add a local tlsTransportCache to available_controller

The available_controller creates short-lived clients to sync remote APIService
objects. These clients are constructed with HTTP transports that cannot
be cached by client-go (because client-go won't know whether the TLS configs
have dynamic functions or not), which may spam idle connections. A local
cache works because we know all the configs share the same dialer
function, and can only vary on the dynamic cert/key.

staging/src/k8s.io/kube-aggregator/pkg/controllers/status/available_controller.go

@@ -86,6 +86,53 @@ type AvailableConditionController struct {
 	cache map[string]map[string][]string
 	// this lock protects operations on the above cache
 	cacheLock sync.RWMutex
+
+	// TLS config with customized dialer cannot be cached by the client-go
+	// tlsTransportCache. Use a local cache here to reduce the chance of
+	// the controller spamming idle connections with short-lived transports.
+	// NOTE: the cache works because we assume that the transports constructed
+	// by the controller only vary on the dynamic cert/key.
+	tlsCache *tlsTransportCache
+}
+
+type tlsTransportCache struct {
+	mu         sync.Mutex
+	transports map[tlsCacheKey]http.RoundTripper
+}
+
+func (c *tlsTransportCache) get(config *rest.Config) (http.RoundTripper, error) {
+	// If the available controller doesn't customzie the dialer (and we know from
+	// the code that the controller doesn't customzie other functions i.e. Proxy
+	// and GetCert (ExecProvider)), the config is cacheable by the client-go TLS
+	// transport cache. Let's skip the local cache and depend on the client-go cache.
+	if config.Dial == nil {
+		return rest.TransportFor(config)
+	}
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	// See if we already have a custom transport for this config
+	key := tlsConfigKey(config)
+	if t, ok := c.transports[key]; ok {
+		return t, nil
+	}
+	restTransport, err := rest.TransportFor(config)
+	if err != nil {
+		return nil, err
+	}
+	c.transports[key] = restTransport
+	return restTransport, nil
+}
+
+type tlsCacheKey struct {
+	certData string
+	keyData  string
+}
+
+func tlsConfigKey(c *rest.Config) tlsCacheKey {
+	return tlsCacheKey{
+		certData: string(c.TLSClientConfig.CertData),
+		keyData:  string(c.TLSClientConfig.KeyData),
+	}
 }
 
 // NewAvailableConditionController returns a new AvailableConditionController.
@@ -115,6 +162,7 @@ func NewAvailableConditionController(
 			workqueue.NewItemExponentialFailureRateLimiter(5*time.Millisecond, 30*time.Second),
 			"AvailableConditionController"),
 		proxyCurrentCertKeyContent: proxyCurrentCertKeyContent,
+		tlsCache:                   &tlsTransportCache{transports: make(map[tlsCacheKey]http.RoundTripper)},
 	}
 
 	if egressSelector != nil {
@@ -185,7 +233,12 @@ func (c *AvailableConditionController) sync(key string) error {
 	if c.dialContext != nil {
 		restConfig.Dial = c.dialContext
 	}
-	restTransport, err := rest.TransportFor(restConfig)
+	// TLS config with customized dialer cannot be cached by the client-go
+	// tlsTransportCache. Use a local cache here to reduce the chance of
+	// the controller spamming idle connections with short-lived transports.
+	// NOTE: the cache works because we assume that the transports constructed
+	// by the controller only vary on the dynamic cert/key.
+	restTransport, err := c.tlsCache.get(restConfig)
 	if err != nil {
 		return err
 	}

staging/src/k8s.io/kube-aggregator/pkg/controllers/status/available_controller_test.go

@@ -18,6 +18,7 @@ package apiserver
 
 import (
 	"fmt"
+	"net"
 	"net/http"
 	"net/http/httptest"
 	"net/url"
@@ -133,6 +134,7 @@ func setupAPIServices(apiServices []*apiregistration.APIService) (*AvailableCond
 			// the maximum disruption time to a minimum, but it does prevent hot loops.
 			workqueue.NewItemExponentialFailureRateLimiter(5*time.Millisecond, 30*time.Second),
 			"AvailableConditionController"),
+		tlsCache: &tlsTransportCache{transports: make(map[tlsCacheKey]http.RoundTripper)},
 	}
 	for _, svc := range apiServices {
 		c.addAPIService(svc)
@@ -202,6 +204,55 @@ func TestBuildCache(t *testing.T) {
 		})
 	}
 }
+
+func TestTLSCache(t *testing.T) {
+	apiServices := []*apiregistration.APIService{newRemoteAPIService("remote.group")}
+	services := []*v1.Service{newService("foo", "bar", testServicePort, testServicePortName)}
+	c, _ := setupAPIServices(apiServices)
+	// TLS configs with customized dialers are uncacheable by the client-go
+	// TLS transport cache. The local cache will be used.
+	c.dialContext = (&net.Dialer{
+		Timeout:   30 * time.Second,
+		KeepAlive: 30 * time.Second,
+	}).DialContext
+	for _, svc := range services {
+		c.addService(svc)
+	}
+	tests := []struct {
+		name                       string
+		proxyCurrentCertKeyContent certKeyFunc
+		expectedCacheSize          int
+	}{
+		{
+			name:              "nil certKeyFunc",
+			expectedCacheSize: 1,
+		},
+		{
+			name:                       "empty certKeyFunc",
+			proxyCurrentCertKeyContent: func() ([]byte, []byte) { return emptyCert(), emptyCert() },
+			// the tlsCacheKey is the same, reuse existing transport
+			expectedCacheSize: 1,
+		},
+		{
+			name:                       "different certKeyFunc",
+			proxyCurrentCertKeyContent: testCertKeyFunc,
+			// the tlsCacheKey is different, create a new transport
+			expectedCacheSize: 2,
+		},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			c.proxyCurrentCertKeyContent = tc.proxyCurrentCertKeyContent
+			for _, apiService := range apiServices {
+				c.sync(apiService.Name)
+			}
+			if len(c.tlsCache.transports) != tc.expectedCacheSize {
+				t.Fatalf("%v cache size expected %v, got %v", tc.name, tc.expectedCacheSize, len(c.tlsCache.transports))
+			}
+		})
+	}
+}
+
 func TestSync(t *testing.T) {
 	tests := []struct {
 		name string
@@ -356,6 +407,7 @@ func TestSync(t *testing.T) {
 				endpointsLister:            v1listers.NewEndpointsLister(endpointsIndexer),
 				serviceResolver:            &fakeServiceResolver{url: testServer.URL},
 				proxyCurrentCertKeyContent: func() ([]byte, []byte) { return emptyCert(), emptyCert() },
+				tlsCache:                   &tlsTransportCache{transports: make(map[tlsCacheKey]http.RoundTripper)},
 			}
 			c.sync(tc.apiServiceName)
 
@@ -420,3 +472,33 @@ func TestUpdateAPIServiceStatus(t *testing.T) {
 func emptyCert() []byte {
 	return []byte{}
 }
+
+func testCertKeyFunc() ([]byte, []byte) {
+	return []byte(`-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----`), []byte(`-----BEGIN RSA PRIVATE KEY-----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+-----END RSA PRIVATE KEY-----`)
+}