nixos/mesos: Parameterize mesos slave attributes

Added attributes to nixos/tests/mesos.nix to verify that mesos-slave
attributes work. If the generated attributes are invalid, the daemon
should fail to start.

Change-Id: I5511245add30aba658b1af22cd7355b0bbf5d15c

nixos/modules/services/misc/mesos-slave.nix

@@ -5,6 +5,13 @@ with lib;
 let
   cfg = config.services.mesos.slave;
 
+  mkAttributes =
+    attrs: concatStringsSep ";" (mapAttrsToList
+                                   (k: v: "${k}:${v}")
+                                   (filterAttrs (k: v: v != null) attrs));
+  attribsArg = optionalString (cfg.attributes != {})
+                              "--attributes=${mkAttributes cfg.attributes}";
+
 in {
 
   options.services.mesos = {
@@ -62,6 +69,19 @@ in {
         type = types.str;
       };
 
+      attributes = mkOption {
+        description = ''
+          Machine attributes for the slave instance.
+
+          Use caution when changing this; you may need to manually reset slave
+          metadata before the slave can re-register.
+        '';
+        default = {};
+        type = types.attrsOf types.str;
+        example = { rack = "aa";
+                    host = "aabc123";
+                    os = "nixos"; };
+      };
     };
 
   };
@@ -79,6 +99,7 @@ in {
             --port=${toString cfg.port} \
             --master=${cfg.master} \
             ${optionalString cfg.withHadoop "--hadoop-home=${pkgs.hadoop}"} \
+            ${attribsArg} \
             --work_dir=${cfg.workDir} \
             --logging_level=${cfg.logLevel} \
             --docker=${pkgs.docker}/libexec/docker/docker \

nixos/tests/mesos.nix

@@ -8,6 +8,10 @@ import ./make-test.nix {
       slave = {
         enable = true;
         master = "zk://localhost:2181/mesos";
+        attributes = {
+          tag1 = "foo";
+          tag2 = "bar";
+        };
       };
       master = {
         enable = true;