Troubleshooting Coherence Cluster Errors

Sometimes, a primary or secondary node may not start due to one of the following errors in the Oracle WebLogic Server log files:

• Warning (thread=Cluster, member=n/a): Received a discovery message that indicates the presence of an existing cluster that does not respond to join requests; this is usually caused by a network layer failure.

• Warning (thread=Cluster, member=n/a): Delaying formation of a new cluster; IpMonitor failed to verify the reachability of senior Member…
   …
   If this persists it is likely the result of a local or remote firewall rule blocking either ICMP pings, or connections to TCP port 7.

To overcome these errors, make sure that the DNS resolutions for the primary and secondary node machines lead to the same IP address when you ping the machines from the local system or from other systems.