self-hosting/modules/monit.nix

{
  config,
  lib,
  pkgs,
  ...
}:
with lib;
let
  cfg = config.custom.services.monit;
in
{
  options.custom.services.monit = {
    enable = mkEnableOption "monit";

    additionalConfig = mkOption {
      type = types.lines;
      default = "";
    };
  };

  config = lib.mkIf cfg.enable {

    sops.secrets = {
      monitMailserverConfig = {
        key = "monit/mailserver_config";
      };
    };

    services.monit = {
      enable = true;
      config = ''
        set daemon 30
          with start delay 90

        set httpd
          port 2812
          use address 127.0.0.1
          allow localhost

        set ssl {
          verify     : enable,
        }

        include ${config.sops.secrets.monitMailserverConfig.path}

        set mail-format { from: monit@banditlair.com }
        set alert alerts@banditlair.com with reminder on 120 cycles

        check program failed-units with path "${pkgs.systemd}/bin/systemctl --failed"
          if content != "0 loaded units listed" for 20 times within 60 cycles then alert

        check system $HOST
          if cpu usage > 95% for 10 cycles then alert
          if memory usage > 75% for 5 times within 15 cycles then alert
          if swap usage > 50% then alert

        check filesystem root with path /
          if SPACE usage > 90% then alert

        check file daily-backup-done with path /nix/var/data/backup/backup-ok
          if changed timestamp then alert
          if timestamp > 26 hours then alert

        ${cfg.additionalConfig}
      '';
    };
  };
}