Merge pull request #27092 from XudongLiuHarold/add-service-loadbalancer-class

Add documentation for Service LoadBalancerClass

Author: k8s-ci-robot

content/en/docs/concepts/services-networking/service.md

@@ -633,6 +633,25 @@ is set to `false` on an existing Service with allocated node ports, those node p
 You must explicitly remove the `nodePorts` entry in every Service port to de-allocate those node ports.
 You must enable the `ServiceLBNodePortControl` feature gate to use this field.
 
+#### Specifying class of load balancer implementation {#load-balancer-class}
+
+{{< feature-state for_k8s_version="v1.21" state="alpha" >}}
+
+Starting in v1.21, you can optionally specify the class of a load balancer implementation for
+`LoadBalancer` type of Service by setting the field `spec.loadBalancerClass`.
+By default, `spec.loadBalancerClass` is `nil` and a `LoadBalancer` type of Service uses
+the cloud provider's default load balancer implementation. 
+If `spec.loadBalancerClass` is specified, it is assumed that a load balancer
+implementation that matches the specified class is watching for Services.
+Any default load balancer implementation (for example, the one provided by
+the cloud provider) will ignore Services that have this field set.
+`spec.loadBalancerClass` can be set on a Service of type `LoadBalancer` only.
+Once set, it cannot be changed. 
+The value of `spec.loadBalancerClass` must be a label-style identifier,
+with an optional prefix such as "`internal-vip`" or "`example.com/internal-vip`".
+Unprefixed names are reserved for end-users.
+You must enable the `ServiceLoadBalancerClass` feature gate to use this field.
+
 #### Internal load balancer
 
 In a mixed environment it is sometimes necessary to route traffic from Services inside the same

content/en/docs/reference/command-line-tools-reference/feature-gates.md

@@ -163,6 +163,7 @@ different Kubernetes components.
 | `ServerSideApply` | `false` | Alpha | 1.14 | 1.15 |
 | `ServerSideApply` | `true` | Beta | 1.16 | |
 | `ServiceLBNodePortControl` | `false` | Alpha | 1.20 | |
+| `ServiceLoadBalancerClass` | `false` | Alpha | 1.21 | |
 | `ServiceNodeExclusion` | `false` | Alpha | 1.8 | 1.18 |
 | `ServiceNodeExclusion` | `true` | Beta | 1.19 | |
 | `ServiceTopology` | `false` | Alpha | 1.17 | |
@@ -772,6 +773,7 @@ Each feature gate is designed for enabling/disabling a specific feature:
 - `ServiceAppProtocol`: Enables the `AppProtocol` field on Services and Endpoints.
 - `ServiceLBNodePortControl`: Enables the `spec.allocateLoadBalancerNodePorts`
   field on Services.
+- `ServiceLoadBalancerClass`: Enables the `LoadBalancerClass` field on Services. See [Specifying class of load balancer implementation](/docs/concepts/services-networking/service/#specifying-class-of-load-balancer-implementation-load-balancer-class) for more details.
 - `ServiceLoadBalancerFinalizer`: Enable finalizer protection for Service load balancers.
 - `ServiceNodeExclusion`: Enable the exclusion of nodes from load balancers
   created by a cloud provider. A node is eligible for exclusion if labelled with