Merge pull request cloudfoundry#67 from cloudfoundry/improve-description-of-diego-domain-metrics-162493639

Update description of Diego Domain freshness metrics

Author: ljarzynski

metrics/_diego.html.md.erb

@@ -48,8 +48,8 @@ Default Origin Name: bbs
  ConvergenceTasksPruned                                  | Cumulative number of times the BBS has deleted a malformed Task during its Task convergence pass. Emitted every 30 seconds.
  CrashedActualLRPs                                       | Total number of LRP instances that have crashed. Emitted every 30 seconds.
  CrashingDesiredLRPs                                     | Total number of DesiredLRPs that have at least one crashed instance. Emitted every 30 seconds.
- Domain.cf-apps                                          | Whether the 'cf-apps' domain is up-to-date, so that CF apps from CC have been synchronized with DesiredLRPs for Diego to run. `1` means the domain is up-to-date, no data means it is not. Emitted every 30 seconds.
- Domain.cf-tasks                                         | Whether the 'cf-tasks' domain is up-to-date, so that CF tasks from CC have been synchronized with tasks for Diego to run. `1` means the domain is up-to-date, no data means it is not. Emitted every 30 seconds.
+ Domain.cf-apps                                          | Whether the 'cf-apps' domain is up-to-date. Also known as [domain freshness](https://github.com/cloudfoundry/bbs/blob/master/doc/lrps.md#domain-freshness), this key metric indicates that CF apps from Cloud Controller have been synchronized with DesiredLRPs for Diego to run. When the domain is not up-to-date, Diego will **not** take corrective actions to ensure eventual consistency. In particular, Diego will refuse to stop extra app instances that have no corresponding desired state.<br><br> A value of `1` means the domain is up-to-date, **no data** means it is not. Emitted every 30 seconds.
+ Domain.cf-tasks                                         | Whether the 'cf-tasks' domain is up-to-date. Also known as [domain freshness](https://github.com/cloudfoundry/bbs/blob/master/doc/lrps.md#domain-freshness), this key metric indicates that CF tasks from Cloud Controller have been synchronized with Tasks for Diego to run. When the domain is not up-to-date, Diego will **not** take corrective actions to ensure eventual consistency.<br><br> A value of  `1` means the domain is up-to-date, **no data** means it is not.  Emitted every 30 seconds.
  ETCDLeader                                              | Index of the leader node in the etcd cluster. Emitted every 30 seconds.
  ETCDRaftTerm                                            | Raft term of the etcd cluster. Emitted every 30 seconds.
  ETCDReceivedBandwidthRate                               | Number of bytes per second received by the follower etcd node. Emitted every 30 seconds.