UPSTREAM: <carry>: send Retry-After when not ready with a caller opt in

UPSTREAM: <carry>: change opt-in due to upstream revert

OpenShift-Rebase-Source: cd08005

staging/src/k8s.io/apiserver/pkg/server/config.go

@@ -1119,6 +1119,7 @@ func DefaultBuildHandlerChain(apiHandler http.Handler, c *Config) http.Handler {
 	if c.ShutdownSendRetryAfter {
 		handler = genericfilters.WithRetryAfter(handler, c.lifecycleSignals.NotAcceptingNewRequest.Signaled())
 	}
+	handler = genericfilters.WithOptInRetryAfter(handler, c.newServerFullyInitializedFunc())
 	handler = genericfilters.WithHTTPLogging(handler, c.newIsTerminatingFunc())
 	if utilfeature.DefaultFeatureGate.Enabled(genericfeatures.APIServerTracing) {
 		handler = genericapifilters.WithTracing(handler, c.TracerProvider)

staging/src/k8s.io/apiserver/pkg/server/filters/patch_optin_retry.go

@@ -0,0 +1,40 @@
+/*
+Copyright 2021 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package filters
+
+import (
+	"net/http"
+)
+
+func WithOptInRetryAfter(handler http.Handler, initializedFn func() bool) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		var retryAfter bool
+		if value := req.Header.Get("X-OpenShift-Internal-If-Not-Ready"); value == "reject" {
+			// the caller opted in for the request to be rejected if the server is not ready
+			retryAfter = !initializedFn()
+		}
+
+		if !retryAfter {
+			handler.ServeHTTP(w, req)
+			return
+		}
+
+		// Return a 429 status asking the client to try again after 5 seconds
+		w.Header().Set("Retry-After", "5")
+		http.Error(w, "The apiserver hasn't been fully initialized yet, please try again later.", http.StatusTooManyRequests)
+	})
+}

staging/src/k8s.io/apiserver/pkg/server/patch_config.go

@@ -37,3 +37,14 @@ func (c *Config) newIsTerminatingFunc() func() bool {
 		}
 	}
 }
+
+func (c *Config) newServerFullyInitializedFunc() func() bool {
+	return func() bool {
+		select {
+		case <-c.lifecycleSignals.HasBeenReady.Signaled():
+			return true
+		default:
+			return false
+		}
+	}
+}