Add interopt test using xDS client for a random_subsetting_experiment

[marek-szews]

Enable interop testing for random subsetting Load Balancing policy (experimantal) to validate correctness and integration with existing child policies.

RELEASE NOTES:

Add interop test for a random_subsetting_experimental LB policy.

[Pranjali-2501]

@marek-szews : please merge changes from the master branch into this PR branch. Thanks.

[arjan-bal]

Please add the following test cases to validate xDS integration:

1. Configuration parsing test here
   

   grpc-go/internal/xds/xdsclient/xdslbregistry/xdslbregistry_test.go

   Line 74 in 2de5b1c

   func (s) TestConvertToServiceConfigSuccess(t *testing.T) {

2. A test that configures random subsetting using xDS and verifies that the balancer is built and RPCs succeed. You can look at the following test that configures pickfirst:
   

   grpc-go/internal/xds/balancer/clustermanager/e2e_test/clustermanager_test.go

   Lines 198 to 222 in 2de5b1c

   	// Create a wrapped pickfirst LB policy. When the endpoint picking policy on
   	// the cluster resource is changed to pickfirst, this will allow us to
   	// verify that load balancing configuration is pushed to it.
   	pfBuilder := balancer.Get(pickfirst.Name)
   	internal.BalancerUnregister(pfBuilder.Name())
   	lbCfgCh := make(chan serviceconfig.LoadBalancingConfig, 1)
   	stub.Register(pfBuilder.Name(), stub.BalancerFuncs{
   	ParseConfig: func(lbCfg json.RawMessage) (serviceconfig.LoadBalancingConfig, error) {
   	return pfBuilder.(balancer.ConfigParser).ParseConfig(lbCfg)
   	},
   	Init: func(bd *stub.BalancerData) {
   	bd.ChildBalancer = pfBuilder.Build(bd.ClientConn, bd.BuildOptions)
   	},
   	UpdateClientConnState: func(bd *stub.BalancerData, ccs balancer.ClientConnState) error {
   	select {
   	case lbCfgCh <- ccs.BalancerConfig:
   	default:
   	}
   	return bd.ChildBalancer.UpdateClientConnState(ccs)
   	},
   	Close: func(bd *stub.BalancerData) {
   	bd.ChildBalancer.Close()
   	},
   	})

[arjan-bal]

The github.com/envoyproxy/go-control-plane/envoy dependency is already updated on the master branch. Can you please merge the master branch to remove this diff?

[arjan-bal]

"least_request_lb_config" - this seems like a copy/paste error. Can you please fix the comment?

[arjan-bal]

I quickly glanced through A68 and didn't find any mention of a defaultRandomSubsetSize. Is this behavior documented? If not, we should probably fail parsing if the subset size is less than 1.

[arjan-bal]

This doesn't appear to be an xDS or an interop test. It is a simple unit test that directly configures the LB policy through a static service config, instead of using xDS. Please remove this. Let's keep this PR focused on integrating the random subsetting policy with xDS and have the interop changes in separate PRs.

[easwars]

@marek-szews
Did we implement parsing the random_subsetting LB policy's configuration from xDS protos? I don't remember us doing that at all. We need to register a custom policy in the xDS LB registry that can parse the xDS protos to arrive at the LB config. I'm talking about this section in A68: https://github.com/grpc/proposal/blob/master/A68-random-subsetting.md#integration-with-xds-lb-policy-registry

[github-actions]

This PR is labeled as requiring an update from the reporter, and no update has been received after 6 days. If no update is provided in the next 7 days, this issue will be automatically closed.