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VMs / EC2 High HTTP 4xx Error Rate

The web server is returning a high number of 4xx errors.

Diagnosing and Resolving High HTTP 4xx Error Rate in VMs / EC2

Understanding Prometheus and Its Purpose

Prometheus is an open-source systems monitoring and alerting toolkit, widely used for monitoring cloud environments like VMs and EC2 instances. It collects metrics from configured targets at given intervals, evaluates rule expressions, displays the results, and triggers alerts if certain conditions are met. Prometheus is particularly useful for identifying performance bottlenecks and ensuring the reliability of your applications.

Symptom: High HTTP 4xx Error Rate

The alert "High HTTP 4xx Error Rate" indicates that your web server is returning a significant number of 4xx status codes. These codes represent client-side errors, such as "404 Not Found" or "403 Forbidden". A persistent high rate of these errors can affect user experience and indicate potential issues with client requests or server configurations.

Details About the Alert

HTTP 4xx errors are client-side errors, meaning the request sent by the client was incorrect or cannot be fulfilled by the server. Common causes include incorrect URLs, unauthorized access attempts, or malformed requests. Monitoring these errors is crucial as they can help identify issues with how clients interact with your application, potentially pointing to broken links, incorrect API usage, or security misconfigurations.

Common 4xx Errors

  • 400 Bad Request: The server cannot process the request due to client error.
  • 401 Unauthorized: Authentication is required and has failed or has not been provided.
  • 403 Forbidden: The request was valid, but the server is refusing action.
  • 404 Not Found: The requested resource could not be found.

Steps to Fix the Alert

To resolve a high HTTP 4xx error rate, follow these steps:

1. Analyze the Logs

Start by examining the server logs to identify patterns or specific endpoints that are generating the most 4xx errors. You can use tools like Logstash or Fluentd to aggregate and analyze logs efficiently.

sudo tail -f /var/log/nginx/access.log

2. Review Client Requests

Check if the client requests are correctly formatted and targeting the right endpoints. Ensure that any API calls are using the correct HTTP methods (GET, POST, etc.) and that the request payloads are valid.

3. Validate Server Configuration

Ensure that your server configuration is correct. Check for any misconfigurations in your web server settings (e.g., Nginx, Apache) that might be causing these errors. Verify that all necessary authentication and authorization mechanisms are properly set up.

sudo nginx -t

4. Implement Error Handling

Implement proper error handling on the client-side to manage and retry failed requests where applicable. This can help reduce the number of erroneous requests reaching the server.

Additional Resources

By following these steps, you can effectively diagnose and resolve high HTTP 4xx error rates, ensuring a smoother experience for your users and maintaining the reliability of your application.

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