docs: multiple routes (#47)

Signed-off-by: Kostis Kapelonis <[email protected]>

docs/features/multiple-routes.md

@@ -1,7 +1,111 @@
 # Using Multiple Routes
 
-!!! warning
-    Page under construction.
-
+The Gateway plugin can control more than one HTTP routes during a canary.
+This is a very common scenario if you have micro-services and the same application can be accessed by different routes.
 
-To be written
+
+![multiple routes](../images/multiple-routes/multiple-routes.png)
+
+As an  example you have application A that uses application C at `backend.example.com` while application B also depends on C but this time as `api.example.com`
+
+You want to perform a canary deployment for application C so it is crucial that during the canary both HTTP routes change weights.
+
+First you define the two HTTP routes
+
+```yaml
+---
+kind: HTTPRoute
+apiVersion: gateway.networking.k8s.io/v1beta1
+metadata:
+  name: backend-route
+  namespace: default
+spec:
+  parentRefs:
+    - name: eg
+  hostnames:
+    - backend.example.com  
+  rules:
+  - matches:
+    - path:
+        type: PathPrefix
+        value: /
+    backendRefs:
+    - name: argo-rollouts-stable-service
+      kind: Service
+      port: 80
+    - name: argo-rollouts-canary-service
+      kind: Service
+      port: 80
+---
+kind: HTTPRoute
+apiVersion: gateway.networking.k8s.io/v1beta1
+metadata:
+  name: api-route
+  namespace: default
+spec:
+  parentRefs:
+    - name: eg
+  hostnames:
+    - api.example.com     
+  rules:
+  - matches:
+    - path:
+        type: PathPrefix
+        value: /
+    backendRefs:
+    - name: argo-rollouts-stable-service
+      kind: Service
+      port: 80
+    - name: argo-rollouts-canary-service
+      kind: Service
+      port: 80
+```
+
+Then in your Rollout definition you use the `httproutes` property that
+accepts a list of routes to be controlled.
+
+```yaml
+apiVersion: argoproj.io/v1alpha1
+kind: Rollout
+metadata:
+  name: rollouts-demo
+  namespace: default
+spec:
+  replicas: 5
+  strategy:
+    canary:
+      canaryService: argo-rollouts-canary-service
+      stableService: argo-rollouts-stable-service
+      trafficRouting:
+        plugins:
+          argoproj-labs/gatewayAPI:
+            httpRoutes:
+              - name: backend-route
+              - name: api-route
+            namespace: default
+      steps:
+      - setWeight: 10
+      - pause: {}
+      - setWeight: 50
+      - pause: {}
+      - setWeight: 100
+      - pause: {}
+  revisionHistoryLimit: 2
+  selector:
+    matchLabels:
+      app: rollouts-demo
+  template:
+    metadata:
+      labels:
+        app: rollouts-demo
+    spec:
+      containers:
+        - name: rollouts-demo
+          image: <my-image:my-tag>
+          ports:
+            - name: http
+              containerPort: 8080
+              protocol: TCP
+```              
+
+If you now start a canary deployment both routes will change to 10%, 50% and 100% as the canary progresses to all its steps.