DockBridge

Velocity plugin to auto-register Docker-backed servers (e.g., Limbo) and check for updates on Modrinth.

Features

• Auto-discovery: Containers with label net.uebliche.dockbridge.autoregister=true are registered as Velocity servers. Host from container name, port from label net.uebliche.dockbridge.server_port (fallback: first exposed port, else 25565).
• Name collisions: Default suffix → append short container id (basename-abcdef). Alternative overwrite → keep basename, last writer wins.
• /dockbridge command (permission dockbridge.command): Shows label filter, duplicate strategy, last scan stats, and registered servers (no sensitive data).
• Modrinth update check on proxy start; login hint for players with permission dockbridge.update.notify.

Installation

1. Download the latest DockBridge release from Modrinth (jar file).
2. Place the jar into your Velocity plugins/ folder.
3. (Optional) If Velocity runs in Docker, mount /var/run/docker.sock into the Velocity container so DockBridge can discover containers.
4. Start Velocity. On first start, the config file dockbridge.conf is created in the Velocity data folder; adjust settings and restart.
5. Permissions:
   • dockbridge.command for /dockbridge
   • dockbridge.update.notify for update hints on login

Configuration

dockbridge.conf (created in the Velocity data folder on first start):

docker.endpoint=unix:///var/run/docker.sock
docker.poll_interval_seconds=30
filters.proxy_group=default
docker.autoregister.label_key=net.uebliche.dockbridge.autoregister
docker.autoregister.label_value=true
docker.autoregister.name_label=net.uebliche.dockbridge.server_name
docker.autoregister.port_label=net.uebliche.dockbridge.server_port
docker.autoregister.duplicate_strategy=suffix   # suffix | overwrite

Docker labels (example)

net.uebliche.dockbridge.autoregister=true
net.uebliche.dockbridge.server_name=limbo
net.uebliche.dockbridge.server_port=30000

Local testing

Gradle run

./gradlew runVelocity

Downloads Velocity, builds the plugin (shadowJar), and starts the proxy with the plugin loaded.

Docker Compose (Limbo set)

docker compose up --build        # or: docker compose -f docker-compose.limbo.yml up --build

Includes three Limbo backends (ports 30000/30001/30002) and Velocity on host port 26678. Velocity runs via runVelocity inside the container and mounts your sources/config.

Commands & permissions

• /dockbridge (permission dockbridge.command): Status and registered servers.
• Update hint on login: permission dockbridge.update.notify.

Troubleshooting

• No servers registered?
  • Ensure your containers have the label net.uebliche.dockbridge.autoregister=true and a valid net.uebliche.dockbridge.server_port.
  • Make sure Velocity can reach Docker: mount /var/run/docker.sock (or set docker.endpoint to a reachable TCP endpoint).
  • Check /dockbridge output for last scan count and registered servers.
• Port mismatch or forwarding errors?
  • Verify the Limbo (or other backend) port matches the label and the server properties.
  • For Velocity forwarding, ensure forwarding secret/mode match on both ends.
• Duplicate names?
  • Default strategy is suffix. Switch to overwrite via docker.autoregister.duplicate_strategy if you want last-writer-wins.

Build

./gradlew build

Produces the shaded jar at build/libs/DockBridge-<version>.jar.

Contributing

• Fork & PRs welcome. Keep code comments minimal but purposeful.
• Default Java 21, Gradle Kotlin DSL, Velocity API 3.4.0-SNAPSHOT for run task; 3.1.1 for compileOnly/annotationProcessor.
• Run ./gradlew build before submitting; Docker-based tests are optional.