# Configuration from https://dataswamp.org/~solene/2022-08-20-on-demand-minecraft-with-systemd.html { config, lib, pkgs, modulesPath, ... }: let # check every 20 seconds if the server # need to be stopped frequency-check-players = "*-*-* *:*:0/20"; # time in second before we could stop the server # this should let it time to spawn minimum-server-lifetime = 300; # minecraft port # used in a few places in the code # this is not the port that should be used publicly # don't need to open it on the firewall minecraft-port = 25564; # this is the port that will trigger the server start # and the one that should be used by players # you need to open it in the firewall public-port = 25565; # a rcon password used by the local systemd commands # to get information about the server such as the # player list # this will be stored plaintext in the store rcon-password = "260a368f55f4fb4fa"; # a script used by hook-minecraft.service # to start minecraft and the timer regularly # polling for stopping it start-mc = pkgs.writeShellScriptBin "start-mc" '' systemctl start minecraft-server.service systemctl start stop-minecraft.timer ''; # wait 60s for a TCP socket to be available # to wait in the proxifier # idea found in https://blog.developer.atlassian.com/docker-systemd-socket-activation/ wait-tcp = pkgs.writeShellScriptBin "wait-tcp" '' for i in `seq 60`; do if ${pkgs.libressl.nc}/bin/nc -z 127.0.0.1 ${toString minecraft-port} > /dev/null ; then exit 0 fi ${pkgs.busybox.out}/bin/sleep 1 done exit 1 ''; # script returning true if the server has to be shutdown # for minecraft, uses rcon to get the player list # skips the checks if the service started less than minimum-server-lifetime no-player-connected = pkgs.writeShellScriptBin "no-player-connected" '' servicestartsec=$(date -d "$(systemctl show --property=ActiveEnterTimestamp minecraft-server.service | cut -d= -f2)" +%s) serviceelapsedsec=$(( $(date +%s) - servicestartsec)) # exit if the server started less than 5 minutes ago if [ $serviceelapsedsec -lt ${toString minimum-server-lifetime} ] then echo "server is too young to be stopped" exit 1 fi PLAYERS=`printf "list\n" | ${pkgs.rcon.out}/bin/rcon -m -H 127.0.0.1 -p 25575 -P ${rcon-password}` if echo "$PLAYERS" | grep "are 0 of a" then exit 0 else exit 1 fi ''; in { networking.firewall = { allowedTCPPorts = [public-port]; allowedUDPPorts = [public-port]; }; # use NixOS module to declare your Minecraft # rcon is mandatory for no-player-connected services.minecraft-server = { enable = true; eula = true; openFirewall = false; declarative = true; whitelist = { "Tux922" = "b1848d60-4ddd-4fa4-a328-fb269910b6ae"; }; serverProperties = { server-port = minecraft-port; difficulty = 3; gamemode = "survival"; force-gamemode = true; max-players = 10; # level-seed = 238902389203; motd = "NixOS Minecraft server!"; white-list = true; enable-rcon = true; "rcon.password" = rcon-password; }; }; # don't start Minecraft on startup systemd.services.minecraft-server = { wantedBy = pkgs.lib.mkForce []; }; # this waits for incoming connection on public-port # and triggers listen-minecraft.service upon connection systemd.sockets.listen-minecraft = { enable = true; wantedBy = ["sockets.target"]; requires = ["network.target"]; listenStreams = ["${toString public-port}"]; }; # this is triggered by a connection on TCP port public-port # start hook-minecraft if not running yet and wait for it to return # then, proxify the TCP connection to the real Minecraft port on localhost systemd.services.listen-minecraft = { path = with pkgs; [systemd]; enable = true; requires = ["hook-minecraft.service" "listen-minecraft.socket"]; after = ["hook-minecraft.service" "listen-minecraft.socket"]; serviceConfig.ExecStart = "${pkgs.systemd.out}/lib/systemd/systemd-socket-proxyd 127.0.0.1:${toString minecraft-port}"; }; # this starts Minecraft is required # and wait for it to be available over TCP # to unlock listen-minecraft.service proxy systemd.services.hook-minecraft = { path = with pkgs; [systemd libressl busybox]; enable = true; serviceConfig = { ExecStartPost = "${wait-tcp.out}/bin/wait-tcp"; ExecStart = "${start-mc.out}/bin/start-mc"; }; }; # create a timer running every frequency-check-players # that runs stop-minecraft.service script on a regular # basis to check if the server needs to be stopped systemd.timers.stop-minecraft = { enable = true; timerConfig = { OnCalendar = "${frequency-check-players}"; Unit = "stop-minecraft.service"; }; wantedBy = ["timers.target"]; }; # run the script no-player-connected # and if it returns true, stop the minecraft-server # but also the timer and the hook-minecraft service # to prepare a working state ready to resume the # server again systemd.services.stop-minecraft = { enable = true; serviceConfig.Type = "oneshot"; script = '' if ${no-player-connected}/bin/no-player-connected then echo "stopping server" systemctl stop minecraft-server.service systemctl stop hook-minecraft.service systemctl stop stop-minecraft.timer fi ''; }; }