Load Balancer Tester

Overview

Validate load balancer behavior including traffic distribution algorithms, health check mechanisms, failover scenarios, session persistence, and SSL termination. Supports testing for NGINX, HAProxy, AWS ALB/NLB, GCP Load Balancers, and Kubernetes Ingress controllers.

Prerequisites

• Load balancer deployed and accessible in a test environment
• Multiple backend instances running with identifiable responses (hostname headers)
• HTTP client tools (curl, wrk, hey, or k6) for sending test traffic
• Access to load balancer configuration and health check settings
• Ability to stop/start backend instances to simulate failures

Instructions

1. Verify basic load balancer connectivity:

• Send a request through the load balancer and confirm a backend response.
• Check the response includes identifying headers (X-Backend-Server, Server) to determine which instance served the request.
• Verify SSL/TLS termination works correctly (valid certificate, proper redirect from HTTP to HTTPS).

1. Test traffic distribution algorithm:

• Send 100+ sequential requests and record which backend handled each.
• For round-robin: verify even distribution across all backends (within 5% tolerance).
• For least-connections: verify the least-loaded backend receives new requests.
• For weighted: verify traffic ratio matches configured weights.

1. Validate health check behavior:

• Stop one backend instance.
• Verify the load balancer detects the failure within the configured health check interval.
• Confirm subsequent requests are routed only to healthy backends (zero errors).
• Restart the backend and verify it is returned to the pool after passing health checks.

1. Test failover scenarios:

• Stop all backends except one and verify the remaining backend handles all traffic.
• Stop all backends and verify the load balancer returns a 502 or 503 error (not hang).
• Simulate slow backend responses and verify timeout behavior.

1. Validate session persistence (sticky sessions):

• Send multiple requests with the same session cookie.
• Verify all requests route to the same backend instance.
• Verify a new session (no cookie) can route to any backend.

1. Test connection draining:

• Start a long-running request, then remove the backend from the pool.
• Verify the in-flight request completes successfully.
• Verify new requests route to remaining backends.

1. Document all results with request/response evidence and timing data.

Output

• Traffic distribution report show