add doc about how to specify vip in gateway

Author: woodgear

docs/en/configure/networking/functions/configure_gatewayapi_gateway.mdx

@@ -49,6 +49,16 @@ In YAML, this setting is configured in the companion `EnvoyProxy` resource at
 The advantage is ease of use and high-availability load balancing capabilities.
 To use LoadBalancer, the cluster must have LoadBalancer support, which can be enabled via [MetalLB](./configure_metallb.mdx#configure_ip_pool).
 
+When using MetalLB, you can specify a static VIP through service annotations. In the Web Console, use the **Service Annotation** field:
+
+```yaml
+metallb.universe.tf/address-pool: ADDRESS_POOL_NAME
+# Or specify a specific IP directly
+metallb.universe.tf/loadBalancerIPs: VIP_IP
+```
+
+For more details, see [How To Specify a VIP When Using MetalLB](../how_to/tasks_for_envoy_gateway.mdx#specify_vip_metallb).
+
 #### NodePort \{#access_gateway_via_nodeport}
 
 The advantage is that it doesn't require any external dependencies.

docs/en/configure/networking/how_to/tasks_for_envoy_gateway.mdx

@@ -151,6 +151,46 @@ spec:
 NodePort can only be within a specific range, typically `30000-32767`. If you want the Gateway listener port and NodePort to be consistent, your listener port must also be within the NodePort range.
 :::
 
+### How To Specify a VIP When Using MetalLB \{#specify_vip_metallb}
+
+When using MetalLB as the LoadBalancer provider, you can specify a static VIP for the Gateway service through service annotations.
+
+```yaml
+apiVersion: gateway.envoyproxy.io/v1alpha1
+kind: EnvoyProxy
+metadata:
+  name: demo
+  namespace: demo
+spec:
+  provider:
+    type: Kubernetes
+    kubernetes:
+      envoyService:
+        type: LoadBalancer
+        annotations:                                      # [!code callout]
+          metallb.universe.tf/address-pool: production    # [!code callout]
+          metallb.universe.tf/loadBalancerIPs: VIP_IP   # [!code callout]
+```
+
+<Callouts>
+  1. Add MetalLB annotations in the `envoyService.annotations` field
+  2. Specify the address pool name to allocate IP from
+  3. Or specify a specific IP address (must be within the address pool range)
+</Callouts>
+
+**Available Annotations:**
+
+| Annotation | Description |
+| ---------- | ----------- |
+| `metallb.universe.tf/address-pool` | Select the address pool to allocate IP from |
+| `metallb.universe.tf/loadBalancerIPs` | Specify a specific IP address (supports multiple IPs, comma-separated) |
+
+:::note
+- The specified IP must be within a configured MetalLB address pool
+- Make sure MetalLB is properly installed and configured before specifying VIPs
+- For MetalLB configuration, see [Configure MetalLB](../functions/configure_metallb.mdx#configure_ip_pool)
+:::
+
 ### How To Add Pod Annotations In Envoy Gateway
 
 [Add pod annotation](./configure_endpoint_health_checker.mdx#add_pod_annotation_in_envoy_gateway)
@@ -363,8 +403,8 @@ For applications running inside the cluster, use the service ClusterIP instead o
 If you need to access the LoadBalancer VIP from any cluster node, change `externalTrafficPolicy` to `Cluster`:
 
 ```bash
-kubectl patch envoyproxy $GATEWAY_NAME -n $GATEWAY_NS --type='json' -p='[  
-  {"op": "replace", "path": "/spec/provider/kubernetes/envoyService/externalTrafficPolicy", "value": "Cluster"}  
+kubectl patch envoyproxy $GATEWAY_NAME -n $GATEWAY_NS --type='json' -p='[
+  {"op": "replace", "path": "/spec/provider/kubernetes/envoyService/externalTrafficPolicy", "value": "Cluster"}
 ]'
 ```