Notes

This is the most Important Thing to do in this Setup.



Utilizing systemd to create a Minecraft server that can start on demand and stop when it has no player

Written by Solene on 20 August 2022. Tags: #minecraft #nixos #systemd #automation





Introduction to SS

Sometimes it seems like I have specific needs I have to tackle on my own. Today, I wanted to set up a local Minecraft server running on my personal computer and only when someone needs it. Instead of running a massive Java server, a Minecraft server would be started when a user connects and would stop once no player remains.



However after looking deeper into the subject it appears that I'm not the only one who requires this.



on-demand Minecraft: a project to automatically start a remote cloud server for whitelisted players



minecraft-server-hibernation: a wrapper that starts and stop a Minecraft server upon condition



In general I don't want to rely on third party tools, so I found an alternative to do this by using systemd.



Even better, keep in mind that this technique can work with any daemon provided you are able to programmatically obtain the information about whether to allow it running or stop. I am using Minecraft in this instance. The server's stop is determined by the fetch performed by the player via the rcon (a remote administration protocol).





The setup SS

To illustrate the dependencies, I made an easy graph. There are a lot of systemd components that go into this.



The most important part of this setup is the usage of the systemd proxyifier. It's an application that accepts a connection via TCP, relays it to another socket, and then allows you to do other things like start a server and wait until it's fully operational. This is the key of this configuration, without it, this wouldn't be achieved.



Basically, listen-minecraft.socket listens on the public TCP port and runs listen-minecraft.service upon connection. This service needs hook-minecraft.service which is responsible for stopping or starting minecraft, but will also make listen-minecraft.service wait for the TCP port to be open so the proxifier will relay the connection to the daemon.



Then, minecraft-server.service is started alongside with stop-minecraft.timer which will regularly run stop-minecraft.service to try to stop the server if possible.
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Configuration for SS

I used NixOS to configure my on-demand Minecraft server. This can be done on any systemd-capable system. However I will provide an NixOS example so that you can easily convert it into regular systemd configuration files.





Conclusion The SS



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