Add listener health (#14747)

Fixes: #8780

changelog.d/14747.feature

@@ -0,0 +1 @@
+Add a dedicated listener configuration for `health` endpoint.

docs/usage/configuration/config_documentation.md

@@ -480,6 +480,12 @@ Valid resource names are:
 
 * `static`: static resources under synapse/static (/_matrix/static). (Mostly useful for 'fallback authentication'.)
 
+* `health`: the [health check endpoint](../../reverse_proxy.md#health-check-endpoint). This endpoint
+ is by default active for all other resources and does not have to be activated separately.
+ This is only useful if you want to use the health endpoint explicitly on a dedicated port or
+ for [workers](../../workers.md) and containers without listener e.g.
+ [application services](../../workers.md#notifying-application-services).
+
 Example configuration #1:
 ```yaml
 listeners:

synapse/app/generic_worker.py

@@ -199,6 +199,9 @@ def _listen_http(self, listener_config: ListenerConfig) -> None:
  "A 'media' listener is configured but the media"
  " repository is disabled. Ignoring."
  )
+ elif name == "health":
+ # Skip loading, health resource is always included
+ continue
 
  if name == "openid" and "federation" not in res.names:
  # Only load the openid resource separately if federation resource

synapse/app/homeserver.py

@@ -96,6 +96,9 @@ def _listener_http(
  # Skip loading openid resource if federation is defined
  # since federation resource will include openid
  continue
+ if name == "health":
+ # Skip loading, health resource is always included
+ continue
  resources.update(self._configure_named_resource(name, res.compress))
 
  additional_resources = listener_config.http_options.additional_resources