🚀 Migrating from Ingress to Gateway API with Conditional Routing¶

📌 The Question¶

The task is to migrate an existing Ingress configuration to a Gateway API HTTPRoute. The old Ingress file is located at /opt/course/13/ingress.yaml.

Key requirements:

Work in Namespace project-r500.
Use the already existing Gateway (reachable at http://r500.gateway:30080).
Create a new HTTPRoute named traffic-director.
The HTTPRoute must replicate the old Ingress routes:
/desktop → forwards to service web-desktop
/mobile → forwards to service web-mobile
Extend the HTTPRoute with a new rule for /auto:
If User-Agent header is exactly mobile → forward to web-mobile
Otherwise (any other header or no header at all) → forward to web-desktop

📌 The Old Ingress¶

Here’s the original Ingress manifest we are migrating:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: traffic-director
spec:
  ingressClassName: nginx
  rules:
    - host: r500.gateway
      http:
        paths:
          - backend:
              service:
                name: web-desktop
                port:
                  number: 80
            path: /desktop
            pathType: Prefix
          - backend:
              service:
                name: web-mobile
                port:
                  number: 80
            path: /mobile
            pathType: Prefix

👉 This simply maps /desktop → web-desktop and /mobile → web-mobile.

📌 Migrating to Gateway API¶

Gateway API is the next-generation alternative to Ingress.

Instead of defining rules in Ingress, we use HTTPRoute.
HTTPRoute attaches to an existing Gateway via parentRefs.
We can match traffic based on hostname, path, headers, and more.

📌 The New HTTPRoute (With Deep Comments)¶

apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: traffic-director                # Same name for clarity
  namespace: project-r500               # Always set the correct namespace
spec:
  parentRefs:
    - name: main                        # Attach to the existing Gateway
      namespace: project-r500
  hostnames:
    - r500.gateway                      # Same hostname as in old Ingress

  rules:
    # -------------------------------
    # Rule 1: /desktop → web-desktop
    # -------------------------------
    - matches:
        - path:
            type: PathPrefix            # PathPrefix = matches /desktop and subpaths
            value: /desktop
      backendRefs:
        - name: web-desktop             # Service name
          port: 80                      # Service port

    # -------------------------------
    # Rule 2: /mobile → web-mobile
    # -------------------------------
    - matches:
        - path:
            type: PathPrefix
            value: /mobile
      backendRefs:
        - name: web-mobile
          port: 80

    # -------------------------------
    # Rule 3a: /auto + User-Agent: mobile → web-mobile
    # -------------------------------
    - matches:
        - path:
            type: PathPrefix
            value: /auto
          headers:                      # Match HTTP header conditions
            - type: Exact               # "Exact" = must match exactly
              name: User-Agent          # The header we are checking
              value: mobile             # Match only if User-Agent = "mobile"
      backendRefs:
        - name: web-mobile
          port: 80

    # -------------------------------
    # Rule 3b: /auto (fallback) → web-desktop
    # -------------------------------
    - matches:
        - path:
            type: PathPrefix
            value: /auto
          # Note: no header match here → this acts as a fallback rule
      backendRefs:
        - name: web-desktop
          port: 80

📌 How the `/auto` Rule Works¶

Two separate rules are required:
Specific case: /auto + User-Agent: mobile → web-mobile
General case: /auto (no header or any other header) → web-desktop
Gateway API processes rules in order:
If the header matches mobile, the first rule wins.
If not, the fallback rule applies.

📌 Testing the Setup¶

After applying the manifest:

# Desktop route
curl r500.gateway:30080/desktop

# Mobile route
curl r500.gateway:30080/mobile

# Auto route with User-Agent: mobile
curl r500.gateway:30080/auto -H "User-Agent: mobile"

# Auto route with no header (falls back to desktop)
curl r500.gateway:30080/auto

✅ Expected Results:

/desktop → response from web-desktop
/mobile → response from web-mobile
/auto with User-Agent: mobile → response from web-mobile
/auto without header (or any non-mobile header) → response from web-desktop

📌 Key Takeaways¶

Ingress → Gateway API migration = mostly about moving path-based rules into HTTPRoute.
Gateway API provides much finer control, especially with header-based routing.
The /auto path demonstrates conditional routing: same path but different backend depending on request headers.
Always define a fallback rule when doing conditional routing.