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Pod Stuck in CrashLoopBackOff
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Load Balancers LoadBalancer4xxErrorRate

The load balancer is returning a high rate of 4xx errors, indicating client-side issues.

Understanding Load Balancers

Load balancers are crucial components in modern web infrastructure, designed to distribute incoming network traffic across multiple servers. This ensures no single server becomes overwhelmed, enhancing application availability and reliability. Load balancers can operate at various layers of the OSI model, including Layer 4 (transport) and Layer 7 (application).

Symptom: LoadBalancer4xxErrorRate

The LoadBalancer4xxErrorRate alert in Prometheus indicates that the load balancer is experiencing a high rate of 4xx HTTP status codes. These errors typically signify client-side issues, such as malformed requests or unauthorized access attempts.

Details About the Alert

When a load balancer returns a 4xx error, it means the request from the client could not be processed due to client-side errors. Common 4xx errors include:

  • 400 Bad Request: The server cannot process the request due to a client error (e.g., malformed request syntax).
  • 401 Unauthorized: The request requires user authentication.
  • 403 Forbidden: The server understands the request but refuses to authorize it.
  • 404 Not Found: The server cannot find the requested resource.

Monitoring these errors is crucial as they can affect user experience and indicate potential issues with client applications or API usage.

Steps to Fix the Alert

1. Review Client Requests

Start by analyzing the client requests that are causing the 4xx errors. Check the logs of your load balancer or use monitoring tools to identify patterns or specific requests leading to errors. Ensure that clients are sending requests that conform to the expected API specifications.

2. Validate API Documentation

Ensure that your API documentation is up-to-date and accurately reflects the current API endpoints and expected request formats. This will help clients send valid requests. Consider providing examples of valid requests and responses in your documentation.

3. Implement Request Validation

Implement server-side validation to catch malformed requests early. Use middleware or validation libraries to ensure that incoming requests meet the expected criteria before processing them further.

4. Monitor and Adjust Rate Limits

If applicable, review and adjust any rate limiting configurations on your load balancer. Ensure that legitimate traffic is not being inadvertently blocked or throttled, leading to 4xx errors.

Additional Resources

For more information on HTTP status codes, visit the MDN Web Docs on HTTP Status Codes. To learn more about load balancing strategies, check out NGINX's Load Balancing Guide.

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