node_not_connected_exception: Node is not connected
ElasticsearchWhat does it mean?
A node is currently not connected to another node it needs to communicate with. The request could not be forwarded to the target node because the intra-cluster (transport layer) connection was lost.
Why does it happen?
Network outage or packet loss, the target node crashing/restarting, a firewall/port block (default transport port 9300), the node becoming temporarily unresponsive due to GC pauses, or a DNS/host resolution problem. It can appear transiently during rolling restarts.
How to fix it
Inspect cluster and node health: use GET _cluster/health and GET _cat/nodes?v to see which node is missing. Verify inter-node network access and firewall rules for the transport port (9300). Check the affected node's logs for crashes, GC pauses or OOM. Review network stability and the discovery/seed host configuration.
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