Allow configuring a range for the account validity startup job

changelog.d/5276.feature

@@ -0,0 +1 @@
+Allow configuring a range for the account validity startup job.

docs/sample_config.yaml

@@ -753,7 +753,9 @@ uploads_path: "DATADIR/uploads"
 # This means that, if a validity period is set, and Synapse is restarted (it will
 # then derive an expiration date from the current validity period), and some time
 # after that the validity period changes and Synapse is restarted, the users'
-# expiration dates won't be updated unless their account is manually renewed.
+# expiration dates won't be updated unless their account is manually renewed. This
+# date will be randomly selected within a range [now + period ; now + period + d],
+# where d is equal to 10% of the validity period.
 #
 #account_validity:
 #  enabled: True

synapse/config/registration.py

@@ -39,6 +39,8 @@ def __init__(self, config, synapse_config):
             else:
                 self.renew_email_subject = "Renew your %(app)s account"
 
+            self.startup_job_max_delta = self.period * 10. / 100.
+
         if self.renew_by_email_enabled and "public_baseurl" not in synapse_config:
             raise ConfigError("Can't send renewal emails without 'public_baseurl'")
 
@@ -129,7 +131,9 @@ def default_config(self, generate_secrets=False, **kwargs):
         # This means that, if a validity period is set, and Synapse is restarted (it will
         # then derive an expiration date from the current validity period), and some time
         # after that the validity period changes and Synapse is restarted, the users'
-        # expiration dates won't be updated unless their account is manually renewed.
+        # expiration dates won't be updated unless their account is manually renewed. This
+        # date will be randomly selected within a range [now + period ; now + period + d],
+        # where d is equal to 10%% of the validity period.
         #
         #account_validity:
         #  enabled: True

synapse/storage/_base.py

@@ -16,6 +16,7 @@
 # limitations under the License.
 import itertools
 import logging
+import random
 import sys
 import threading
 import time
@@ -247,6 +248,8 @@ def __init__(self, db_conn, hs):
                 self._check_safe_to_upsert,
             )
 
+        self.rand = random.SystemRandom()
+
         if self._account_validity.enabled:
             self._clock.call_later(
                 0.0,
@@ -308,21 +311,36 @@ def select_users_with_no_expiration_date_txn(txn):
             res = self.cursor_to_dict(txn)
             if res:
                 for user in res:
-                    self.set_expiration_date_for_user_txn(txn, user["name"])
+                    self.set_expiration_date_for_user_txn(
+                        txn,
+                        user["name"],
+                        use_delta=True,
+                    )
 
         yield self.runInteraction(
             "get_users_with_no_expiration_date",
             select_users_with_no_expiration_date_txn,
         )
 
-    def set_expiration_date_for_user_txn(self, txn, user_id):
+    def set_expiration_date_for_user_txn(self, txn, user_id, use_delta=False):
         """Sets an expiration date to the account with the given user ID.
 
         Args:
              user_id (str): User ID to set an expiration date for.
+             use_delta (bool): If set to False, the expiration date for the user will be
+                now + validity period. If set to True, this expiration date will be a
+                random value in the [now + period; now + period + d] range, d being a
+                delta equal to 10% of the validity period.
         """
         now_ms = self._clock.time_msec()
         expiration_ts = now_ms + self._account_validity.period
+
+        if use_delta:
+            expiration_ts = self.rand.randrange(
+                expiration_ts,
+                expiration_ts + self._account_validity.startup_job_max_delta,
+            )
+
         self._simple_insert_txn(
             txn,
             "account_validity",

tests/rest/client/v2_alpha/test_register.py

@@ -436,6 +436,7 @@ class AccountValidityBackgroundJobTestCase(unittest.HomeserverTestCase):
 
     def make_homeserver(self, reactor, clock):
         self.validity_period = 10
+        self.max_delta = self.validity_period * 10. / 100.
 
         config = self.default_config()
 
@@ -453,14 +454,18 @@ def make_homeserver(self, reactor, clock):
 
     def test_background_job(self):
         """
-        Tests whether the account validity startup background job does the right thing,
-        which is sticking an expiration date to every account that doesn't already have
-        one.
+        Tests the same thing as test_background_job, except that it sets the
+        startup_job_max_delta parameter and checks that the expiration date is within the
+        allowed range.
         """
-        user_id = self.register_user("kermit", "user")
+        user_id = self.register_user("kermit_delta", "user")
+
+        self.hs.config.account_validity.startup_job_max_delta = self.max_delta
 
         now_ms = self.hs.clock.time_msec()
         self.get_success(self.store._set_expiration_date_when_missing())
 
         res = self.get_success(self.store.get_expiration_ts_for_user(user_id))
-        self.assertEqual(res, now_ms + self.validity_period)
+
+        self.assertLessEqual(res, now_ms + self.validity_period + self.max_delta)
+        self.assertGreaterEqual(res, now_ms + self.validity_period)