am/DESIGN.md

# alert-manager

Alert manager converts Prometheus alerts into PubSub events which
are then used to drive the state in alert-manager.

```
        +-----------------------------+      +--------------------------+
        |  Prometheus (skia|buildbot) |      | Prometheus (skia|public) |
        +-------------+---------------+      +------------+-------------+
                                    |                                   |
                                    |                                   |
                           +--------v--------+                 +--------v--------+
                           |                 |                 |                 |
                           | alert-to-pubsub +-------+      +--+ alert-to-pubsub |
                           |                 |       |      |  |                 |
                           +-----------------+       |      |  +-----------------+
                                                     |      |
                                            +--------v------v----------+
                                            | PubSub                   |
                                            | Topic: prometheus-alerts |
                                            +---------------+----------+
                                              |
         +-----------------+                  |
         |                 |          +-------v-------+
         | Cloud Datastore <----------+               |
         |   IncidentAm    |          | alert-manager |
         |   SilenceAm     +---------->               |
         |                 |          +---------------+
         +-----------------+
```

The alert-manager application is state-less, all state is stored
in the Cloud Datastore. Also, all the logic for applying silences
to Incidents is done in the UI, i.e. the alert-manager backend
just reads and writes Incidents and Silences without looking at
the interactions between the two.