Introduction

Redis cluster fails when not all slots covered by nodes. This guide provides step-by-step diagnosis and resolution.

Symptoms

Typical error output:

bash
Error: Database operation failed
Check database logs for details
Verify connectivity and configuration

Common Causes

  1. 1.Service not running or unreachable
  2. 2.Memory or disk resource exhausted
  3. 3.Cluster or replication configuration issue
  4. 4.Authentication or permission denied

Step-by-Step Fix

Step 1: Check Current State

bash
# Check service status
systemctl status elasticsearch mongod redis
# View logs
journalctl -u elasticsearch -n 50
# Check cluster status
curl localhost:9200/_cluster/health

Step 2: Identify Root Cause

bash
# Check service logs
journalctl -u <service> -n 50
# Verify configuration
cat /etc/<service>/<service>.conf
# Check resources
free -m && df -h

Step 3: Apply Primary Fix

```bash # Primary fix: Check and restart # Check service systemctl status elasticsearch

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

# Restart if needed systemctl restart elasticsearch ```

Step 4: Apply Alternative Fix

```bash # Alternative: Check configuration # View logs tail -f /var/log/elasticsearch/cluster.log

# Check memory free -m && df -h

# Verify configuration cat /etc/elasticsearch/elasticsearch.yml ```

Step 5: Verify the Fix

bash
curl localhost:9200/_cluster/health?pretty
# status should be "green" or "yellow"
systemctl status elasticsearch

Common Pitfalls

  • Not monitoring memory usage
  • Using default JVM heap settings
  • Ignoring cluster health status
  • Not testing failover scenarios

Best Practices

  • Monitor cluster health continuously
  • Set appropriate memory limits
  • Regular backup and restore testing
  • Keep software versions updated
  • Cluster Status Error
  • Memory Exhausted
  • Replication Failed
  • Query Timeout