Trouble with Docker Host Mounts from /home/user in Firebase Studio (IDX) - Permission Issues?

General
1

Hi everyone,

I’m working with Docker and Docker Compose within my Firebase Studio (IDX) workspace. My environment is configured using .idx/dev.nix with services.docker.enable = true; and I’m using docker-compose to manage services like databases.

The Problem:

I’m encountering issues when I try to use host volume mounts to map directories or files from my workspace’s home directory (e.g., /home/user/my-project-data/) directly into a running container.

For example, in my docker-compose.yml:

# docker-compose.yml (Example with Host Mount)
services:
  my-database:
    image: some-database-image:latest
    volumes:
      # Attempting to mount data from the IDX workspace user's home
      - /home/user/my-database-files/data:/var/lib/database/data
      - /home/user/my-database-files/config:/etc/database/config
    # ... other service config

When I try to run this configuration, the my-database container often fails to start correctly. Checking the container logs (docker logs <container_id>) frequently reveals errors like:

  • Permission denied when trying to read/write files in the mounted directories (e.g., /var/lib/database/data).
  • Errors related to creating lock files.
  • Sometimes, the container just exits silently with a non-zero exit code shortly after starting.

My Understanding (The Suspected Cause):

My guess is that this is a user/permission mismatch issue inherent in how Docker runs within the IDX environment:

  1. The files and directories under /home/user/ in the workspace belong to the default workspace user (let’s call it user, with a specific UID/GID).
  2. The process inside the Docker container (e.g., the database server) often runs as a different user (e.g., postgres, mysql, firebird, or sometimes root, but still with a potentially different UID/GID context than the host user).
  3. This container user does not have the necessary file system permissions to read, write, or modify files owned by the workspace user in the host-mounted volume.

Interestingly, this kind of direct host mount might sometimes appear to work on a local machine (especially with Docker Desktop on Windows/macOS, which can handle some permission mapping), but it seems to consistently fail in the standard Linux environment provided by Firebase Studio (IDX).

Proposed Solution: Named Volumes

Based on Docker best practices, it seems the correct approach for managing persistent data or configuration within containers in this environment is to use named Docker volumes:

# docker-compose.yml (Example with Named Volumes)
services:
  my-database:
    image: some-database-image:latest
    volumes:
      # Use named volumes instead of host paths
      - db-data:/var/lib/database/data
      - db-config:/etc/database/config
    # ... other service config

# Declare the named volumes at the top level
volumes:
  db-data:
  db-config:

My understanding is that Docker manages the storage location and permissions for these named volumes itself, ensuring that the container process has the appropriate access rights. If I need to initialize these volumes with existing data from my workspace, I would likely need a separate step (e.g., an entrypoint script in my image or a one-off command) to copy the data from /home/user/... into the volume the first time the container is created.

My Question:

Could someone please confirm if my understanding of this permission issue with host mounts from /home/user/ in Firebase Studio (IDX) is correct?

Is using named Docker volumes the standard and recommended practice for managing data persistence for services running via Docker Compose within IDX?

Thanks in advance for any clarification or guidance!