Added documentation for telemetry{ prometheus_retention_time = duration }

website/source/api/agent.html.md

@@ -238,13 +238,18 @@ This endpoint returns the configuration and member information of the local
 agent.
 
 | Method | Path                               | Produces                                   |
-| ------ | ---------------------------- | -------------------------- |
+| ------ | ---------------------------------- | ------------------------------------------ |
 | `GET`  | `/agent/metrics`                   | `application/json`                         |
+| `GET`  | `/agent/metrics?format=prometheus` | `text/plain; version=0.0.4; charset=utf-8` |
 
 This endpoint will dump the metrics for the most recent finished interval.
 For more information about metrics, see the [telemetry](/docs/agent/telemetry.html)
 page.
 
+In order to enable [Prometheus](https://prometheus.io/) support, you need to use the
+configuration directive
+[`prometheus_retention_time`](/docs/agent/options.html#telemetry-prometheus_retention_time).
+
 | Blocking Queries | Consistency Modes | ACL Required |
 | ---------------- | ----------------- | ------------ |
 | `NO`             | `none`            | `agent:read` |

website/source/docs/agent/options.html.md

@@ -1329,6 +1329,14 @@ Consul will not enable TLS for the HTTP API unless the `https` port has been ass
       is overlap between two rules, the more specific rule will take precedence. Blocking will take priority if the same
       prefix is listed multiple times.
 
+    * <a name="telemetry-prometheus_retention_time"></a><a href="telemetry-prometheus_retention_time">prometheus_retention_time</a>
+      If the value is greater than `0s` (the default), this enables [Prometheus](https://prometheus.io/) export of metrics.
+      The duration can be expressed using the duration semantics and will aggregates all counters for the duration specified
+      (it might have an impact on Consul's memory usage).
+      Fetching the metrics using prometheus can then be performed using the `/v1/agent/metrics?format=prometheus`.
+      The format is compatible natively with prometheus. When running in this mode, it is recommended to also enable the option
+      <a href="#telemetry-disable_hostname">`disable_hostname`</a> to avoid having prefixed metrics with hostname.
+
     * <a name="telemetry-enable_deprecated_names"></a><a href="#telemetry-enable_deprecated_names">`enable_deprecated_names`
       </a>Added in Consul 1.0, this enables old metric names of the format `consul.consul...` to be sent alongside
       other metrics. Defaults to false.

website/source/docs/agent/telemetry.html.md

@@ -23,7 +23,8 @@ Additionally, if the [`telemetry` configuration options](/docs/agent/options.htm
 are provided, the telemetry information will be streamed to a
 [statsite](http://github.com/armon/statsite) or [statsd](http://github.com/etsy/statsd) server where
 it can be aggregated and flushed to Graphite or any other metrics store. This
-information can also be viewed with the [metrics endpoint](/api/agent.html#view-metrics)
+information can also be viewed with the [metrics endpoint](/api/agent.html#view-metrics) in JSON
+format or using [Prometheus](https://prometheus.io/) format.
 
 Below is sample output of a telemetry dump: