is totally expected, the other one seems to be re-created on each container startup and remains empty. This inevitably results in trashing docker/volumes with many not needed and empty volumes.

Is that result of my setup or can it be improved in container itself?

Thanks for letting me know!

[krzychuz]

Okay, upon further investigation I realized that backup container actually specifies two anonymous volumes:

"Volumes": {
                "/backups": {},
                "/var/lib/postgresql/data": {}
            },

After adding this volume to docker compose as named volume it works as expected:

services:
  (...)
  postgresql_backup:
    (...)
    volumes:
        - /opt/db_backups/:/backups
        - backup-data:/var/lib/postgresql/data
     (...)
volumes:
  database-data:

Still I think the docker compose snipped in readme should be updated to avoid this by default 😉