k8s实践：快速开发自己的 K8S Adminssion Webhook

准入控制器介绍

准入 Webhook 是一种用于接收准入请求并对其进行处理的 HTTP 回调机制。可以定义两种类型的准入 Webhook，即验证性质的准入 Webhook和变更性质的准入 Webhook。变更性质的准入 Webhook 会先被调用。它们可以修改发送到 API 服务器的对象以执行自定义的设置默认值操作。

在完成了所有对象修改并且 API 服务器也验证了所传入的对象之后，验证性质的 Webhook 会被调用，并通过拒绝请求的方式来强制实施自定义的策略。

kubewebhook example 准入控制器部署

我们使用 kubewebhook 库来开发自己的准入控制器，kubewebhook 库支持以下特性：

简单上手、可扩展以及使用灵活
支持验证类型和变更类型的 Webhook
支持 K8S 原生资源和用户 CRD 资源
灵活组装多个 Webhook 在同一个服务
提供 Webhook metrics 指标和 Tracing 指标

部署

官方部署步骤

首先在集群中部署 kubewebhook 库的 pod-annotate 例子来验证一下功能，K8S集群版本是 v1.22，部署步骤如下所示：

更新 SSL 证书：cd examples && bash create-certs.sh
部署 Webhook 证书资源：kubectl apply -f ./pod-annotate/deploy/webhook-certs.yaml
部署 Webhook 服务：kubectl apply -f ./pod-annotate/deploy/webhook.yaml
注册 mutating webhook 配置到 apiserver：kubectl apply -f ./pod-annotate/deploy/webhook-registration.yaml

使用验证的 deployment 验证 Webhook 功能：kubectl apply -f ./pod-annotate/deploy/test-deployment.yaml，发现 pod 无法成功创建。

nginx-test replicas 事件如下：

✗ k describe rs nginx-test-6799fc88d8
...
Conditions:
  Type             Status  Reason
  ----             ------  ------
  ReplicaFailure   True    FailedCreate
Events:
  Type     Reason        Age                From                   Message
  ----     ------        ----               ----                   -------
  Warning  FailedCreate  3s (x13 over 23s)  replicaset-controller  Error creating: Internal error occurred: failed calling webhook "pod-annotate-webhook.slok.dev": failed to call webhook: Post "https://pod-annotate-webhook.default.svc:443/mutate?timeout=10s": x509: certificate relies on legacy Common Name field, use SANs or temporarily enable Common Name matching with GODEBUG=x509ignoreCN=0

webhook 服务日志：

✗ k logs -f pod-annotate-webhook-6b69f49879-7thgt
2024/08/20 05:24:07 [INFO] Listening on :8080
2024/08/20 05:24:47 http: TLS handshake error from 10.165.112.169:25265: remote error: tls: bad certificate
2024/08/20 05:24:47 http: TLS handshake error from 10.165.112.169:25267: remote error: tls: bad certificate
2024/08/20 05:24:47 http: TLS handshake error from 10.165.112.169:25271: remote error: tls: bad certificate
2024/08/20 05:24:47 http: TLS handshake error from 10.165.112.169:25273: remote error: tls: bad certificate

问题排查

结合 Kubernetes Admission Webhook 部署和调试和阳明大佬的 admission-webhook-example 项目等资料，找到了解决方法。

创建证书的脚本 create-certs.sh 文件需要做如下调整：

1、生成 webhookCA.csr 证书文件需要引入 csr.conf 配置文件

cat <<EOF >> ./csr.conf
[req]
req_extensions = v3_req
distinguished_name = req_distinguished_name
[req_distinguished_name]
[ v3_req ]
basicConstraints = CA:FALSE
keyUsage = nonRepudiation, digitalSignature, keyEncipherment
extendedKeyUsage = serverAuth
subjectAltName = @alt_names
[alt_names]
DNS.1 = ${WEBHOOK_SVC}
DNS.2 = ${WEBHOOK_SVC}.${WEBHOOK_NS}
DNS.3 = ${WEBHOOK_SVC}.${WEBHOOK_NS}.svc
EOF

openssl req -new -key ./webhookCA.key -days 36500 -subj "/CN=system:node:${WEBHOOK_SVC}.${WEBHOOK_NS}.svc/O=system:nodes" -out ./webhookCA.csr -config csr.conf

2、使用 k8s 默认的证书管理机制颁发 webhook.crt 证书

CSR_NAME="${WEBHOOK_SVC}-${WEBHOOK_NS}"
kubectl delete csr ${CSR_NAME} 2>/dev/null || true

cat <<EOF | kubectl create -f -
apiVersion: certificates.k8s.io/v1
kind: CertificateSigningRequest
metadata:
  name: ${CSR_NAME}
spec:
  signerName: kubernetes.io/kubelet-serving
  groups:
  - system:authenticated
  request: $(cat ./webhookCA.csr | base64 | tr -d '\n')
  usages:
  - digital signature
  - key encipherment
  - server auth
EOF

kubectl certificate approve ${CSR_NAME}

kubectl get csr ${CSR_NAME} -o jsonpath='{.status.certificate}' | openssl base64 -d -A -out ./webhook.crt

3、获取 ca 证书方式更新

CA_BUNDLE=$(kubectl get configmap -n kube-system extension-apiserver-authentication  -o=jsonpath='{.data.client-ca-file}' | base64 -w0)

更新完 create-certs.sh 脚本文件后最终部署成功，nginx-test 应用 pod 注解也自动注入成功。

开发自己的准入控制器

以我们自己的一个需求为例：给 deployment 资源中 logkit 容器环境变量中注入一些环境信息。

更新 webhook 代码

直接照着 pod-annotate 示例代码改：

diff --git a/examples/pod-annotate/main.go b/examples/pod-annotate/main.go
index 135490e..0138444 100644
--- a/examples/pod-annotate/main.go
+++ b/examples/pod-annotate/main.go
@@ -7,6 +7,7 @@ import (
 	"net/http"
 	"os"

+	appsv1 "k8s.io/api/apps/v1"
 	corev1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"

@@ -17,22 +18,26 @@ import (
 	kwhmutating "github.com/slok/kubewebhook/v2/pkg/webhook/mutating"
 )

-func annotatePodMutator(_ context.Context, _ *kwhmodel.AdmissionReview, obj metav1.Object) (*kwhmutating.MutatorResult, error) {
-	pod, ok := obj.(*corev1.Pod)
+func injectLogkitEnvMutator(_ context.Context, _ *kwhmodel.AdmissionReview, obj metav1.Object) (*kwhmutating.MutatorResult, error) {
+	deploy, ok := obj.(*appsv1.Deployment)
 	if !ok {
 		// If not a pod just continue the mutation chain(if there is one) and don't do nothing.
 		return &kwhmutating.MutatorResult{}, nil
 	}

-	// Mutate our object with the required annotations.
-	if pod.Annotations == nil {
-		pod.Annotations = make(map[string]string)
+	containers := deploy.Spec.Template.Spec.Containers
+	for i, c := range containers {
+		if c.Name == "logkit" {
+			c.Env = append(c.Env, corev1.EnvVar{
+				Name:  "FOO",
+				Value: "BAR",
+			})
+			containers[i].Env = c.Env
+		}
 	}
-	pod.Annotations["mutated"] = "true"
-	pod.Annotations["mutator"] = "pod-annotate"

 	return &kwhmutating.MutatorResult{
-		MutatedObject: pod,
+		MutatedObject: deploy,
 	}, nil
 }

@@ -60,11 +65,11 @@ func main() {
 	cfg := initFlags()

 	// Create our mutator
-	mt := kwhmutating.MutatorFunc(annotatePodMutator)
+	mt := kwhmutating.MutatorFunc(injectLogkitEnvMutator)

 	mcfg := kwhmutating.WebhookConfig{
-		ID:      "podAnnotate",
-		Obj:     &corev1.Pod{},
+		ID:      "injectLogkitEnv",
+		Obj:     &appsv1.Deployment{},
 		Mutator: mt,
 		Logger:  logger,
 	}

更新 webhook 配置

diff --git a/examples/pod-annotate/deploy/webhook-registration.yaml.tpl b/examples/pod-annotate/deploy/webhook-registration.yaml.tpl
index ff11b68..09a21f8 100644
--- a/examples/pod-annotate/deploy/webhook-registration.yaml.tpl
+++ b/examples/pod-annotate/deploy/webhook-registration.yaml.tpl
@@ -1,4 +1,4 @@
-apiVersion: admissionregistration.k8s.io/v1beta1
+apiVersion: admissionregistration.k8s.io/v1
 kind: MutatingWebhookConfiguration
 metadata:
   name: pod-annotate-webhook
@@ -7,6 +7,9 @@ metadata:
     kind: mutator
 webhooks:
   - name: pod-annotate-webhook.slok.dev
+    admissionReviewVersions:
+    - v1
+    - v1beta1
     clientConfig:
       service:
         name: pod-annotate-webhook
@@ -15,7 +18,11 @@ webhooks:
       caBundle: CA_BUNDLE
     rules:
       - operations: [ "CREATE" ]
-        apiGroups: [""]
+        apiGroups: ["apps"]
         apiVersions: ["v1"]
-        resources: ["pods"]
+        resources: ["deployments"]
+    namespaceSelector:
+      matchLabels:
+        kubernetes.io/metadata.name: demo
+    sideEffects: None

完整项目链接：https://github.com/wenhuwang/K8S-Learning-And-Pratice/tree/main/webhook/mutating/deployment-inject-env

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Last updated 25 days ago