kubernetes Adminssion Webhook 准入控制器 (ImagePolicyWebhook)

开头语

写在前面：如有问题，以你为准，

目前24年应届生，各位大佬轻喷，部分资料与图片来自网络

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/

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'))