It looks like there are some problems with the volume configuration in your Grafana container:

First, I think this was simply a typo in your question:

      - grafana_ini:/etc/grafana/grafana.inianticipated location in container

I suspect that you were actually intending this:

      - grafana_ini:/etc/grafana/grafana.ini

Which doesn't make any sense: grafana.ini is a file, but a volume is a directory. Docker won't allow you to mount a directory on top of a file, hence the error:

ERROR: .../etc/grafana/grafana.ini is not directory

You have the same problem with the grafana_data volume, which you're attempting to mount on top of datasource.yml:

      - grafana_data:/etc/grafana/provisioning/datasources/datasource.yml

I think you may be approaching this configuration in the wrong way; you may want to read through these documents:

• https://grafana.com/docs/grafana/latest/installation/docker/
• https://grafana.com/docs/grafana/latest/administration/configure-docker/
• https://grafana.com/docs/grafana/latest/administration/provisioning/

It is possible to configure Grafana (and Prometheus!) using only bind mounts and environment variables (this includes installing plugin, data sources, and dashboards), so you don't need to build your own custom images.

Unrelated to this particular problem, there are some other things in your docker-compose.yml that are worth changing. You should no longer be using the links directive...

    links:
      - prometheus

...because Docker maintains DNS for you automatically; your containers can refer to each other by name with no additional configuration.

Docker provides for volumes as the way to persist volumes between container invocations and to share data between containers.

They are quite simple to declare and use in compose files:

volumes:
  postgres:
  grafana:

services:
  db:
    image: postgres
    ports:
      - "5432:5432"
    environment:
      - POSTGRES_PASSWORD=my_secret_password
    volumes:
      - postgres:/var/lib/postgresql/data
      
  grafana:
    image: grafana/grafana
    depends_on:
      - db
    volumes:
      - grafana:/var/lib/grafana
    ports:
      - "3000:3000"

Optionally, you can also set a local directory as your container volume with the added convince of having the files easily accessible not only from inside the container. This is especially helpful for mounting specific config files to their location in the container, you can edit the file locally like any other file restart the container with the updated configuration (certificates and other similar files also make good use of this option). And you do that like so:

    volumes:
     - /home/myusername/postgres_data/:/var/lib/postgresql/data/

PS. I have omitted the container_name and version directives from this compose.yml because (as of docker 20.10), the docker compose spec determines version automatically, and docker compose exposes enough functionality that accessing the containers directly using short names isn't necessary usually.

The data is not stored in /usr/src/grafana but in /var/lib/grafana. In consequence, your volume-definition in docker-compose.yml is wrong and everytime the container is recreated, the data is lost.

Change the path to /var/lib/grafana and it should work:

services:
  grafana:
    [...]
    volumes:
      - "grafana-storage:/var/lib/grafana"