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Upgrade Troubleshooting - Elasticsearch

1. Introduction

Upgrading Elasticsearch is essential to benefit from new features, improvements, and security patches. However, upgrades can introduce issues if not handled properly. This guide covers troubleshooting steps to resolve common problems encountered during Elasticsearch upgrades.

2. Pre-upgrade Checklist

Before starting the upgrade process, ensure the following:

  • Backup your data and configuration files.
  • Review the release notes for breaking changes.
  • Test the upgrade in a staging environment.
  • Check plugin compatibility with the new version.

3. Common Issues and Solutions

3.1 Cluster Health Status

After upgrading, the cluster health status might show yellow or red.

Check the cluster health status:

GET /_cluster/health
{ "cluster_name": "elasticsearch", "status": "yellow", "timed_out": false, "number_of_nodes": 3, "number_of_data_nodes": 2, "active_primary_shards": 10, "active_shards": 18, "relocating_shards": 0, "initializing_shards": 0, "unassigned_shards": 2, "delayed_unassigned_shards": 0, "number_of_pending_tasks": 0, "number_of_in_flight_fetch": 0, "task_max_waiting_in_queue_millis": 0, "active_shards_percent_as_number": 90.0 }

Solution: Investigate the reasons for unassigned shards by checking the _cluster/allocation/explain API.

GET /_cluster/allocation/explain
{ "index": "my-index-000001", "shard": 0, "primary": true, "current_state": "unassigned", "unassigned_info": { "reason": "INDEX_CREATED", "at": "2023-10-01T12:00:00.000Z", "details": "index created", "last_allocation_status": "no_attempt" }, "can_allocate": "no", "allocate_explanation": "cannot allocate because allocation is not permitted to any of the nodes", "node_allocation_decisions": [ { "node_id": "node-1", "node_name": "node-1", "transport_address": "127.0.0.1:9300", "node_attributes": { "attr_name": "attr_value" }, "node_decision": "no", "deciders": [ { "decider": "same_shard", "decision": "NO", "explanation": "a copy of this shard is already allocated to this node" } ] } ] }

3.2 Node Not Joining the Cluster

If a node does not join the cluster after an upgrade, it could be due to version incompatibility or network issues.

Solution: Check the Elasticsearch logs for error messages. Ensure that all nodes in the cluster are compatible with the new version.

Sample log entry:

[2023-10-01T12:00:00,000][WARN ][o.e.d.z.ZenDiscovery ] [node-2] failed to send join request to master [{node-1}{node-1_id}{127.0.0.1}{127.0.0.1:9300}], reason [RemoteTransportException[[node-1][127.0.0.1:9300][internal:discovery/zen/join]]; nested: IllegalStateException[handshake failed]; ]

3.3 Plugin Issues

Incompatible plugins can cause failures during the upgrade. Ensure that all plugins are updated to their latest compatible versions.

Solution: List installed plugins and check their compatibility.

List installed plugins:

bin/elasticsearch-plugin list
analysis-icu discovery-ec2

Check plugin documentation for compatibility with the new Elasticsearch version.

4. Post-upgrade Steps

After a successful upgrade, perform the following steps:

  • Re-enable any settings or plugins disabled before the upgrade.
  • Run tests to ensure that the cluster is functioning correctly.
  • Monitor the cluster for any unusual behavior or performance issues.

5. Conclusion

Upgrading Elasticsearch can be challenging, but with proper preparation and troubleshooting, it can be done smoothly. Always backup your data, test in a staging environment, and monitor the cluster post-upgrade to ensure a successful transition.