diff --git a/synapse/http/federation/well_known_resolver.py b/synapse/http/federation/well_known_resolver.py
index c846003886..5e9b0befb0 100644
--- a/synapse/http/federation/well_known_resolver.py
+++ b/synapse/http/federation/well_known_resolver.py
@@ -32,8 +32,8 @@ from synapse.util.metrics import Measure
# period to cache .well-known results for by default
WELL_KNOWN_DEFAULT_CACHE_PERIOD = 24 * 3600
-# jitter to add to the .well-known default cache ttl
-WELL_KNOWN_DEFAULT_CACHE_PERIOD_JITTER = 10 * 60
+# jitter factor to add to the .well-known default cache ttls
+WELL_KNOWN_DEFAULT_CACHE_PERIOD_JITTER = 0.1
# period to cache failure to fetch .well-known for
WELL_KNOWN_INVALID_CACHE_PERIOD = 1 * 3600
@@ -133,16 +133,14 @@ class WellKnownResolver(object):
# We have recently seen a valid well-known record for this
# server, so we cache the lack of well-known for a shorter time.
cache_period = WELL_KNOWN_DOWN_CACHE_PERIOD
- cache_period += random.uniform(
- 0, WELL_KNOWN_DEFAULT_CACHE_PERIOD_JITTER
- )
else:
- # add some randomness to the TTL to avoid a stampeding herd every hour
- # after startup
cache_period = WELL_KNOWN_INVALID_CACHE_PERIOD
- cache_period += random.uniform(
- 0, WELL_KNOWN_DEFAULT_CACHE_PERIOD_JITTER
- )
+
+ # add some randomness to the TTL to avoid a stampeding herd
+ cache_period *= random.uniform(
+ 1 - WELL_KNOWN_DEFAULT_CACHE_PERIOD_JITTER,
+ 1 + WELL_KNOWN_DEFAULT_CACHE_PERIOD_JITTER,
+ )
if cache_period > 0:
self._well_known_cache.set(server_name, result, cache_period)
@@ -194,7 +192,10 @@ class WellKnownResolver(object):
cache_period = WELL_KNOWN_DEFAULT_CACHE_PERIOD
# add some randomness to the TTL to avoid a stampeding herd every 24 hours
# after startup
- cache_period += random.uniform(0, WELL_KNOWN_DEFAULT_CACHE_PERIOD_JITTER)
+ cache_period *= random.uniform(
+ 1 - WELL_KNOWN_DEFAULT_CACHE_PERIOD_JITTER,
+ 1 + WELL_KNOWN_DEFAULT_CACHE_PERIOD_JITTER,
+ )
else:
cache_period = min(cache_period, WELL_KNOWN_MAX_CACHE_PERIOD)
cache_period = max(cache_period, WELL_KNOWN_MIN_CACHE_PERIOD)
diff --git a/tests/http/federation/test_matrix_federation_agent.py b/tests/http/federation/test_matrix_federation_agent.py
index 4d3f31d18c..c55aad8e11 100644
--- a/tests/http/federation/test_matrix_federation_agent.py
+++ b/tests/http/federation/test_matrix_federation_agent.py
@@ -551,7 +551,7 @@ class MatrixFederationAgentTests(TestCase):
self.assertEqual(self.well_known_cache[b"testserv"], b"target-server")
# check the cache expires
- self.reactor.pump((25 * 3600,))
+ self.reactor.pump((48 * 3600,))
self.well_known_cache.expire()
self.assertNotIn(b"testserv", self.well_known_cache)
@@ -639,7 +639,7 @@ class MatrixFederationAgentTests(TestCase):
self.assertEqual(self.well_known_cache[b"testserv"], b"target-server")
# check the cache expires
- self.reactor.pump((25 * 3600,))
+ self.reactor.pump((48 * 3600,))
self.well_known_cache.expire()
self.assertNotIn(b"testserv", self.well_known_cache)
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