Milo: Add ts_mon metrics for master json datastore success

milo/appengine/buildbot/pubsub.go

Index: milo/appengine/buildbot/pubsub.go
diff --git a/milo/appengine/buildbot/pubsub.go b/milo/appengine/buildbot/pubsub.go
index 81dd9bfbc5c2b51510ef89f411fedaf17b2a2868..66ecd8caf78f956351854cd0fd9ca93016723538 100644
--- a/milo/appengine/buildbot/pubsub.go
+++ b/milo/appengine/buildbot/pubsub.go
@@ -42,6 +42,15 @@ var (
 		field.Bool("finished"),
 		// Status can be one of 3 options.  "New", "Replaced", "Rejected".
 		field.String("status"))
+
+	masterCounter = metric.NewCounter(
+		"luci/milo/buildbot_pubsub/masters",
+		"The number of buildbot master jsons received by Milo from PubSub",
+		nil,
+		field.Bool("internal"),
+		field.String("master"),
+		// Status can be one of 2 options.  "Success", "Failure".

[dsansome, 2016/10/16 23:45:36]

Convention is for these field values to be lower-case: "success", "failure"

[hinoka, 2016/10/17 21:35:13]

Done.

+		field.String("status"))
 )
 
 type pubSubMessage struct {
@@ -294,10 +303,12 @@ func PubSubHandler(ctx *router.Context) {
 		if err != nil {
 			logging.WithError(err).Errorf(
 				c, "Could not save master in datastore %s", err)
+			masterCounter.Add(c, 1, internal, master.Name, "Failure")

[dsansome, 2016/10/16 23:45:36]

Does master.Name have a "master." prefix?  If not it might be difficult to join
with other metrics.

[hinoka, 2016/10/17 21:35:13]

It does not, I assume it'd be better to normalize it by pre-pending "master."?

 			// This is transient, we do want PubSub to retry.
 			h.WriteHeader(500)
 			return
 		}
+		masterCounter.Add(c, 1, internal, master.Name, "Success")
 	}
 	h.WriteHeader(200)
 }