Elasticsearch Version Upgrade Instability

Elasticsearch version upgrades can cause temporary or persistent cluster instability. This guide helps identify and resolve common issues that occur during and after upgrades.

Pre-Upgrade Preparation

Verify Upgrade Path

Elasticsearch supports direct upgrades only between specific versions:

Pre-Upgrade Checks

GET /_cat/health?v
GET /_cat/nodes?v
GET /_cluster/settings
GET /_migration/deprecations

Ensure:

• Cluster is green
• All nodes at same version
• No deprecated features in use

Common Upgrade Issues

Issue 1: Mixed Version Cluster Instability

Symptoms:

• Increased latency during rolling upgrade
• Shard allocation delays
• Query failures

Causes:

• Nodes running different versions
• Version-specific optimizations disabled

Solutions:

1. Complete the upgrade quickly:

   • Don't leave cluster in mixed-version state
   • Upgrade during low-traffic periods

2. Disable allocation during node restart:

PUT /_cluster/settings
{
  "transient": {
    "cluster.routing.allocation.enable": "primaries"
  }
}

3. Re-enable after node rejoins:

PUT /_cluster/settings
{
  "transient": {
    "cluster.routing.allocation.enable": "all"
  }
}

Issue 2: Node Won't Join After Upgrade

Symptoms:

• Upgraded node doesn't appear in cluster
• "incompatible" errors in logs

Diagnosis:

grep -i "incompatible\|version" /var/log/elasticsearch/*.log

Solutions:

1. Check version compatibility:

GET /_cat/nodes?v&h=name,version

2. Verify transport protocol compatibility:

   • Ensure network.host and discovery settings match

3. Clear node state if corrupt:

# Last resort - data on this node will be lost
rm -rf /var/lib/elasticsearch/nodes/0/_state

Issue 3: Shard Recovery Delays

Symptoms:

• Yellow cluster status persists
• Slow shard allocation

Causes:

• Recovery happening across version boundary
• New segment format compatibility

Solutions:

1. Increase recovery settings temporarily:

PUT /_cluster/settings
{
  "transient": {
    "indices.recovery.max_bytes_per_sec": "500mb",
    "cluster.routing.allocation.node_concurrent_recoveries": 4
  }
}

2. Monitor recovery progress:

GET /_cat/recovery?v&active_only=true

Issue 4: Index Compatibility Issues

Symptoms:

• Old indices not accessible
• "too old" or "incompatible" errors

Diagnosis:

GET /_cat/indices?v&h=index,version.created

Solutions:

For indices from incompatible versions:

// Reindex to new index
POST _reindex
{
  "source": {"index": "old-index"},
  "dest": {"index": "new-index"}
}

// Delete old index
DELETE /old-index

Issue 5: Plugin Failures

Symptoms:

• Node won't start
• Plugin errors in logs

Diagnosis:

grep -i "plugin" /var/log/elasticsearch/*.log

Solutions:

1. Remove incompatible plugins:

bin/elasticsearch-plugin remove plugin-name

2. Install compatible versions:

bin/elasticsearch-plugin install plugin-name

Issue 6: Performance Regression

Symptoms:

• Slower queries after upgrade
• Higher resource usage

Causes:

• New default settings
• Different query execution
• New security overhead

Solutions:

1. Review changed defaults:

   • Check release notes for default changes
   • Explicitly set critical settings

2. Profile slow queries:

{
  "profile": true,
  "query": {...}
}

3. Compare settings:

GET /_cluster/settings?include_defaults=true

Rolling Upgrade Procedure

Step 1: Disable Shard Allocation

PUT /_cluster/settings
{
  "transient": {
    "cluster.routing.allocation.enable": "primaries"
  }
}

Step 2: Stop Indexing (Optional)

For critical systems, pause indexing to ensure consistency.

Step 3: Perform Sync Flush (ES 7.x)

POST /_flush/synced

Step 4: Stop and Upgrade Node

systemctl stop elasticsearch
# Install new version
rpm -Uvh elasticsearch-8.x.rpm
# or
dpkg -i elasticsearch-8.x.deb

Step 5: Start Node

systemctl start elasticsearch

Step 6: Wait for Node to Join

GET /_cat/nodes?v
GET /_cat/health?v

Step 7: Re-enable Allocation

PUT /_cluster/settings
{
  "transient": {
    "cluster.routing.allocation.enable": "all"
  }
}

Step 8: Wait for Green

GET /_cluster/health?wait_for_status=green&timeout=5m

Step 9: Repeat for Each Node

Post-Upgrade Verification

Health Checks

# Cluster health
curl -X GET "localhost:9200/_cluster/health?pretty"

# Node versions
curl -X GET "localhost:9200/_cat/nodes?v&h=name,version"

# Index health
curl -X GET "localhost:9200/_cat/indices?v&health=yellow,red"

Performance Baseline

• Compare query latencies to pre-upgrade
• Monitor resource usage
• Check error rates

Rollback Planning

Before Upgrade

1. Take snapshots:

PUT /_snapshot/backup/pre-upgrade
{
  "indices": "*",
  "include_global_state": true
}

2. Document current configuration
3. Keep old binaries available

If Rollback Needed

1. Stop upgraded nodes
2. Restore from snapshot to old version cluster
3. Investigate issues before reattempting

Related Topics

• Elasticsearch 8.x Breaking Changes Cluster Issues
• Elasticsearch Rolling Restart Problems
• Elasticsearch Master Not Discovered Diagnosis