Also jitter the invalid cache period

synapse/http/federation/matrix_federation_agent.py

@@ -296,16 +296,18 @@ class MatrixFederationAgent(object):
             response = yield make_deferred_yieldable(
                 self._well_known_agent.request(b"GET", uri),
             )
+            body = yield make_deferred_yieldable(readBody(response))
+            if response.code != 200:
+                raise Exception("Non-200 response %s", response.code)
         except Exception as e:
-            logger.info("Connection error fetching %s: %s", uri_str, e)
-            self._well_known_cache.set(server_name, None, WELL_KNOWN_INVALID_CACHE_PERIOD)
-            defer.returnValue(None)
+            logger.info("Error fetching %s: %s", uri_str, e)
 
-        body = yield make_deferred_yieldable(readBody(response))
+            # 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)
 
-        if response.code != 200:
-            logger.info("Error response %i from %s", response.code, uri_str)
-            self._well_known_cache.set(server_name, None, WELL_KNOWN_INVALID_CACHE_PERIOD)
+            self._well_known_cache.set(server_name, None, cache_period)
             defer.returnValue(None)
 
         try:
@@ -326,8 +328,8 @@ class MatrixFederationAgent(object):
         )
         if cache_period is None:
             cache_period = WELL_KNOWN_DEFAULT_CACHE_PERIOD
-            # add some randomness to the TTL to avoid a stampeding herd every hour after
-            # startup
+            # 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)
         else:
             cache_period = min(cache_period, WELL_KNOWN_MAX_CACHE_PERIOD)