Docker for Mac and mkdir permisions

Question

Using the docker for mac app. Just installed everything yesterday. Finally got the app going. But I can't run migrations till I install postgis. So I dropped the official postgres dockerhub image for postgis:11-alpine image. But I keep on getting a permission denied issue when docker tries to mkdir for the pg_data volume.

Dockerfile:

        version: '3'

    # Containers we are going to run
    services:
      # Our Phoenix container
      phoenix:
        # The build parameters for this container.
        build:
          # Here we define that it should build from the current directory
          context: .
        environment:
          # Variables to connect to our Postgres server
          PGUSER: postgres
          PGPASSWORD: postgres
          PGDATABASE: gametime_dev
          PGPORT: 5432
          # Hostname of our Postgres container
          PGHOST: db
        ports:
          # Mapping the port to make the Phoenix app accessible outside of the container
          - "4000:4000"
        depends_on:
          # The db container needs to be started before we start this container
          - db
          - redis

      redis:
        image: "redis:alpine"
        ports:
          - "6379:6379"
        sysctls:
          net.core.somaxconn: 1024

      db:
        # We use the predefined Postgres image
        image: mdillon/postgis:11-alpine
        environment:
          # Set user/password for Postgres
          POSTGRES_USER: postgres
          POSTGRES_PASSWORD: postgres
          # Set a path where Postgres should store the data
          PGDATA: /var/lib/postgresql/data/pgdata
        restart: always
        volumes:
          - pgdata:/usr/local/var/postgres_data
    # Define the volumes
    volumes:
      pgdata:

Error I'm getting:

db_1       | mkdir: can't create directory '/var/lib/postgresql/data/pgdata': Permission denied

This does not happen though when using the postgres(official) image. I have googled high and low. I did read something about Docker for Mac running commands on the containers it creates in a VM as the current user's localhost user and not root. But that doesn't make sense to me - how do I get around this, if that's the case?

[Extra note:] - I did try the :z and :Z - still got the exact same error as above.

Appreciate the the time - in advance.

Answer 1

Your environment variables for the db service state that PGDATA is in /var/lib/postgresql/data/pgdata but you are mounting a pgdata volume in the container at /usr/local/var/postgres_data.

My guess is that when postgres starts, it is looking at the env vars and expecting a dir in /var/lib/postgresql/data/pgdata. Since it probably does not exists, it is trying to create it as postgres user which does not have the right to do it.

Use the same path for both vars and I'm quite sure it will fix the error.