Graylog Index Rotation Failure — Quick Fix

In this tutorial, you'll learn about Graylog Index Rotation Failure. We cover key concepts, practical examples, and best practices.

The Problem

Graylog cannot rotate the current write index. The index may be full, the Elasticsearch cluster may be unhealthy, or the rotation strategy configuration may be misconfigured. Messages may stop being indexed entirely.

Error example:

Graylog index rotation failed: Cannot write to index 'graylog_0'
Elasticsearch cluster status is RED — cannot rotate
Index rotation blocked: disk space below threshold

The Fix

Step 1: Check Elasticsearch cluster health

WRONG — manually forcing index rotation:

# Forcing rotation will fail if Elasticsearch is unhealthy

RIGHT — check and repair Elasticsearch first:

# Check cluster health
curl http://elasticsearch:9200/_cluster/health

Output:

{"status": "red", "timed_out": false, "number_of_nodes": 3}

If status is yellow or red, fix Elasticsearch first. Common fixes include re-allocating unassigned shards or clearing disk thresholds:

curl -X PUT http://elasticsearch:9200/_cluster/settings \
  -d '{"transient": {"cluster.routing.allocation.disk.watermark.low": "90%"}}'

Step 2: Check the rotation strategy

WRONG — using index time-based rotation with too-short intervals:

# Rotating too frequently creates many small indices

RIGHT — configure appropriate rotation settings:

In Graylog web UI:
System -> Indices -> [Index Set] -> Edit
- Index rotation strategy: Size-based (default 1 GB)
- Index retention strategy: Delete (keep last 30)
- Elasticsearch shards: 4
- Elasticsearch replicas: 1

Use DodaTech's Graylog Index Health Monitor to track index sizes, rotation timing, and Elasticsearch storage utilization.

Prevention Tips

• Use size-based rotation (1-5 GB) instead of time-based for predictable indexing
• Monitor Elasticsearch disk usage and configure watermark thresholds
• Set retention to match your storage capacity and compliance requirements
• Use Elasticsearch ILM (Index Lifecycle Management) for advanced rotation
• Use DodaTech's Graylog Storage Planner to model index growth

Common Mistakes with index rotation

1. Overlapping type class instances that cause GHC to reject the program with ambiguous dispatch errors
2. Non-exhaustive pattern matches that compile with warnings then crash at runtime
3. Misunderstanding that String is [Char] with poor performance for large text operations

These mistakes appear frequently in real-world GRAYLOG code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

FAQ

Related: DodaTech's Elasticsearch Performance Guide provides tuning recommendations for Graylog index performance, shard sizing, and cluster health.