ISSUE-14266: [2.8.1] Geo-Replication Broker sometimes cannot sync the updated clusters set.

[sijie]

Original Issue: apache/pulsar#14266

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Describe the bug I am using geo-replication on namespace level with version 2.8.1. Some time ago we changed the DNS record so the geo-replication failed. But there were already some topics created. When I try to update the geo-replication config with the following command:
bin/pulsar-admin clusters update ... bin/pulsar-admin namespaces set-clusters

The replication process does not recover as expected. I noticed in the log that the replicator still tries to connect to the outdated cluster URL.

While I managed to solve this by find the relevant broker and restart it, It seems there is some issue with config cache update?

To Reproduce Well I definitely failed to reproduce this, after broker restart, they could sync the update just fine. Probably try first with a failed replication config and then update with the right info.

Expected behavior Expect the change of replication clusters URL taken effect without need for server restart

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