Thanos compaction: failed to delete old blocks

What is Thanos compaction: failed to delete old blocks

Understanding Thanos and Its Purpose

Thanos is a highly scalable, multi-cluster monitoring system that builds upon Prometheus. It is designed to provide long-term storage, global querying, and high availability for Prometheus metrics. By using object storage, Thanos allows users to store historical data efficiently and query it across multiple Prometheus instances.

Identifying the Symptom

When using Thanos, you might encounter an error during the compaction process: compaction: failed to delete old blocks. This error indicates that Thanos is unable to remove outdated data blocks from the object storage, which can lead to increased storage costs and potential performance issues.

Exploring the Issue

The error compaction: failed to delete old blocks typically arises due to insufficient permissions on the object storage. Thanos requires the ability to delete old blocks to manage storage efficiently. If the necessary permissions are not granted, Thanos cannot perform this task, resulting in the error.

Common Causes

Incorrect IAM policies or roles assigned to Thanos. Misconfigured access control lists (ACLs) on the object storage. Network issues preventing Thanos from reaching the storage backend.

Steps to Fix the Issue

To resolve this issue, follow these steps to ensure Thanos has the necessary permissions to delete old blocks:

Step 1: Verify IAM Policies

Ensure that the IAM policies associated with Thanos have the necessary permissions to delete objects in the storage bucket. For example, if you are using AWS S3, the policy should include the s3:DeleteObject permission.

{ "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": "s3:DeleteObject", "Resource": "arn:aws:s3:::your-bucket-name/*" } ]}

Step 2: Check Access Control Lists (ACLs)

Review the ACLs on your object storage to ensure that Thanos has the necessary permissions. Adjust the ACLs if needed to grant delete permissions.

Step 3: Test Connectivity

Ensure that Thanos can reach the object storage backend without any network issues. You can test this by attempting to list or delete a test object using a tool like AWS CLI or gsutil.

Conclusion

By ensuring that Thanos has the correct permissions and network access to your object storage, you can resolve the compaction: failed to delete old blocks error. This will help maintain efficient storage management and prevent unnecessary costs. For more information on configuring Thanos, visit the official Thanos documentation.