* cluster: add alertmanager_cluster_messages_queued metric
* cluster: add metrics for sent messages
This change adds 2 new metrics:
- alertmanager_cluster_messages_sent_total
- alertmanager_cluster_messages_sent_size_total
* Fix marshaling for entries being broadcast
Individual notifications logs and silences being broadcast to the other
peers need to be encoded using the same length-delimited format as when
doing full-state synchronization.
* main: fix argument order for cluster.Join()
cluster.Join() was called with the push/pull and gossip interval
parameters being swapped one for another.
* Wait for the gossip to settle before sending notifications
See #1209 for details.
As an heuristic for mesh readyness, try to see if
the mesh looks stable (the number of peers isn't changing too much).
This implementation always mark the altermanager as ready after a maximum of 60s.
This adds one new flags to control this behavior:
```
--cluster.settle-timeout=60s mesh settling timeout. Do not wait more than this duration on startup.
```
It also adds `/-/ready` which always return 200 (in order to make it clear
that we are ready as soon as we can receive requests).
The mesh status is exposed in `/api/v1/status` and visible on `/#/status`.
* cluster: fix typos and base interval on gossipInterval
* cluster: gather alertmanager_peer_position all the time
This change moves the gathering of the alertmanager_peer_position metric
outside of the clusterWait() function so that the metric is computed
accurately even when no alerting group fires.
* cluster: add alertmanager_cluster_health_score metric
This metric is retrieved from the memberlist library.
Simon Pasquier
Corentin Chary
Fabian Reinartz