add metadata section to docs
@@ -101,6 +101,13 @@ On each endpoint, the timeouts for communication are set as follows:
* The dial timeout by default is 30s, and can decrease automatically down to 100ms based on early results.
* The read timeout is static at 2s.
+## Metadata
+
+The forward plugin will publish the following metadata, if the *metadata*
+plugin is also enabled:
+
+* `forward/upstream`: the upstream used to forward the request
+
## Metrics
If monitoring is enabled (via the *prometheus* plugin) then the following metric are exported:
