webhook source code

test/images/webhook/Dockerfile

+# Copyright 2017 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.
+
+FROM alpine:latest
+
+ADD webhook /webhook
+ENTRYPOINT ["/webhook"]

test/images/webhook/Makefile

+# Copyright 2017 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.
+
+build:
+	CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o webhook .
+	docker build --no-cache -t gcr.io/kubernetes-e2e-test-images/k8s-sample-admission-webhook-amd64:1.8v1 .
+push:
+	gcloud docker --push gcr.io/kubernetes-e2e-test-images/k8s-sample-admission-webhook-amd64:1.8v1 .

test/images/webhook/README.md

+# Kubernetes External Admission Webhook Example
+
+The example shows how to build and deploy an external webhook that only admits
+pods creation and update if the container images have the "grc.io" prefix.
+
+## Prerequisites
+
+Please use a Kubernetes release at least as new as v1.8.0 or v1.9.0-alpha.1,
+because the generated server cert/key only works with Kubernetes release that
+contains this [change](https://github.com/kubernetes/kubernetes/pull/50476).
+Please checkout the `pre-v1.8` tag for an example that works with older
+clusters.
+
+Please enable the admission webhook feature
+([doc](https://kubernetes.io/docs/admin/extensible-admission-controllers/#enable-external-admission-webhooks)).
+
+## Build the code
+
+```bash
+make build
+```
+
+## Deploy the code
+
+```bash
+make deploy-only 
+```
+
+The Makefile assumes your cluster is created by the
+[hack/local-up-cluster.sh](https://github.com/kubernetes/kubernetes/blob/master/hack/local-up-cluster.sh).
+Please modify the Makefile accordingly if your cluster is created differently.
+
+## Explanation on the CAs/Certs/Keys
+
+The apiserver initiates a tls connection with the webhook, so the apiserver is
+the tls client, and the webhook is the tls server.
+
+The webhook proves its identity by the `serverCert` in the certs.go. The server
+cert is signed by the CA in certs.go. To let the apiserver trust the `caCert`,
+the webhook registers itself with the apiserver via the
+`admissionregistration/v1alpha1/externalAdmissionHook` API, with
+`clientConfig.caBundle=caCert`.
+
+For maximum protection, this example webhook requires and verifies the client
+(i.e., the apiserver in this case) cert. The cert presented by the apiserver is
+signed by a client CA, whose cert is stored in the configmap
+`extension-apiserver-authentication` in the `kube-system` namespace. See the
+`getAPIServerCert` function for more information. Usually you don't need to
+worry about setting up this CA cert. It's taken care of when the cluster is
+created. You can disable the client cert verification by setting the
+`tls.Config.ClientAuth` to `tls.NoClientCert` in `config.go`.

test/images/webhook/config.go

+/*
+Copyright 2017 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 main
+
+import (
+	"crypto/tls"
+
+	"k8s.io/client-go/kubernetes"
+	"k8s.io/client-go/rest"
+
+	"github.com/golang/glog"
+)
+
+// Get a clientset with in-cluster config.
+func getClient() *kubernetes.Clientset {
+	config, err := rest.InClusterConfig()
+	if err != nil {
+		glog.Fatal(err)
+	}
+	clientset, err := kubernetes.NewForConfig(config)
+	if err != nil {
+		glog.Fatal(err)
+	}
+	return clientset
+}
+
+func configTLS(config Config, clientset *kubernetes.Clientset) *tls.Config {
+	sCert, err := tls.LoadX509KeyPair(config.CertFile, config.KeyFile)
+	if err != nil {
+		glog.Fatal(err)
+	}
+	return &tls.Config{
+		Certificates: []tls.Certificate{sCert},
+		// TODO: uses mutual tls after we agree on what cert the apiserver should use.
+		// ClientAuth:   tls.RequireAndVerifyClientCert,
+	}
+}

test/images/webhook/main.go

+/*
+Copyright 2017 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 main
+
+import (
+	"encoding/json"
+	"flag"
+	"io/ioutil"
+	"net/http"
+	"strings"
+
+	"github.com/golang/glog"
+	"k8s.io/api/admission/v1alpha1"
+	"k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+)
+
+// Config contains the server (the webhook) cert and key.
+type Config struct {
+	CertFile string
+	KeyFile  string
+}
+
+func (c *Config) addFlags() {
+	flag.StringVar(&c.CertFile, "tls-cert-file", c.CertFile, ""+
+		"File containing the default x509 Certificate for HTTPS. (CA cert, if any, concatenated "+
+		"after server cert).")
+	flag.StringVar(&c.KeyFile, "tls-private-key-file", c.KeyFile, ""+
+		"File containing the default x509 private key matching --tls-cert-file.")
+}
+
+// only allow pods to pull images from specific registry.
+func admit(data []byte) *v1alpha1.AdmissionReviewStatus {
+	ar := v1alpha1.AdmissionReview{}
+	if err := json.Unmarshal(data, &ar); err != nil {
+		glog.Error(err)
+		return nil
+	}
+	podResource := metav1.GroupVersionResource{Group: "", Version: "v1", Resource: "pods"}
+	if ar.Spec.Resource != podResource {
+		glog.Errorf("expect resource to be %s", podResource)
+		return nil
+	}
+
+	raw := ar.Spec.Object.Raw
+	pod := v1.Pod{}
+	if err := json.Unmarshal(raw, &pod); err != nil {
+		glog.Error(err)
+		return nil
+	}
+	reviewStatus := v1alpha1.AdmissionReviewStatus{}
+	reviewStatus.Allowed = true
+	// Note: the apiserver encodes the api.Pod. Decoding it as a v1.Pod will
+	// lose the metadata. So the following check on labels will not work
+	// until we let the apiserver encodes the versioned object.
+	for k, v := range pod.Labels {
+		if k == "webhook-e2e-test" && v == "webhook-disallow" {
+			reviewStatus.Allowed = false
+			reviewStatus.Result = &metav1.Status{
+				Reason: "the pod contains unwanted label",
+			}
+		}
+	}
+	for _, container := range pod.Spec.Containers {
+		if strings.Contains(container.Name, "webhook-disallow") {
+			reviewStatus.Allowed = false
+			reviewStatus.Result = &metav1.Status{
+				Message: "the pod contains unwanted container name",
+			}
+		}
+	}
+	return &reviewStatus
+}
+
+func serve(w http.ResponseWriter, r *http.Request) {
+	var body []byte
+	if r.Body != nil {
+		if data, err := ioutil.ReadAll(r.Body); err == nil {
+			body = data
+		}
+	}
+
+	// verify the content type is accurate
+	contentType := r.Header.Get("Content-Type")
+	if contentType != "application/json" {
+		glog.Errorf("contentType=%s, expect application/json", contentType)
+		return
+	}
+
+	reviewStatus := admit(body)
+	ar := v1alpha1.AdmissionReview{
+		Status: *reviewStatus,
+	}
+
+	resp, err := json.Marshal(ar)
+	if err != nil {
+		glog.Error(err)
+	}
+	if _, err := w.Write(resp); err != nil {
+		glog.Error(err)
+	}
+}
+
+func main() {
+	var config Config
+	config.addFlags()
+	flag.Parse()
+
+	http.HandleFunc("/", serve)
+	clientset := getClient()
+	server := &http.Server{
+		Addr:      ":443",
+		TLSConfig: configTLS(config, clientset),
+	}
+	server.ListenAndServeTLS("", "")
+}