!AutoStopper - Empty servers sleep. Players wake them.

Stop running empty Minecraft servers

Your players should not have to care whether a backend server is running, and you should not have to keep every server online when nobody is using it.

AutoStopper gives a Velocity network both. It stops mapped Docker-based backend servers after they have been empty for a while, then starts them automatically the next time a player connects. Players use your network normally; AutoStopper handles the container lifecycle and waits until the server is genuinely ready before sending them through.

Install it on Velocity, map the containers you want it to manage, and let quiet servers sleep.

Why use AutoStopper?

Save resources when your network is quiet

AutoStopper watches only the servers you explicitly map. Once a monitored server has no connected players and passes its inactivity timeout, its container is stopped. Always-on hubs and lobbies can remain completely unmonitored.

Wake servers when players need them

When a player connects to a sleeping backend, AutoStopper starts the mapped container and keeps the request moving. Players do not need a client mod, a special account, or a replacement /server command.

Wait for Minecraft, not just a running container

Running=true does not mean a Minecraft server is ready. AutoStopper can wait for a valid Minecraft status response, Docker health, or either signal before connecting the player. Every probe and Docker command has a bounded deadline.

Handle the rush back in

If several players arrive at once, they share one startup and readiness operation instead of racing multiple container starts. Waiting players are connected when the backend becomes ready.

Fail clearly and recover safely

Failed automatic stops use capped retries without pretending the server stopped. Atomic reloads keep the previous configuration active if the replacement is invalid. /autostopper status shows safe operational details and a suggested action while raw Docker output stays in operator logs.

What the player experiences

1. The player selects a monitored server through normal Velocity routing.
2. If its container is stopped, AutoStopper tells the player it is waking the server.
3. AutoStopper starts one shared lifecycle operation and waits for real readiness.
4. The player is connected as soon as the backend can answer Minecraft traffic.
5. After everyone leaves and the inactivity period expires, the container sleeps again.

If the backend is already available, the connection proceeds normally. Servers omitted from monitored_servers are never intercepted, started, or stopped by AutoStopper.

Tested support

One Java 21 bytecode AutoStopper JAR is tested on all three complete runtime lines below:

Support line	Role	Proxy image	Java	Velocity
Legacy	Minimum/floor	itzg/mc-proxy:2026.8.0-java21	21	3.5.1 build 615
Stable	Production	itzg/mc-proxy:2026.8.0-java25	25	4.0.0 build 6
Preview	Snapshot validation	itzg/mc-proxy:2026.8.0-java25	25	4.1.0-SNAPSHOT build 16

Velocity 4.x requires at least Java 25; the preview line validates a PaperMC snapshot and is not a production baseline. Keep the proxy image/JVM and Velocity build from one row together. The real release-candidate stack is exercised with a Purpur 1.21.4 backend, actual protocol clients, simultaneous joins, idle stop, restart, never-ready behavior, and failed-stop retry on the stable line.

Quick start

1. Choose the complete Java 21 / Velocity 3.5.1 example (minimum), Java 25 / Velocity 4.0 example (recommended production), or Java 25 / Velocity 4.1 preview example.
2. Put the downloaded, unchanged JAR at velocity_server/plugins/AutoStopper.jar.
3. Register each managed backend in Velocity's [servers] table.
4. Start the stack once and edit the generated lowercase path velocity_server/plugins/autostopper/config.yml.
5. Map only real Velocity server names to existing Docker containers, then restart Velocity or run /autostopper reload.
6. Run /autostopper status and resolve any degraded mapping before opening the proxy to players.

Important Docker security warning: the tested installation mounts /var/run/docker.sock into Velocity. Access to that socket is effectively equivalent to root control of the Docker host. Adding the proxy user to the socket group is not ordinary non-root isolation. Prefer a dedicated host or VM, install only trusted plugins, and read the full security guidance before starting the stack.

Managed backend containers must already exist and use restart: "no", otherwise Docker may undo a successful inactivity stop. Leave always-on hubs out of monitored_servers.

Sensible defaults, explicit control

• 5-minute inactivity timeout
• 10-second plugin shutdown deadline
• 3 automatic stop attempts with 60-to-300-second capped backoff
• Minecraft status readiness with a 120-second overall deadline
• no monitored containers until you explicitly add mappings

Every value is configurable, validated as one atomic snapshot, and documented in the configuration reference.

Commands and permissions

Command	Permission
/autostopper or /as	Public plugin information
/autostopper help	Public, permission-filtered help
/autostopper status	autostopper.command.status or autostopper.admin
/autostopper reload	autostopper.command.reload or autostopper.admin

AutoStopper does not register or replace Velocity's /server command and exposes no manual start or stop command.

Learn more

• Complete installation guide
• Configuration reference
• Troubleshooting
• 1.1.2 to 2.0.0 migration
• Changelog
• Report an issue

Ready to let empty servers sleep? Choose a pinned example, review the Docker security boundary, and install the same validated JAR published here and on GitHub Releases.