DevShell — Ubuntu 24.04 Development Container for Synology NAS

A containerized Ubuntu 24.04 development environment running on a Synology NAS, accessible via VS Code Remote SSH from any machine.

Features

• Ubuntu 24.04 LTS base image
• SSH-only authentication (key-based, no passwords)
• Docker CLI + Compose v2 via host socket passthrough
• Full /volume1 access — NAS files accessible at the same path inside the container, so docker compose file references resolve correctly
• Persistent VS Code Server — named volume survives container restarts (no re-download on reconnect)
• User identity mirroring — UID/GID matches Synology user account
• GitHub Actions CI/CD — image built externally to avoid DS220+ CPU load, pushed to GHCR

Architecture

VS Code (Windows)
  └─ SSH ProxyCommand
       └─ ssh synology (port 54321)
            └─ docker exec devshell nc localhost 22
                 └─ devshell container (Ubuntu 24.04)
                      ├─ /var/run/docker.sock → host Docker
                      └─ /volume1 → NAS storage

Traffic flow for web services:

Internet → Cloudflare Tunnel → cloudflared container → Traefik (:8080) → services

Prerequisites

On Synology NAS

# Get Docker socket GID
stat -c %g /var/run/docker.sock

# Create stack directory and SSH keys directory
mkdir -p /volume1/docker/stacks/devshell/ssh

# Add your public SSH key
cat ~/.ssh/id_ed25519.pub >> /volume1/docker/stacks/devshell/ssh/authorized_keys
chmod 600 /volume1/docker/stacks/devshell/ssh/authorized_keys

Deployment

1. Clone / copy files to NAS

mkdir -p /volume1/docker/stacks/devshell
cd /volume1/docker/stacks/devshell
# Copy docker-compose.yml here

2. Create .env

cp .env.example .env
nano .env

GITHUB_USERNAME=vidalstephen
USERNAME=msn0624c
USER_UID=1026
USER_GID=100
ADMIN_GID=101
DOCKER_GID=968        # use value from: stat -c %g /var/run/docker.sock
DOCKER_API_VERSION=1.43

3. Deploy

cd /volume1/docker/stacks/devshell
/usr/local/bin/docker compose pull
/usr/local/bin/docker compose up -d

VS Code Remote SSH Setup

~/.ssh/config

Host synology
  HostName ngaged.synology.me
  User msn0624c
  Port 54321
  IdentityFile ~/.ssh/id_ed25519

Host devshell
  HostName localhost
  Port 22
  User msn0624c
  IdentityFile ~/.ssh/id_ed25519
  ProxyCommand ssh -p 54321 msn0624c@ngaged.synology.me "/usr/local/bin/docker exec -i devshell nc localhost 22"

VS Code Settings

Add to settings.json (required — devshell downloads the server binary directly from Microsoft's CDN):

"remote.SSH.localServerDownload": "off"

Connect

In VS Code: Remote Explorer → SSH → devshell

First connection downloads the VS Code Server (~112MB) into the persistent devshell-vscode-server volume. Subsequent connections are instant.

Updating

cd /volume1/docker/stacks/devshell
/usr/local/bin/docker compose pull
/usr/local/bin/docker compose up -d

Troubleshooting

# Container logs
/usr/local/bin/docker compose logs devshell

# Verify Docker socket access from inside container
/usr/local/bin/docker exec devshell docker ps

# Check SSH keys are mounted
/usr/local/bin/docker exec devshell ls -la /home/msn0624c/.ssh/

# Check user identity
/usr/local/bin/docker exec devshell id msn0624c

VS Code Server download fails

If VS Code shows ServerDownloadFailed:

• Confirm "remote.SSH.localServerDownload": "off" is set in VS Code settings
• Test CDN access: docker exec devshell curl -sI https://update.code.visualstudio.com
• Check .vscode-server ownership: docker exec devshell ls -la ~ — must be owned by msn0624c, not root

Security Notes

• SSH key authentication only — password auth disabled
• Root SSH login disabled
• Port 2222 is bound to 127.0.0.1 only — not directly reachable from outside the NAS
• Docker socket access is intentional for this dev environment
• DOCKER_API_VERSION is set to match the Synology Docker daemon version

Directory Structure

devshell/
├── .github/workflows/build-and-push.yml   # CI/CD
├── Dockerfile                              # Container image
├── entrypoint.sh                           # Runtime setup (users, perms, sshd)
├── docker-compose.yml                      # Stack definition
├── .env.example                            # Environment variable template
└── README.md

# On NAS:
/volume1/docker/stacks/devshell/
├── docker-compose.yml
├── .env                                    # Credentials — never commit
└── ssh/
    └── authorized_keys                     # SSH public keys