throw together a quick ref of what is monitored by prometheus

`scrape_configs`, in `prometheus.yml`, from Puppet, in

`profile::prometheus::server`.

## Monitored services

Those are the actual services monitored by Prometheus.

### Internal server (prometheus1)

The "internal" server scrapes all hosts managed by Puppet for

TPA. Puppet installs a [`node_exporter`](https://github.com/prometheus/node_exporter) on *all* servers, which

takes care of metrics like CPU, memory, disk usage, time accuracy, and

so on. Then other exporters might be enabled on specific services,

like email or web servers.

Access to the internal server is fairly public: the metrics there are

not considered to be security sensitive and protected by

authentication only to keep bots away.

### External server (prometheus2)

The "external" server, on the other hand, is more restrictive and does

not allow public access. This is out of concern that specific metrics

might lead to timing attacks against the network and/or leak sensitive

information. The external server also explicitly does *not* scrape TPA

servers automatically: it only scrapes certain services that are

manually configured by TPA.

Those are the services currently monitored by the external server:

 * [bridgestrap](https://bridges.torproject.org/bridgestrap-metrics)

 * [rdsys](https://bridges.torproject.org/rdsys-backend-metrics)

 * OnionPerf external nodes' `node_exporter`s

 * connectivity test on (some?) bridges (using the

   [`blackbox_exporter`](https://github.com/prometheus/blackbox_exporter/))

## SLA

Prometheus is currently not doing alerting so it doesn't have any sort