mongodb: allow running as a replicaset member

also useful for point-in time backups using mongodump --oplog

svn path=/nixos/trunk/; revision=33509

modules/services/databases/mongodb.nix

@@ -17,6 +17,7 @@ let
     dbpath = ${cfg.dbpath}
     logpath = ${cfg.logpath}
     logappend = ${b2s cfg.logappend}
+    ${optionalString (cfg.replSetName != "") "replSet = ${cfg.replSetName}"}
   '';
 
 in
@@ -77,6 +78,14 @@ in
         default = false;
         description = "Use V8 instead of spidermonkey for js execution";
       };
+
+      replSetName = mkOption {
+        default = "";
+        description = ''
+          If this instance is part of a replica set, set its name here.
+          Otherwise, leave empty to run as single node.
+        '';
+      };
     };
 
   };