Executing A/B Testing Using Header-Based Routing

In this lesson, you will learn how to route specific user segments to different versions of your application by inspecting HTTP headers within your Ingress controller.

Why Header-Based Routing?

While canary releases often use weight-based splitting to send a percentage of total traffic to a new version, A/B testing requires more precision. You want to ensure that specific users—such as internal testers, beta program participants, or users from a specific region—consistently see a new feature, regardless of the overall traffic distribution. By inspecting an HTTP header (like x-version: beta), you can force traffic to a specific Service version.

Implementing the Strategy

Most modern Ingress controllers, such as NGINX, allow you to define custom routing rules based on header matching. Instead of a single destination for your host, you define multiple rules that prioritize specific request characteristics.

Consider an scenario where you have a stable v1 app and a new v2 app. You can configure your Ingress resource to prioritize traffic carrying a specific header:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: ab-testing-ingress
  annotations:
    nginx.ingress.kubernetes.io/canary: "true"
    nginx.ingress.kubernetes.io/canary-by-header: "x-user-segment"
    nginx.ingress.kubernetes.io/canary-by-header-value: "beta"
spec:
  rules:
  - host: myapp.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: myapp-v2
            port:
              number: 80

How It Works

1. The Header Match: When an incoming request hits the Ingress, the controller inspects the x-user-segment header.
2. Conditional Routing: If the value matches beta, the Ingress controller bypasses the standard routing logic and sends the request directly to the myapp-v2 backend service.
3. Graceful Fallback: If the header is missing or contains a different value, the Ingress ignores this rule and routes the request to your production stable v1 backend as usual.

This approach gives you total control over the testing environment, ensuring that your experiments do not interfere with the experience of the general user base.

Key Takeaway: Header-based routing allows you to isolate specific user segments for A/B testing by using Ingress annotations to force traffic to target service versions based on request metadata.