[CASSANDRA-19722] Metric for Cross Node DC Latency records external DCs as UNKNOWN_DC until restart

• Type: Bug
• Status: Open
• Priority: Normal
• Resolution: Unresolved
• Fix Version/s: 4.1.x, 5.0.x, 5.x
• Component/s: Observability/Metrics
• Bug Category: Correctness
• Severity: Normal
• Complexity: Normal
• Discovered By: User Report
• Platform: All
• Assignee: Unassigned
• Reporter: Andrew
• Created: 21/Jun/24 11:16
• Updated: 13/Oct/24 19:32

Description

When creating a new DC for a different region (In this case, on AWS), I've noticed that the metric (JMX Exporter): `org.apache.cassandra.metrics:type=Messaging,name=*-Latency` shows `UNKNOWN_DC` for external datacenters until the node is restarted, at which point it seems to resolve to the actual datacenter name.

I'm using GossipingFileSnitch and nodetool status and nodetool gossipinfo always show the correct DC for the nodes, which makes me suspect there's some variable that's responsible for the metric that isn't updated