nixos/docker: add auto prune randomizedDelaySec and persistent options (#301547)

docker: add auto prune randomizedDelaySec and persistent options

Options mirror nix garbage collection

nixos/modules/virtualisation/docker.nix

@@ -159,6 +159,34 @@ in
           which the prune will occur.
         '';
       };
+
+      randomizedDelaySec = mkOption {
+        default = "0";
+        type = types.singleLineStr;
+        example = "45min";
+        description = ''
+          Add a randomized delay before each auto prune.
+          The delay will be chosen between zero and this value.
+          This value must be a time span in the format specified by
+          {manpage}`systemd.time(7)`
+        '';
+      };
+
+      persistent = mkOption {
+        default = true;
+        type = types.bool;
+        example = false;
+        description = ''
+          Takes a boolean argument. If true, the time when the service
+          unit was last triggered is stored on disk. When the timer is
+          activated, the service unit is triggered immediately if it
+          would have been triggered at least once during the time when
+          the timer was inactive. Such triggering is nonetheless
+          subject to the delay imposed by RandomizedDelaySec=. This is
+          useful to catch up on missed runs of the service when the
+          system was powered down.
+        '';
+      };
     };
 
     package = mkPackageOption pkgs "docker" { };
@@ -254,6 +282,13 @@ in
         requires = [ "docker.service" ];
       };
 
+      systemd.timers.docker-prune = mkIf cfg.autoPrune.enable {
+        timerConfig = {
+          RandomizedDelaySec = cfg.autoPrune.randomizedDelaySec;
+          Persistent = cfg.autoPrune.persistent;
+        };
+      };
+
       assertions = [
         { assertion = cfg.enableNvidia && pkgs.stdenv.hostPlatform.isx86_64 -> config.hardware.graphics.enable32Bit or false;
           message = "Option enableNvidia on x86_64 requires 32-bit support libraries";