Add some cross references to worker documentation (#13974)

Signed-off-by: Dirk Klimpel <dirk@klimpel.org>

changelog.d/13974.doc

+Add some cross references to worker documentation.

docs/systemd-with-workers/workers/media_worker.yaml

+worker_app: synapse.app.media_repository
+worker_name: media_worker
+
+# The replication listener on the main synapse process.
+worker_replication_host: 127.0.0.1
+worker_replication_http_port: 9093
+
+worker_listeners:
+  - type: http
+    port: 8085
+    resources:
+      - names: [media]
+
+worker_log_config: /etc/matrix-synapse/media-worker-log.yaml

docs/workers.md

@@ -93,7 +93,6 @@ listener" for the main process; and secondly, you need to enable redis-based
 replication. Optionally, a shared secret can be used to authenticate HTTP
 traffic between workers. For example:
 
-
 ```yaml
 # extend the existing `listeners` section. This defines the ports that the
 # main process will listen on.
@@ -129,7 +128,8 @@ In the config file for each worker, you must specify:
  * The HTTP replication endpoint that it should talk to on the main synapse process
    (`worker_replication_host` and `worker_replication_http_port`)
  * If handling HTTP requests, a `worker_listeners` option with an `http`
-   listener, in the same way as the `listeners` option in the shared config.
+   listener, in the same way as the [`listeners`](usage/configuration/config_documentation.md#listeners)
+   option in the shared config.
  * If handling the `^/_matrix/client/v3/keys/upload` endpoint, the HTTP URI for
    the main process (`worker_main_http_uri`).
 
@@ -285,8 +285,9 @@ For multiple workers not handling the SSO endpoints properly, see
 [#7530](https://github.com/matrix-org/synapse/issues/7530) and
 [#9427](https://github.com/matrix-org/synapse/issues/9427).
 
-Note that a HTTP listener with `client` and `federation` resources must be
-configured in the `worker_listeners` option in the worker config.
+Note that a [HTTP listener](usage/configuration/config_documentation.md#listeners)
+with `client` and `federation` `resources` must be configured in the `worker_listeners`
+option in the worker config.
 
 #### Load balancing
 
@@ -326,7 +327,8 @@ effects of bursts of events from that bridge on events sent by normal users.
 Additionally, the writing of specific streams (such as events) can be moved off
 of the main process to a particular worker.
 
-To enable this, the worker must have a HTTP replication listener configured,
+To enable this, the worker must have a
+[HTTP `replication` listener](usage/configuration/config_documentation.md#listeners) configured,
 have a `worker_name` and be listed in the `instance_map` config. The same worker
 can handle multiple streams, but unless otherwise documented, each stream can only
 have a single writer.
@@ -410,7 +412,7 @@ the stream writer for the `presence` stream:
 There is also support for moving background tasks to a separate
 worker. Background tasks are run periodically or started via replication. Exactly
 which tasks are configured to run depends on your Synapse configuration (e.g. if
-stats is enabled).
+stats is enabled). This worker doesn't handle any REST endpoints itself.
 
 To enable this, the worker must have a `worker_name` and can be configured to run
 background tasks. For example, to move background tasks to a dedicated worker,
@@ -457,8 +459,8 @@ worker application type.
 #### Notifying Application Services
 
 You can designate one generic worker to send output traffic to Application Services.
-
-Specify its name in the shared configuration as follows:
+Doesn't handle any REST endpoints itself, but you should specify its name in the
+shared configuration as follows:
 
 ```yaml
 notify_appservices_from_worker: worker_name
@@ -536,16 +538,12 @@ file to stop the main synapse running background jobs related to managing the
 media repository. Note that doing so will prevent the main process from being
 able to handle the above endpoints.
 
-In the `media_repository` worker configuration file, configure the http listener to
+In the `media_repository` worker configuration file, configure the
+[HTTP listener](usage/configuration/config_documentation.md#listeners) to
 expose the `media` resource. For example:
 
 ```yaml
-worker_listeners:
- - type: http
-   port: 8085
-   resources:
-     - names:
-       - media
+{{#include systemd-with-workers/workers/media_worker.yaml}}
 ```
 
 Note that if running multiple media repositories they must be on the same server