Loki Index Gateway Error — Quick Fix

In this tutorial, you'll learn about Loki Index Gateway Error. We cover key concepts, practical examples, and best practices.

The Problem

Loki queries are failing or returning incomplete results due to index gateway issues. The index gateway may be unable to read the index, or the boltb-shipper index may be corrupted. Query performance may degrade significantly.

Error example:

index-gateway: failed to query index: boltdb: file corruption detected
index-gateway: no index found for period 2026-06-24
index-gateway: query frontend timeout waiting for index gateway response

The Fix

Step 1: Check index gateway health

WRONG — assuming the query frontend is the problem:

# Query issues often originate in the index gateway

RIGHT — check index gateway status:

# Check index gateway readiness
curl http://loki-index-gateway:3100/ready

# Check for index files
kubectl exec -n loki loki-index-gateway-0 -- ls -la /data/loki/index/

Output:

total 12345
drwxr-xr-x 2 root root 4096 Jun 24 10:00 .
-rw-r--r-- 1 root root 10485760 Jun 24 10:00 index_12345.gz

Step 2: Rebuild corrupted index files

WRONG — manually deleting index files:

# Deleting index files causes permanent data loss for querying

RIGHT — re-ship the index:

# Trigger re-shipping of index from ingesters
# This is done by scaling the index gateway down and up
kubectl scale statefulset loki-index-gateway --replicas=0 -n loki
kubectl scale statefulset loki-index-gateway --replicas=2 -n loki

# Or use the boltdb-shipper compaction to rebuild
# In Loki config:
storage:
  boltdb_shipper:
    active_index_directory: /data/loki/index
    cache_location: /data/loki/cache
    resync_interval: 5m

Use DodaTech's Index Health Monitor to track index gateway performance, cache hit rates, and boltdb file integrity.

Prevention Tips

• Use dedicated persistent volumes for index storage (SSD recommended)
• Set boltdb-shipper cache_location with sufficient space (10+ GB)
• Monitor loki_index_gateway_lookup_cache_hit_ratio metric
• Configure index gateway with appropriate memory allocation (4 GB+)
• Use DodaTech's Loki Query Performance Dashboard for index-related bottleneck detection

Common Mistakes with index gateway

1. Using return to exit a function early instead of wrapping a pure value in the monad
2. Mixing let bindings with <- bindings in do notation, producing type errors
3. Overlapping type class instances that cause GHC to reject the program with ambiguous dispatch errors

These mistakes appear frequently in real-world LOKI 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 Loki Troubleshooting Guide covers index gateway health, boltdb maintenance, and query performance optimization for production Loki deployments.