Merge pull request #27173 from akka/wip-27172-increase-fd-nodes-patriknw

akka-cluster/src/main/resources/reference.conf

@@ -209,7 +209,7 @@ akka {
 
       # Number of member nodes that each member will send heartbeat messages to,
       # i.e. each node will be monitored by this number of other nodes.
-      monitored-by-nr-of-members = 5
+      monitored-by-nr-of-members = 9
       
       # After the heartbeat request has been sent the first failure detection
       # will start after this period, even though no heartbeat message has

akka-cluster/src/test/scala/akka/cluster/ClusterConfigSpec.scala

@@ -37,7 +37,7 @@ class ClusterConfigSpec extends AkkaSpec {
       GossipInterval should ===(1 second)
       GossipTimeToLive should ===(2 seconds)
       HeartbeatInterval should ===(1 second)
-      MonitoredByNrOfMembers should ===(5)
+      MonitoredByNrOfMembers should ===(9)
       HeartbeatExpectedResponseAfter should ===(1 seconds)
       LeaderActionsInterval should ===(1 second)
       UnreachableNodesReaperInterval should ===(1 second)

akka-docs/src/main/paradox/project/migration-guide-2.5.x-2.6.x.md

@@ -279,6 +279,17 @@ more dead letters in Akka 2.5. In Akka 2.6 the count is reset after configured `
 
 `akka.log-dead-letters-during-shutdown` default configuration changed from `on` to `off`.
 
+### Cluster failure detection
+
+Default number of nodes that each node is observing for failure detection has increased from 5 to 9.
+The reason is to have better coverage and unreachability information for downing decisions.
+
+Configuration property:
+
+```
+akka.cluster.monitored-by-nr-of-members = 9
+```
+
 ## Source incompatibilities
 
 ### StreamRefs