add doc for udp routing

content/en/guides/traffic_management/ingress/fsm_gateway/udp_routing.md

@@ -0,0 +1,120 @@
+---
+title: "UDP Routing"
+description: "This document outlines setting up a UDPRoute in Kubernetes to route UDP traffic through an FSM Gateway, using Fortio server as a sample application."
+type: docs
+weight: 19
+draft: false
+---
+
+The [UDPRoute](https://gateway-api.sigs.k8s.io/reference/spec/#gateway.networking.k8s.io/v1alpha2.UDPRoute) provides a method to route UDP traffic. When combined with a gateway listener, it can be used to forward traffic on a port specified by the listener to a set of backends defined in the UDPRoute.
+
+## Prerequisites
+
+- Kubernetes cluster version {{< param min_k8s_version_gateway_api >}} or higher.
+- kubectl CLI
+- FSM Gateway installed via [guide doc](/guides/traffic_management/ingress/fsm_gateway/installation).
+
+## Demonstration
+
+## Prerequisites
+
+- Kubernetes cluster
+- kubectl tool
+
+## Environment Setup
+
+### Deploying Sample Application
+
+Use [fortio server](https://github.com/fortio/fortio) as a sample application, which provides a UDP service listening on port `8078` and echoes back the content sent by the client.
+
+```shell
+kubectl create namespace server
+kubectl apply -n server -f - <<EOF
+apiVersion: v1
+kind: Service
+metadata:
+  name: fortio
+  labels:
+    app: fortio
+    service: fortio
+spec:
+  ports:
+  - port: 8078
+    name: udp-8078
+  selector:
+    app: fortio
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: fortio
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: fortio
+  template:
+    metadata:
+      labels:
+        app: fortio
+    spec:
+      containers:
+      - name: fortio
+        image: fortio/fortio:latest_release
+        imagePullPolicy: Always
+        ports:
+        - containerPort: 8078
+          name: http
+EOF
+```
+
+### Creating UDP Gateway
+
+Next, create a [Gateway](https://gateway-api.sigs.k8s.io/reference/spec/#gateway.networking.k8s.io/v1alpha2.Gateway) for the UDP service, setting the protocol of the listening port to `UDP`.
+
+```shell
+kubectl apply -n server -f - <<EOF
+apiVersion: gateway.networking.k8s.io/v1beta1
+kind: Gateway
+metadata:
+  namespace: server
+  name: simple-fsm-gateway
+spec:
+  gatewayClassName: fsm-gateway-cls
+  listeners:
+    - protocol: UDP
+      port: 8000
+      name: udp
+EOF
+```
+
+### Creating UDP Route
+
+Similar to the HTTP protocol, to access backend services through the gateway, a [UDPRoute](https://gateway-api.sigs.k8s.io/reference/spec/#gateway.networking.k8s.io/v1alpha2.UDPRoute) needs to be created.
+
+```shell
+kubectl -n server apply -f - <<EOF
+apiVersion: gateway.networking.k8s.io/v1alpha2
+kind: UDPRoute
+metadata:
+  name: udp-route-sample
+spec:
+  parentRefs:
+    - name: simple-fsm-gateway
+      namespace: server
+      port: 8000
+  rules:
+  - backendRefs:
+    - name: fortio
+      port: 8078
+EOF
+```
+
+Test accessing the UDP service. After sending the word 'fsm', the same word will be received back.
+
+```shell
+export GATEWAY_IP=$(kubectl get svc -n server -l app=fsm-gateway -o jsonpath='{.items[0].status.loadBalancer.ingress[0].ip}')
+
+echo 'fsm' | nc -4u -w1 $GATEWAY_IP 8000
+fsm
+```