These diagnostic alerts indicate when a node leaves the cluster, and when a node joins the cluster. 

The following appears in the application log:

INFO ; HAZELCAST ; HAZELCAST-1001 ; Node joined the cluster ; not-detected ;  ;  ; {"member":"Member [...]:... - ..."}

WARNING ; HAZELCAST ; HAZELCAST-1002 ; Node left the cluster ; not-detected ;  ;  ; {"member":"Member [...]:... - ..."}

These alerts are enabled by default in Confluence 6.11 or later. 

To resolve this issue

There's no action required for these alerts. 

However, this information may be helpful when determining the chain of events that lead to an outage or other issue. 

What will happen if I ignore this alert? 

These alerts are for information only. There's no action required. 

Can I change the threshold of this alert?

These alerts are not configurable.