kubernetes Adminssion Webhook 准入控制器 (ImagePolicyWebhook)

开头语

写在前面：如有问题，以你为准，

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介绍 原理 流程

Admission Webhook 准入控制器Vebhook是准入控制插件的一种，用于拦截所有向APISERVER发送的 请求，并且可以修改请求或拒绝请求。

即拦截进出的流量，对k8s来说即为apiserver的请求

Admission webhook 为开发者提供了非常灵活的插件模式，在kubernetes资源持久化，之前，管理员通过程序 可以对指定资源做校验、修改等操作。例如为资源自动打标签、pod设置默认SA,自动注入sidecar容器等。

https://kubernetes.io/zh-cn/docs/reference/access-authn-authz/admission-controllers/

相关Vebhook.准入控制器：

webhook 是一个api，用于处理一个轻量级的事件

1. MutatingAdmissionWebhook? 修改资源，理论上可以监听并修改任何经过ApiServer处理的请求
2. ValidatingAdmissionWebhook 验证资源
3. ImagePolicyWebhook????????????? 镜像策略，主要验证镜像字段是否满足条件 (仓库，tag)

流程：当 api 接收到这个请求后，并进行身份验证授权（Authentication），通过调用准入控制的接口来处理传入过来的资源，资源会传入到Webhook（Mutating），进行对象架构验证（object），再进行资源验证，查看字段是否符合要求（Validating），最后传入etcd中（Persisted to etcd）

ImagePolicyWebhook

架构

本次示例使用的方法是

通过docker 跑一个能进行api检测的python程序

通过将传给apiserver创建pod api 传到python docker 上进行检测镜像版本标签

如果不带标签则返回给apiserver拒绝语句，如果带标签则返回接收语句

启用

mkdir /etc/kubernetes/image-policy/

vim admission_configuration.yaml

apiVersion: apiserver.config.k8s.io/v1

kind: AdmissionConfiguration

plugins:

- name: ImagePolicyWebhook

? configuration:???

??? imagePolicy:

????? kubeConfigFile: /etc/kubernetes/image-policy/connect_webhook.yaml

????? # 链接镜像策略服务器配置文件

????? # 以秒计的时长，控制批准请求的缓存时间

????? allowTTL: 50

????? # 以秒计的时长，控制拒绝请求的缓存时间

????? denyTTL: 50

????? # 以毫秒计的时长，控制重试间隔

????? retryBackoff: 500

????? # 确定 Webhook 后端失效时的行为

????? defaultAllow: true

[root@master opa]# cp /root/.kube/config /etc/kubernetes/image-policy/connect_webhook.yaml

[root@master opa]# vim /etc/kubernetes/image-policy/connect_webhook.yaml

zip文件在最顶部

[root@master webhook]# unzip image-policy-webhook.zip

Archive:? image-policy-webhook.zip

?? creating: image-policy-webhook/

? inflating: image-policy-webhook/Dockerfile

? inflating: image-policy-webhook/main.py

? inflating: admission_configuration.yaml

? inflating: connect_webhook.yaml

? inflating: image-policy-certs.sh

[root@master image-policy-webhook]# docker pull library/python

Using default tag: latest

latest: Pulling from library/python

8457fd5474e7: Pull complete

13baa2029dde: Pull complete

[root@master image-policy-webhook]# docker build -t webhook-python .

Sending build context to Docker daemon? 3.584kB

Step 1/9 : FROM python

?---> a5d7930b60cc

Step 2/9 : RUN useradd python

?---> Running in 6a893ebbc97e

[root@master webhook]# chmod +x image-policy-certs.sh

[root@master webhook]# ./image-policy-certs.sh

2023/11/15 22:18:52 [INFO] generating a new CA key and certificate from CSR

2023/11/15 22:18:52 [INFO] generate received request

2023/11/15 22:18:52 [INFO] received CSR

2023/11/15 22:18:52 [INFO] generating key: rsa-2048

2023/11/15 22:18:52 [INFO] encoded CSR

2023/11/15 22:18:52 [INFO] signed certificate with serial number 39827921930120332354958212009020451382931127285

2023/11/15 22:18:52 [INFO] generate received request

2023/11/15 22:18:52 [INFO] received CSR

2023/11/15 22:18:52 [INFO] generating key: rsa-2048

2023/11/15 22:18:52 [INFO] encoded CSR

2023/11/15 22:18:52 [INFO] signed certificate with serial number 157085660290104533426640490732748948028109129205

2023/11/15 22:18:52 [INFO] generate received request

2023/11/15 22:18:52 [INFO] received CSR

2023/11/15 22:18:52 [INFO] generating key: rsa-2048

2023/11/15 22:18:53 [INFO] encoded CSR

2023/11/15 22:18:53 [INFO] signed certificate with serial number 20452152514611241358495370727393457709691078555

2023/11/15 22:18:53 [WARNING] This certificate lacks a "hosts" field. This makes it unsuitable for

websites. For more information see the Baseline Requirements for the Issuance and Management

of Publicly-Trusted Certificates, v.1.1.6, from the CA/Browser Forum (https://cabforum.org);

specifically, section 10.2.3 ("Information Requirements").

[root@master webhook]# ls

admission_configuration.yaml? apiserver-client.pem? ca-key.pem???????????? image-policy-webhook????? webhook-key.pem

apiserver-client.csr????????? ca-config.json??????? ca.pem???????????????? image-policy-webhook.zip? webhook.pem

apiserver-client-csr.json???? ca.csr??????????????? connect_webhook.yaml?? webhook.csr

apiserver-client-key.pem????? ca-csr.json?????????? image-policy-certs.sh? webhook-csr.json

[root@master webhook]# cp webhook* image-policy-webhook

[root@master webhook]# cd image-policy-webhook/


docker run -d -u root --name=webhook-python \

-v $PWD/webhook.pem:/data/www/webhook.pem \

-v $PWD/webhook-key.pem:/data/www/webhook-key.pem \

-e PYTHONUNBUFFERED=1 -p 8080:8080 \

webhook-python

[root@master image-policy-webhook]# docker ps -a | grep python

fe9713e647e8?? webhook-python????????????????????????????????????? "/bin/sh -c 'python …"?? 11 seconds ago?? Exited (1) 9 seconds ago???????????? webhook-python

[root@master webhook]# cp /root/k8s/cks/webhook/webhook.pem /etc/kubernetes/image-policy/

[root@master webhook]# cp /root/k8s/cks/webhook/apiserver-client-key.pem /etc/kubernetes/image-policy/

[root@master webhook]# cp /root/k8s/cks/webhook/apiserver-client.pem /etc/kubernetes/image-policy/

[root@master webhook]# ls /etc/kubernetes/image-policy/

admission_configuration.yaml? apiserver-client-key.pem? apiserver-client.pem? connect_webhook.yaml? webhook.pem

下面文件的 /etc/kubernetes/image-policy 是容器内的路径

apiVersion: v1

kind: Config

clusters:

- cluster:

??? certificate-authority: /etc/kubernetes/image-policy/webhook.pem # 数字证书，用于验证远程服务

??? server: https://192.168.100.53:8080/image_policy # 镜像策略服务器地址，必须是https

? name: webhook

contexts:

- context:

??? cluster: webhook

??? user: apiserver

? name: webhook

current-context: webhook

preferences: {}

users:

- name: apiserver

? user:

??? client-certificate: /etc/kubernetes/image-policy/apiserver-client.pem # webhook准入控制器使用的证书

??? client-key: /etc/kubernetes/image-policy/apiserver-client-key.pem # 对应私钥证书

开启插件并使用hostpath 数据卷将宿主机/etc/kubernetes/image-policy目录挂载到容器中

??? - --enable-admission-plugins=NodeRestriction,ImagePolicyWebhook?

??? - --admission-control-config-file=/etc/kubernetes/image-policy/admission_configuration.yaml

# 挂载卷添加



??? - mountPath: /etc/kubernetes/image-policy

????? name: image-policy

?????



? - hostPath:

????? path: /etc/kubernetes/image-policy

????? type: DirectoryOrCreate

??? name: image-policy

systemctl restart kubelet

测试

是通过python docker 中的python函数进行判断的是否执行创建操作

[root@master image-policy-webhook]# kubectl run web --image=nginx

Error from server (Forbidden): pods "web" is forbidden: image policy webhook backend denied one or more images: 检查镜像失败！镜像标签不允许使用latest!

[root@master image-policy-webhook]# kubectl run web --image=nginx:1.17.1

pod/web created

[root@master image-policy-webhook]# kubectl get pod

NAME?? READY?? STATUS??? RESTARTS?? AGE

web??? 1/1???? Running?? 0????????? 5s

策略解析（python）

镜像中的python程序

from flask import Flask,request
import json

app = Flask(__name__)

@app.route('/image_policy',methods=["POST"])
def image_policy():
    post_data = request.get_data().decode()
    #print("POST数据: %s" %post_data)
    data = json.loads(post_data)
    for c in data['spec']['containers']:
        if ":" not in c['image'] or ":latest" in c['image']:  # 如果镜像里不带冒号或者带:latest说明是镜像使用latest标签
            allowed, reason = False, "检查镜像失败！镜像标签不允许使用latest!"
            break
        else:
            allowed, reason = True, "检查镜像通过."
    print("检查结果: %s" %reason)
    result = {"apiVersion": "imagepolicy.k8s.io/v1alpha1","kind": "ImageReview",
              "status": {"allowed": allowed,"reason": reason}}

    return json.dumps(result,ensure_ascii=False)

if __name__ == "__main__":
    app.run(host="0.0.0.0",port=8080,ssl_context=('/data/www/webhook.pem','/data/www/webhook-key.pem'))