Merge pull request #44742 from cheftako/aggregate

Automatic merge from submit-queue (batch tested with PRs 46302, 44597, 44742, 46554)

Change to aggregator so it calls a user apiservice via its pod IP.

proxy_handler now does a sideways call to lookup the pod IPs for aservice.
It will then pick a random pod IP to forward the use apiserver request to.

**What this PR does / why we need it**: It allows the aggregator to work without setting up the full network stack on the kube master (i.e. with kube-dns or kube-proxy)

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #44619

**Special notes for your reviewer**:

**Release note**:

```release-note
```

cmd/kube-apiserver/app/aggregator.go

@@ -79,11 +79,13 @@ func createAggregatorConfig(kubeAPIServerConfig genericapiserver.Config, command
 			return nil, err
 		}
 	}
+
 	aggregatorConfig := &aggregatorapiserver.Config{
-		GenericConfig:       &genericConfig,
-		CoreAPIServerClient: client,
-		ProxyClientCert:     certBytes,
-		ProxyClientKey:      keyBytes,
+		GenericConfig:           &genericConfig,
+		CoreAPIServerClient:     client,
+		ProxyClientCert:         certBytes,
+		ProxyClientKey:          keyBytes,
+		EnableAggregatorRouting: commandOptions.EnableAggregatorRouting,
 	}
 
 	return aggregatorConfig, nil

cmd/kube-apiserver/app/options/options.go

@@ -68,6 +68,8 @@ type ServerRunOptions struct {
 
 	ProxyClientCertFile string
 	ProxyClientKeyFile  string
+
+	EnableAggregatorRouting bool
 }
 
 // NewServerRunOptions creates a new ServerRunOptions object with default parameters
@@ -217,4 +219,7 @@ func (s *ServerRunOptions) AddFlags(fs *pflag.FlagSet) {
 	fs.StringVar(&s.ProxyClientKeyFile, "proxy-client-key-file", s.ProxyClientKeyFile,
 		"client certificate key used to prove the identity of the aggragator or kube-apiserver when it proxies requests to a user api-server")
 
+	fs.BoolVar(&s.EnableAggregatorRouting, "enable-aggregator-routing", s.EnableAggregatorRouting,
+		"Turns on aggregator routing requests to endoints IP rather than cluster IP.")
+
 }