Thanos sidecar: Prometheus not reachable

What is Thanos sidecar: Prometheus not reachable

Understanding Thanos and Its Purpose

Thanos is an open-source project that provides highly available Prometheus setup with long-term storage capabilities. It is designed to scale out Prometheus by enabling global query view, unlimited storage, and high availability. Thanos Sidecar is a crucial component that runs alongside Prometheus, allowing it to connect with the rest of the Thanos components.

Identifying the Symptom: Prometheus Not Reachable

When using Thanos, you might encounter an issue where the Sidecar reports that Prometheus is not reachable. This symptom typically manifests as error logs indicating connection failures or timeouts when the Sidecar attempts to communicate with Prometheus.

Common Error Messages

"Error: Prometheus not reachable" "Connection refused" "Timeout while connecting to Prometheus"

Exploring the Issue: Root Causes

The primary reason for this issue is that the Thanos Sidecar cannot establish a connection with the Prometheus instance. This can be due to several factors, including:

Network connectivity issues between the Sidecar and Prometheus. Incorrect configuration of the Prometheus URL in the Sidecar settings. Firewall rules blocking the connection.

Configuration Check

Ensure that the configuration file for the Sidecar has the correct Prometheus URL. This is typically set in the --prometheus.url flag when starting the Sidecar.

Steps to Resolve the Issue

To resolve the issue of the Sidecar not being able to reach Prometheus, follow these steps:

Step 1: Verify Network Connectivity

Ensure that the network allows communication between the Sidecar and Prometheus. You can test this by using curl or ping commands:

ping <prometheus-host>curl http://<prometheus-host>:<prometheus-port>/metrics

Step 2: Check Prometheus URL Configuration

Open the configuration file or check the startup command for the Sidecar to ensure the Prometheus URL is correctly specified:

--prometheus.url=http://<prometheus-host>:<prometheus-port>

Step 3: Review Firewall and Security Groups

Ensure that any firewalls or security groups allow traffic on the Prometheus port. Adjust the rules if necessary to permit communication.

Step 4: Restart Services

After making changes, restart both the Prometheus and Thanos Sidecar services to apply the new configurations:

systemctl restart prometheussystemctl restart thanos-sidecar

Additional Resources

For more detailed information, you can refer to the official Thanos Sidecar documentation and the Prometheus Overview.