How create mount point in docker-compose.yml

Question

I want create mount point for file path /my/host/dir. I create volumes in docker-compose.yml

volumes:
  data-db: /my/host/dir

and i try use db-data

postgres:
    image: postgres:14.2
    volumes:
      - db-data:/var/lib/postgresql/data

but i get ERROR: In file './docker-compose.yml', volume 'db-data' must be a mapping not a string.

My docker-compose.yml:

version: '3.9'
services:
  postgres:
    image: postgres:14.2
    volumes:
      - db-data:/var/lib/postgresql/data

volumes:
  db-data: /home/db/ 

Answer 1

version: '3.9'
services:
  postgres:
    image: postgres:14.2
    volumes:
      - db-data:/var/lib/postgresql/data

volumes:
  db-data: 

Notice the deleted path under the root volumes key. The root "volumes" only specifies that it exists, not the path where. For more info and list of available configuration options check the docs: https://docs.docker.com/compose/compose-file/compose-file-v3/#volume-configuration-reference

To elaborate more what the error means... You can specify the volume like this:

volumes:
  db-data:
    external: true
    name: my-db-data

So docker expects the "thing" following the : after db-data to be a key/value mapping. But you provided string /home/db instead.