Enable exposure of Prometheus metrics.

roles/matrix-synapse/defaults/main.yml

@@ -13,6 +13,9 @@ matrix_synapse_container_expose_client_server_api_port: false
 # Controls whether the Appservice IRC container exposes the Client/Server API port (tcp/9999).
 matrix_appservice_irc_container_expose_client_server_api_port: false
 
+# Controls whether the matrix-synapse container exposes the metrics port (tcp/9100).
+matrix_synapse_container_expose_metrics_port: false
+
 # List of systemd services that matrix-synapse.service depends on
 matrix_synapse_systemd_required_services_list: ['docker.service']
 
@@ -118,6 +121,11 @@ matrix_synapse_app_service_config_files: []
 # any password providers have been enabled or not.
 matrix_synapse_password_providers_enabled: false
 
+# Enable exposure of metrics to Prometheus
+# See https://github.com/matrix-org/synapse/blob/master/docs/metrics-howto.rst
+matrix_synapse_metrics_enabled: false
+matrix_synapse_metrics_port: 9100
+
 # Postgres database information
 matrix_synapse_database_host: ""
 matrix_synapse_database_user: ""

roles/matrix-synapse/templates/synapse/homeserver.yaml.j2

@@ -127,6 +127,12 @@ federation_domain_whitelist: {{ matrix_synapse_federation_domain_whitelist|to_js
 # List of ports that Synapse should listen on, their purpose and their
 # configuration.
 listeners:
+{% if matrix_synapse_metrics_enabled %}
+  - type: metrics
+    port: {{ matrix_synapse_metrics_port }}
+    bind_addresses:
+      - '0.0.0.0'
+{% endif %}
 {% if matrix_synapse_federation_enabled %}
   # Main HTTPS listener
   # For when matrix traffic is sent directly to synapse.
@@ -496,7 +502,7 @@ autocreate_auto_join_rooms: {{ matrix_synapse_autocreate_auto_join_rooms }}
 ## Metrics ###
 
 # Enable collection and rendering of performance metrics
-enable_metrics: False
+enable_metrics: {{ matrix_synapse_metrics_enabled }}
 report_stats: {{ matrix_synapse_report_stats|to_json }}
 
 

roles/matrix-synapse/templates/synapse/systemd/matrix-synapse.service.j2

@@ -34,6 +34,9 @@ ExecStart=/usr/bin/docker run --rm --name matrix-synapse \
 			{% if matrix_synapse_container_expose_client_server_api_port %}
 			-p 127.0.0.1:8008:8008 \
 			{% endif %}
+			{% if matrix_synapse_container_expose_metrics_port %}
+			-p 127.0.0.1:{{ matrix_synapse_metrics_port }}:{{ matrix_synapse_metrics_port }} \
+			{% endif %}
 			-v {{ matrix_synapse_config_dir_path }}:/data:ro \
 			-v {{ matrix_synapse_run_path }}:/matrix-run:rw \
 			-v {{ matrix_synapse_base_path }}/storage:/matrix-media-store-parent:slave \