nixos-config/modules/nixos/services/gameserver/minecraft-server.nix

{ inputs, config, pkgs, lib, ... }:


{
  networking.firewall = {
    allowedTCPPorts = [ 10000 ];
    allowedUDPPorts = [ 10000 ];
  };

  users = {
    users.minecraft = {
      group = "minecraft";
      isSystemUser = true;

      home = "/var/lib/minecraft";
      createHome = true;
    };
    groups.minecraft = {};
  };

  environment.systemPackages =
  let
    nixpkgs-unstable = import inputs.nixpkgs-unstable {
      system = "${pkgs.system}";
      config.allowUnfree = true;
    };
  in [
    # to control the interactive server console
    pkgs.screen

    nixpkgs-unstable.graalvmPackages.graalvm-oracle_17
    inputs.nixpkgs-pin.legacyPackages.${pkgs.system}.graalvm-ce
  ];

  environment.etc = {
    "minecraft/java21_args".text = ''
      -Xmx8G
      -Xms8G
      --add-modules=jdk.incubator.vector
      -XX:+UseG1GC
      -XX:MaxGCPauseMillis=200
      -XX:+UnlockExperimentalVMOptions
      -XX:+UnlockDiagnosticVMOptions
      -XX:+DisableExplicitGC
      -XX:+AlwaysPreTouch
      -XX:G1NewSizePercent=28
      -XX:G1MaxNewSizePercent=50
      -XX:G1HeapRegionSize=16M
      -XX:G1ReservePercent=15
      -XX:G1MixedGCCountTarget=3
      -XX:InitiatingHeapOccupancyPercent=20
      -XX:G1MixedGCLiveThresholdPercent=90
      -XX:SurvivorRatio=32
      -XX:G1HeapWastePercent=5
      -XX:MaxTenuringThreshold=1
      -XX:+PerfDisableSharedMem
      -XX:G1SATBBufferEnqueueingThresholdPercent=30
      -XX:G1ConcMarkStepDurationMillis=5
      -XX:G1RSetUpdatingPauseTimePercent=0
      -XX:+UseNUMA
      -XX:-DontCompileHugeMethods
      -XX:MaxNodeLimit=240000
      -XX:NodeLimitFudgeFactor=8000
      -XX:ReservedCodeCacheSize=400M
      -XX:NonNMethodCodeHeapSize=12M
      -XX:ProfiledCodeHeapSize=194M
      -XX:NonProfiledCodeHeapSize=194M
      -XX:NmethodSweepActivity=1
      -XX:+UseFastUnorderedTimeStamps
      -XX:+UseCriticalJavaThreadPriority
      -XX:AllocatePrefetchStyle=3
      -XX:+AlwaysActAsServerClassMachine
      -XX:+UseTransparentHugePages
      -XX:LargePageSizeInBytes=2M
      -XX:+UseLargePages
      -XX:+EagerJVMCI
      -XX:+UseStringDeduplication
      -XX:+UseAES
      -XX:+UseAESIntrinsics
      -XX:+UseFMA
      -XX:+UseLoopPredicate
      -XX:+RangeCheckElimination
      -XX:+OptimizeStringConcat
      -XX:+UseCompressedOops
      -XX:+UseThreadPriorities
      -XX:+OmitStackTraceInFastThrow
      -XX:+RewriteBytecodes
      -XX:+RewriteFrequentPairs
      -XX:+UseFPUForSpilling
      -XX:+UseFastStosb
      -XX:+UseNewLongLShift
      -XX:+UseVectorCmov
      -XX:+UseXMMForArrayCopy
      -XX:+UseXmmI2D
      -XX:+UseXmmI2F
      -XX:+UseXmmLoadAndClearUpper
      -XX:+UseXmmRegToRegMoveAll
      -XX:+EliminateLocks
      -XX:+DoEscapeAnalysis
      -XX:+AlignVector
      -XX:+OptimizeFill
      -XX:+EnableVectorSupport
      -XX:+UseCharacterCompareIntrinsics
      -XX:+UseCopySignIntrinsic
      -XX:+UseVectorStubs
      -XX:UseAVX=2
      -XX:UseSSE=4
      -XX:+UseFastJNIAccessors
      -XX:+UseInlineCaches
      -XX:+SegmentedCodeCache
      -Djdk.nio.maxCachedBufferSize=262144
      -Djdk.graal.UsePriorityInlining=true
      -Djdk.graal.Vectorization=true
      -Djdk.graal.OptDuplication=true
      -Djdk.graal.DetectInvertedLoopsAsCounted=true
      -Djdk.graal.LoopInversion=true
      -Djdk.graal.VectorizeHashes=true
      -Djdk.graal.EnterprisePartialUnroll=true
      -Djdk.graal.VectorizeSIMD=true
      -Djdk.graal.StripMineNonCountedLoops=true
      -Djdk.graal.SpeculativeGuardMovement=true
      -Djdk.graal.TuneInlinerExploration=1
      -Djdk.graal.LoopRotation=true
      -Djdk.graal.CompilerConfiguration=enterprise
    '';
  };

  systemd.services.minecraft = {
    description = "Minecraft Java Edition server";
    wants = [ "network-online.target" ];
    after = [ "network-online.target" ];

    path = [ pkgs.screen ];
    script = "screen -dmS minecraft -- ${lib.getExe inputs.nixpkgs-pin.legacyPackages.${pkgs.system}.graalvm-ce} @/etc/minecraft/java21_args -jar server.jar nogui";

    serviceConfig = {
      User = "minecraft";
      Group = "minecraft";
      WorkingDirectory = "/var/lib/minecraft/vanilla";
      Type = "forking";
      Restart = "on-failure";
      TimerSlackNSec = "5ms";

      # very necessary and sane hardening for a private minecraft server
      CapabilityBoundingSet = [ "" ];
      DeviceAllow = [ "" ];
      DevicePolicy = "strict";
      LockPersonality = true;
      MemoryDenyWriteExecute = true;
      NoNewPrivileges = true;
      PrivateDevices = true;
      PrivateTmp = true;
      PrivateUsers = true;
      ProcSubset = "pid";
      ProtectClock = true;
      ProtectControlGroups = true;
      ProtectHome = true;
      ProtectHostname = true;
      ProtectKernelLogs = true;
      ProtectKernelModules = true;
      ProtectKernelTunables = true;
      ProtectProc = "invisible";
      ProtectSystem = "strict";
      RemoveIPC = true;
      RestrictAddressFamilies = [
        "AF_INET"
        "AF_INET6"
        "AF_UNIX"
      ];
      RestrictNamespaces = true;
      RestrictRealtime = true;
      RestrictSUIDSGID = true;
      SystemCallArchitectures = "native";
      SystemCallFilter = [ "@system-service" ];
      UMask = "0027";
    };
  };
}