feat(sterni/machines/ingeborg): regularly back up minecraft worlds r/7263

This is just intended as a local backup in case things go wrong
horribly, so you can revert to a recent state.

Change-Id: I1d666bad77045a1c807204df144422ba69d1d99f
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10417
Autosubmit: sterni <sternenseemann@systemli.org>
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI

2 files changed, 131 insertions, 2 deletions

diff --git a/users/sterni/machines/ingeborg/minecraft.nix b/users/sterni/machines/ingeborg/minecraft.nix
index ae367c5988..df6c531deb 100644
--- a/users/sterni/machines/ingeborg/minecraft.nix
+++ b/users/sterni/machines/ingeborg/minecraft.nix
@@ -38,11 +38,10 @@ let
   };
 in
 
-# TODO(sterni): regular backups of carpet world
-
 {
   imports = [
     ../../modules/minecraft-fabric.nix
+    ../../modules/backup-minecraft-fabric.nix
   ];
 
   config = {
@@ -65,6 +64,11 @@ in
       minecraft-rcon.file = depot.users.sterni.secrets."minecraft-rcon.age";
     };
 
+    services.backup-minecraft-fabric-servers = {
+      enable = true;
+      repository = "/srv/backup/from-local/minecraft";
+    };
+
     services.minecraft-fabric-server = {
       creative = {
         enable = false; # not actively used
diff --git a/users/sterni/modules/backup-minecraft-fabric.nix b/users/sterni/modules/backup-minecraft-fabric.nix
new file mode 100644
index 0000000000..a80a7f51a9
--- /dev/null
+++ b/users/sterni/modules/backup-minecraft-fabric.nix
@@ -0,0 +1,125 @@
+# Companion module to minecraft-fabric.nix which automatically and regularly
+# creates backups of all minecraft servers' worlds to a shared borg(1)
+# repository.
+#
+# SPDX-License-Identifier: MIT
+# SPDX-FileCopyrightText: 2023 sterni <sternenseemann@systemli.org>
+{ pkgs, depot, config, lib, ... }:
+
+let
+  inherit (depot.nix) getBins;
+
+  bins = getBins pkgs.borgbackup [ "borg" ]
+    // getBins pkgs.mcrcon [ "mcrcon" ];
+
+  unvaried = ls: builtins.all (l: l == builtins.head ls) ls;
+
+  cfg = config.services.backup-minecraft-fabric-servers;
+
+  instances = lib.filterAttrs (_: i: i.enable) config.services.minecraft-fabric-server;
+  users = lib.mapAttrsToList (_: i: i.user) instances;
+  groups = lib.mapAttrsToList (_: i: i.group) instances;
+
+  mkBackupScript = instanceName: instanceCfg:
+    let
+      archivePrefix = "minecraft-fabric-${instanceName}-world-${builtins.baseNameOf instanceCfg.world}-";
+    in
+
+    pkgs.writeShellScript "backup-minecraft-fabric-${instanceName}" ''
+      export MCRCON_HOST="localhost"
+      export MCRCON_PORT="${toString instanceCfg.serverProperties."rcon.port"}"
+      # Unfortunately, mcrcon can't read the password from a file
+      export MCRCON_PASS="$(cat "''${CREDENTIALS_DIRECTORY}/${instanceName}-rcon-password")"
+
+      ${bins.mcrcon} save-all
+      unset MCRCON_PASS
+
+      # Give the server plenty of time to save
+      sleep 60
+
+      ${bins.borg} ${lib.escapeShellArgs [
+        "create"
+        "--verbose" "--filter" "AMEU" "--list"
+        "--stats" "--show-rc"
+        "--compression" "zlib"
+        "${cfg.repository}::${archivePrefix}{now}"
+        instanceCfg.world
+      ]}
+
+      ${bins.borg} ${lib.escapeShellArgs [
+        "prune"
+        "--list"
+        "--show-rc"
+        "--glob-archives" "${archivePrefix}*"
+        "--keep-hourly" "168"
+        "--keep-daily" "31"
+        "--keep-monthly" "6"
+        "--keep-yearly" "2"
+        cfg.repository
+      ]}
+
+      ${bins.borg} compact ${lib.escapeShellArg cfg.repository}
+    '';
+in
+
+{
+  imports = [
+    ./minecraft-fabric.nix
+  ];
+
+  options = {
+    services.backup-minecraft-fabric-servers = {
+      enable = lib.mkEnableOption "backups of all Minecraft fabric servers";
+
+      repository = lib.mkOption {
+        type = lib.types.path;
+        description = "Path to the borg(1) repository to use for all backups.";
+        default = "/var/lib/backup/minecraft-fabric";
+      };
+    };
+  };
+
+  config = lib.mkIf (cfg.enable && builtins.length (builtins.attrNames instances) > 0) {
+    assertions = [
+      {
+        assertion = unvaried users && unvaried groups;
+        message = "all instances under services.minecraft-fabric-server must use the same user and group";
+      }
+    ];
+
+    environment.systemPackages = [
+      pkgs.borgbackup
+    ];
+
+    systemd = {
+      services.backup-minecraft-fabric-servers = {
+        description = "Backup world of all fabric based Minecraft servers";
+        wantedBy = [ ];
+        after = builtins.map
+          (name: "minecraft-fabric-${name}.service")
+          (builtins.attrNames instances);
+
+        script = lib.concatStrings (lib.mapAttrsToList mkBackupScript instances);
+
+        serviceConfig = {
+          Type = "oneshot";
+          User = builtins.head users;
+          Group = builtins.head groups;
+          LoadCredential = lib.mapAttrsToList
+            (instanceName: instanceCfg: "${instanceName}-rcon-password:${instanceCfg.rconPasswordFile}")
+            instances;
+        };
+      };
+
+      timers.backup-minecraft-fabric-servers = {
+        description = "Regularly backup Minecraft fabric servers";
+        wantedBy = [ "timers.target" ];
+        timerConfig = {
+          OnCalendar = "*-*-* 00/3:00:00";
+          Persistent = true;
+          RandomizedDelaySec = "1h";
+        };
+      };
+    };
+  };
+}