Add support for multiple federation sender workers

CHANGELOG.md

@@ -4,7 +4,8 @@
 
 People who are interested in running a Synapse worker setup should know that **our Synapse worker implementation is much more powerful now**:
 
-- we've added [Stream writers support](#stream-writers-support)
+- we've added support for [Stream writers](#stream-writers-support)
+- we've added support for [multiple federation sender workers](#multiple-federation-sender-workers-support)
 - see the [Potential Backward Incompatibilities after these Synapse worker changes](#potential-backward-incompatibilities-after-these-synapse-worker-changes)
 
 ### Stream writers support
@@ -26,6 +27,11 @@ matrix_synapse_workers_stream_writer_receipts_stream_workers_count: 1
 matrix_synapse_workers_stream_writer_presence_stream_workers_count: 1
 ```
 
+### Multiple federation sender workers support
+
+Until now, we only supported a single `federation_sender` worker (`matrix_synapse_workers_federation_sender_workers_count` could either be `0` or `1`).
+From now on, you can have as many as you want to help with your federation traffic.
+
 ### Potential Backward Incompatibilities after these Synapse worker changes
 
 Below we'll discuss **potential backward incompatibilities**.

roles/matrix-synapse/defaults/main.yml

@@ -510,12 +510,21 @@ matrix_synapse_workers_pusher_workers_metrics_range_start: 19200
 matrix_synapse_workers_appservice_workers_count: 0
 matrix_synapse_workers_appservice_workers_metrics_range_start: 19300
 
-# matrix_synapse_workers_federation_sender_workers_count can only be 0 or 1 for now.
+# matrix_synapse_workers_federation_sender_workers_count controls the number of federation sender workers to spawn.
-# More instances are not supported due to a playbook limitation having to do with keeping `federation_sender_instances` in `homeserver.yaml` updated.
 # See https://github.com/matrix-org/synapse/blob/master/docs/workers.md#synapseappfederation_sender
 matrix_synapse_workers_federation_sender_workers_count: "{{ matrix_synapse_workers_presets[matrix_synapse_workers_preset]['federation_sender_workers_count'] }}"
 matrix_synapse_workers_federation_sender_workers_metrics_range_start: 19400
 
+# matrix_synapse_federation_sender_instances populates the `federation_sender_instances` Synapse configuration used when Synapse workers are in use (`matrix_synapse_workers_enabled`).
+# What you see below is an initial default value which will be adjusted at runtime based on the value of `matrix_synapse_workers_federation_sender_workers_count` or `matrix_synapse_workers_enabled_list`.
+# Adjusting this value manually is generally not necessary.
+matrix_synapse_federation_sender_instances: []
+
+# matrix_synapse_send_federation controls if theh main Synapse process should send federation traffic.
+# This is allowed if workers are disabled, or if there are no federation sender workers.
+# Adjusting this value manually is generally not necessary.
+matrix_synapse_send_federation: "{{ not matrix_synapse_workers_enabled or (matrix_synapse_workers_enabled_list | selectattr('type', 'equalto', 'federation_sender') | list | length > 0) }}"
+
 matrix_synapse_workers_media_repository_workers_count: "{{ matrix_synapse_workers_presets[matrix_synapse_workers_preset]['media_repository_workers_count'] }}"
 matrix_synapse_workers_media_repository_workers_port_range_start: 18551
 matrix_synapse_workers_media_repository_workers_metrics_range_start: 19551

roles/matrix-synapse/tasks/synapse/workers/init.yml

@@ -53,6 +53,13 @@
   register: "matrix_synapse_workers_list_results_federation_sender_workers"
   loop: "{{ range(0, matrix_synapse_workers_federation_sender_workers_count | int) | list }}"
 
+- name: Populate matrix_synapse_federation_sender_instances from enabled federation sender workers list
+  ansible.builtin.set_fact:
+    matrix_synapse_federation_sender_instances: "{{ matrix_synapse_federation_sender_instances + [item.ansible_facts.worker.name] }}"
+  with_items: "{{ matrix_synapse_workers_list_results_federation_sender_workers.results }}"
+
+- debug: var="matrix_synapse_federation_sender_instances"
+
 # This type of worker can only have a count of 1, at most
 - name: Build pusher workers
   ansible.builtin.set_fact:

roles/matrix-synapse/tasks/validate_config.yml

@@ -31,7 +31,6 @@
   when: "vars[item]|int > 1"
   with_items:
     - "matrix_synapse_workers_pusher_workers_count"
-    - "matrix_synapse_workers_federation_sender_workers_count"
     - "matrix_synapse_workers_stream_writer_typing_stream_workers_count"
     - "matrix_synapse_workers_stream_writer_to_device_stream_workers_count"
     - "matrix_synapse_workers_stream_writer_account_data_stream_workers_count"

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

@@ -352,9 +352,6 @@ worker_app: synapse.app.homeserver
 
 # thx https://oznetnerd.com/2017/04/18/jinja2-selectattr-filter/
 # reduce the main worker's offerings to core homeserver business
-{% if matrix_synapse_workers_enabled_list | selectattr('type', 'equalto', 'federation_sender') | list | length > 0  %}
-send_federation: false
-{% endif %}
 {% if matrix_synapse_workers_enabled_list | selectattr('type', 'equalto', 'media_repository') | list | length > 0  %}
 enable_media_repo: false
 {% endif %}
@@ -2851,6 +2848,7 @@ opentracing:
 # Uncomment if using a federation sender worker.
 #
 #send_federation: false
+send_federation: {{ matrix_synapse_send_federation | to_json }}
 
 # It is possible to run multiple federation sender workers, in which case the
 # work is balanced across them.
@@ -2862,6 +2860,7 @@ opentracing:
 #
 #federation_sender_instances:
 #  - federation_sender1
+federation_sender_instances: {{ matrix_synapse_federation_sender_instances | to_json }}
 
 # When using workers this should be a map from `worker_name` to the
 # HTTP replication listener of the worker, if configured.