Fix a bug introduced in Synapse v1.84.0 where workers do not start up when no `instance_map` was provided. (#15672)

* Fix #15669: always populate instance map even if it was empty

* Fix some tests

* Fix more tests

* Newsfile

Signed-off-by: Olivier Wilkinson (reivilibre) <oliverw@matrix.org>

* CI fix: don't forget to update apt repository sources before installing olddeps deps

* Add test testing the backwards compatibility

---------

Signed-off-by: Olivier Wilkinson (reivilibre) <oliverw@matrix.org>

8 files changed, 47 insertions, 5 deletions

diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 51cbeb3298..ce3a57fb01 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -314,6 +314,7 @@ jobs:
       # There aren't wheels for some of the older deps, so we need to install
       # their build dependencies
       - run: |
+          sudo apt-get -qq update
           sudo apt-get -qq install build-essential libffi-dev python-dev \
           libxml2-dev libxslt-dev xmlsec1 zlib1g-dev libjpeg-dev libwebp-dev
 
diff --git a/changelog.d/15672.bugfix b/changelog.d/15672.bugfix
new file mode 100644
index 0000000000..c81d7332b7
--- /dev/null
+++ b/changelog.d/15672.bugfix
@@ -0,0 +1 @@
+Fix a bug introduced in Synapse v1.84.0 where workers do not start up when no `instance_map` was provided.
\ No newline at end of file
diff --git a/synapse/config/workers.py b/synapse/config/workers.py
index d2311cc857..38e13dd7b5 100644
--- a/synapse/config/workers.py
+++ b/synapse/config/workers.py
@@ -222,7 +222,7 @@ class WorkerConfig(Config):
         # itself doesn't need this data as it would never have to talk to itself.
         instance_map: Dict[str, Any] = config.get("instance_map", {})
 
-        if instance_map and self.instance_name is not MAIN_PROCESS_INSTANCE_NAME:
+        if self.instance_name is not MAIN_PROCESS_INSTANCE_NAME:
             # The host used to connect to the main synapse
             main_host = config.get("worker_replication_host", None)
 
diff --git a/tests/app/test_homeserver_start.py b/tests/app/test_homeserver_start.py
index 788c935537..cd117b7394 100644
--- a/tests/app/test_homeserver_start.py
+++ b/tests/app/test_homeserver_start.py
@@ -25,6 +25,8 @@ class HomeserverAppStartTestCase(ConfigFileTestCase):
         # Add a blank line as otherwise the next addition ends up on a line with a comment
         self.add_lines_to_config(["  "])
         self.add_lines_to_config(["worker_app: test_worker_app"])
+        self.add_lines_to_config(["worker_replication_host: 127.0.0.1"])
+        self.add_lines_to_config(["worker_replication_http_port: 0"])
 
         # Ensure that starting master process with worker config raises an exception
         with self.assertRaises(ConfigError):
diff --git a/tests/app/test_openid_listener.py b/tests/app/test_openid_listener.py
index 2ee343d8a4..056d9402a4 100644
--- a/tests/app/test_openid_listener.py
+++ b/tests/app/test_openid_listener.py
@@ -42,6 +42,7 @@ class FederationReaderOpenIDListenerTests(HomeserverTestCase):
         # have to tell the FederationHandler not to try to access stuff that is only
         # in the primary store.
         conf["worker_app"] = "yes"
+        conf["instance_map"] = {"main": {"host": "127.0.0.1", "port": 0}}
 
         return conf
 
diff --git a/tests/config/test_workers.py b/tests/config/test_workers.py
index 49a6bdf408..086359fd71 100644
--- a/tests/config/test_workers.py
+++ b/tests/config/test_workers.py
@@ -17,7 +17,7 @@ from unittest.mock import Mock
 from immutabledict import immutabledict
 
 from synapse.config import ConfigError
-from synapse.config.workers import WorkerConfig
+from synapse.config.workers import InstanceLocationConfig, WorkerConfig
 
 from tests.unittest import TestCase
 
@@ -94,6 +94,7 @@ class WorkerDutyConfigTestCase(TestCase):
                 # so that it doesn't raise an exception here.
                 # (This is not read by `_should_this_worker_perform_duty`.)
                 "notify_appservices": False,
+                "instance_map": {"main": {"host": "127.0.0.1", "port": 0}},
             },
         )
 
@@ -138,7 +139,9 @@ class WorkerDutyConfigTestCase(TestCase):
         """
 
         main_process_config = self._make_worker_config(
-            worker_app="synapse.app.homeserver", worker_name=None
+            worker_app="synapse.app.homeserver",
+            worker_name=None,
+            extras={"instance_map": {"main": {"host": "127.0.0.1", "port": 0}}},
         )
 
         self.assertTrue(
@@ -203,6 +206,7 @@ class WorkerDutyConfigTestCase(TestCase):
                 # so that it doesn't raise an exception here.
                 # (This is not read by `_should_this_worker_perform_duty`.)
                 "notify_appservices": False,
+                "instance_map": {"main": {"host": "127.0.0.1", "port": 0}},
             },
         )
 
@@ -236,7 +240,9 @@ class WorkerDutyConfigTestCase(TestCase):
         Tests new config options. This is for the master's config.
         """
         main_process_config = self._make_worker_config(
-            worker_app="synapse.app.homeserver", worker_name=None
+            worker_app="synapse.app.homeserver",
+            worker_name=None,
+            extras={"instance_map": {"main": {"host": "127.0.0.1", "port": 0}}},
         )
 
         self.assertTrue(
@@ -262,7 +268,9 @@ class WorkerDutyConfigTestCase(TestCase):
         Tests new config options. This is for the worker's config.
         """
         appservice_worker_config = self._make_worker_config(
-            worker_app="synapse.app.generic_worker", worker_name="worker1"
+            worker_app="synapse.app.generic_worker",
+            worker_name="worker1",
+            extras={"instance_map": {"main": {"host": "127.0.0.1", "port": 0}}},
         )
 
         self.assertTrue(
@@ -298,6 +306,7 @@ class WorkerDutyConfigTestCase(TestCase):
             extras={
                 "notify_appservices_from_worker": "worker2",
                 "update_user_directory_from_worker": "worker1",
+                "instance_map": {"main": {"host": "127.0.0.1", "port": 0}},
             },
         )
         self.assertFalse(worker1_config.should_notify_appservices)
@@ -309,7 +318,33 @@ class WorkerDutyConfigTestCase(TestCase):
             extras={
                 "notify_appservices_from_worker": "worker2",
                 "update_user_directory_from_worker": "worker1",
+                "instance_map": {"main": {"host": "127.0.0.1", "port": 0}},
             },
         )
         self.assertTrue(worker2_config.should_notify_appservices)
         self.assertFalse(worker2_config.should_update_user_directory)
+
+    def test_worker_instance_map_compat(self) -> None:
+        """
+        Test that `worker_replication_*` settings are compatibly handled by
+        adding them to the instance map as a `main` entry.
+        """
+
+        worker1_config = self._make_worker_config(
+            worker_app="synapse.app.generic_worker",
+            worker_name="worker1",
+            extras={
+                "notify_appservices_from_worker": "worker2",
+                "update_user_directory_from_worker": "worker1",
+                "worker_replication_host": "127.0.0.42",
+                "worker_replication_http_port": 1979,
+            },
+        )
+        self.assertEqual(
+            worker1_config.instance_map,
+            {
+                "master": InstanceLocationConfig(
+                    host="127.0.0.42", port=1979, tls=False
+                ),
+            },
+        )
diff --git a/tests/replication/test_federation_ack.py b/tests/replication/test_federation_ack.py
index 12668b34c5..cf59b1a204 100644
--- a/tests/replication/test_federation_ack.py
+++ b/tests/replication/test_federation_ack.py
@@ -32,6 +32,7 @@ class FederationAckTestCase(HomeserverTestCase):
         config["worker_app"] = "synapse.app.generic_worker"
         config["worker_name"] = "federation_sender1"
         config["federation_sender_instances"] = ["federation_sender1"]
+        config["instance_map"] = {"main": {"host": "127.0.0.1", "port": 0}}
         return config
 
     def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
diff --git a/tests/storage/test_rollback_worker.py b/tests/storage/test_rollback_worker.py
index 966aafea6f..6861d3a6c9 100644
--- a/tests/storage/test_rollback_worker.py
+++ b/tests/storage/test_rollback_worker.py
@@ -55,6 +55,7 @@ class WorkerSchemaTests(HomeserverTestCase):
 
         # Mark this as a worker app.
         conf["worker_app"] = "yes"
+        conf["instance_map"] = {"main": {"host": "127.0.0.1", "port": 0}}
 
         return conf