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从互联网(或可信镜像仓库库以外的任何地方)拉取未知镜像会带来风险——例如恶意软件。但是还有其他很好的理由来维护单一的可信来源,例如在企业中实现可支持性。通过确保镜像仅来自受信任的镜像仓库,可以密切控制镜像库存,降低软件熵和蔓延的风险,并提高集群的整体安全性。除此以外,有时还会需要检查镜像的 tag,比如禁止使用 latest 镜像。
这今天我们尝试用“策略即代码”的实现 OPA 来实现功能。
还没开始之前可能有人会问:明明可以实现个 Admission Webhook 就行,为什么还要加上 OPA?
确实可以,但是这样策略和逻辑都会耦合在一起,当策略需要调整的时候需要修改代码重新发布。而 OPA 就是用来做解耦的,其更像是一个策略的执行引擎。
Open Policy Agent(以下简称 OPA,发音 “oh-pa”)一个开源的通用策略引擎,可以统一整个堆栈的策略执行。OPA 提供了一种高级声明性语言(Rego),可让你将策略指定为代码和简单的 API,以从你的软件中卸载策略决策。你可以使用 OPA 在微服务、Kubernetes、CI/CD 管道、API 网关等中实施策略。
Rego 是一种高级的声明性语言,是专门为 OPA 建立的。更多 OPA 的介绍可以看 Open Policy Agent 官网,不想看英文直接看这里。
现在进入正题。
启动 minikube
minikube start
创建并切换到命名空间 opa
(命名空间的切换使用 kubens,更多工具介绍见这里)
kubectl create namespace opa
kubens opa
Kubernetes 和 OPA 间的通信必须使用 TLS 进行保护。配置 TLS,使用 openssl
创建证书颁发机构(certificate authority CA)和 OPA 的证书/秘钥对。
openssl genrsa -out ca.key 2048
openssl req -x509 -new -nodes -key ca.key -days 100000 -out ca.crt -subj "/CN=admission_ca"
为 OPA 创建 TLS 秘钥和证书:
cat >server.conf <<EOF
[req]
req_extensions = v3_req
distinguished_name = req_distinguished_name
prompt = no
[req_distinguished_name]
CN = opa.opa.svc
[ v3_req ]
basicConstraints = CA:FALSE
keyUsage = nonRepudiation, digitalSignature, keyEncipherment
extendedKeyUsage = clientAuth, serverAuth
subjectAltName = @alt_names
[alt_names]
DNS.1 = opa.opa.svc
EOF
注意
CN
和alt_names
必须与后面创建 OPA service 的匹配。
openssl genrsa -out server.key 2048
openssl req -new -key server.key -out server.csr -config server.conf
openssl x509 -req -in server.csr -CA ca.crt -CAkey ca.key -CAcreateserial -out server.crt -days 100000 -extensions v3_req -extfile server.conf
为 OPA 创建保存 TLS 凭证的 Secret:
kubectl create secret tls opa-server --cert=server.crt --key=server.key
将 OPA 部署为准入控制器(admission controller)。
admission-controller.yaml
:
# 授权 OPA/kube-mgmt 对资源的只读权限 # kube-mgmt 会同步资源信息给 OPA,以便在策略中使用 kind: ClusterRoleBinding apiVersion: rbac.authorization.k8s.io/v1 metadata: name: opa-viewer roleRef: kind: ClusterRole name: view apiGroup: rbac.authorization.k8s.io subjects: - kind: Group name: system:serviceaccounts:opa apiGroup: rbac.authorization.k8s.io --- # 为 OPA/kube-mgmt 定义角色来在 configmaps 中更新策略状态 kind: Role apiVersion: rbac.authorization.k8s.io/v1 metadata: namespace: opa name: configmap-modifier rules: - apiGroups: [""] resources: ["configmaps"] verbs: ["update", "patch"] --- # 为 OPA/kube-mgmt 授予角色 kind: RoleBinding apiVersion: rbac.authorization.k8s.io/v1 metadata: namespace: opa name: opa-configmap-modifier roleRef: kind: Role name: configmap-modifier apiGroup: rbac.authorization.k8s.io subjects: - kind: Group name: system:serviceaccounts:opa apiGroup: rbac.authorization.k8s.io --- kind: Service apiVersion: v1 metadata: name: opa namespace: opa spec: selector: app: opa ports: - name: https protocol: TCP port: 443 targetPort: 8443 --- apiVersion: apps/v1 kind: Deployment metadata: labels: app: opa namespace: opa name: opa spec: replicas: 1 selector: matchLabels: app: opa template: metadata: labels: app: opa name: opa spec: containers: # WARNING: OPA is NOT running with an authorization policy configured. This # means that clients can read and write policies in OPA. If you are # deploying OPA in an insecure environment, be sure to configure # authentication and authorization on the daemon. See the Security page for # details: https://www.openpolicyagent.org/docs/security.html. - name: opa image: openpolicyagent/opa:0.30.1-rootless args: - "run" - "--server" - "--tls-cert-file=/certs/tls.crt" - "--tls-private-key-file=/certs/tls.key" - "--addr=0.0.0.0:8443" - "--addr=http://127.0.0.1:8181" - "--log-format=json-pretty" - "--set=decision_logs.console=true" volumeMounts: - readOnly: true mountPath: /certs name: opa-server readinessProbe: httpGet: path: /health?plugins&bundle scheme: HTTPS port: 8443 initialDelaySeconds: 3 periodSeconds: 5 livenessProbe: httpGet: path: /health scheme: HTTPS port: 8443 initialDelaySeconds: 3 periodSeconds: 5 - name: kube-mgmt image: openpolicyagent/kube-mgmt:0.11 args: - "--replicate=v1/pods" volumes: - name: opa-server secret: secretName: opa-server --- kind: ConfigMap apiVersion: v1 metadata: name: opa-default-system-main namespace: opa data: main: | package system import data.kubernetes.validating.images main = { "apiVersion": "admission.k8s.io/v1beta1", "kind": "AdmissionReview", "response": response, } default uid = "" uid = input.request.uid response = { "allowed": false, "uid": uid, "status": { "reason": reason, }, } { reason = concat(", ", images.deny) reason != "" } else = {"allowed": true, "uid": uid}
kubectl apply -f admission-controller.yaml
接下来,生成将用于将 OPA 注册为准入控制器的 manifest。
cat > webhook-configuration.yaml <<EOF kind: ValidatingWebhookConfiguration apiVersion: admissionregistration.k8s.io/v1beta1 metadata: name: opa-validating-webhook webhooks: - name: validating-webhook.openpolicyagent.org rules: - operations: ["CREATE", "UPDATE"] apiGroups: ["*"] apiVersions: ["*"] resources: ["pods"] clientConfig: caBundle: $(cat ca.crt | base64 | tr -d '\n') service: namespace: opa name: opa EOF
生成的配置文件包含 CA 证书的 base64 编码,以便可以在 Kubernetes API 服务器和 OPA 之间建立 TLS 连接。
kubectl apply -f webhook-configuration.yaml
查看 OPA 日志:
kubectl logs -l app=opa -c opa -f
这里我们定义了对容器镜像的检查:
image-policy.rego
package kubernetes.validating.images
deny[msg] {
some i
input.request.kind.kind == "Pod"
image := input.request.object.spec.containers[i].image
endswith(image, ":latest")
msg := sprintf("Image '%v' used latest image", [image])
} {
some i
input.request.kind.kind == "Pod"
image := input.request.object.spec.containers[i].image
not startswith(image, "192.168.64.1:5000")
msg := sprintf("Image '%v' comes from untrusted registry", [image])
}
kubectl create configmap image-policy --from-file=image-policy.rego
检查 configmap 的 annotation openpolicyagent.org/policy-status
值是否 为 '{"status":"ok"}'
。否则,就要根据报错信息处理问题。
注:192.168.64.1:5000
是笔者本地容器运行的一个私有仓库。
version: '3.6'
services:
registry:
image: registry:2.7.1
container_name: registry
restart: always
environment:
REGISTRY_HTTP_ADDR: 0.0.0.0:5000
REGISTRY_STORAGE: filesystem
REGISTRY_STORAGE_DELETE_ENABLED: 'true'
REGISTRY_STORAGE_FILESYSTEM_ROOTDIRECTORY: /var/lib/registry
ports:
- '5000:5000'
volumes:
- '/Users/addo/Downloads/tmp/registry:/var/lib/registry'
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: null
labels:
run: web-server
name: web-server
spec:
containers:
- image: nginx:1.21.1
name: web-server
resources: {}
dnsPolicy: ClusterFirst
restartPolicy: Always
status: {}
kubectl apply -f pod-bad-repo.yaml
Error from server (Image 'nginx:1.21.1' comes from untrusted registry): error when creating "pod-bad-repo.yaml": admission webhook "validating-webhook.openpolicyagent.org" denied the request: Image 'nginx:1.21.1' comes from untrusted registry
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: null
labels:
run: web-server
name: web-server
spec:
containers:
- image: 192.168.64.1:5000/nginx:latest
name: web-server
resources: {}
dnsPolicy: ClusterFirst
restartPolicy: Always
status: {}
kubectl apply -f pod-bad-tag.yaml
Error from server (Image '192.168.64.1:5000/nginx:latest' used latest image): error when creating "pod-bad-tag.yaml": admission webhook "validating-webhook.openpolicyagent.org" denied the request: Image '192.168.64.1:5000/nginx:latest' used latest image
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: null
labels:
run: web-server
name: web-server
spec:
containers:
- image: 192.168.64.1:5000/nginx:1.21.1
name: web-server
resources: {}
dnsPolicy: ClusterFirst
restartPolicy: Always
status: {}
kubectl apply -f pod-ok.yaml
pod/web-server created
策略即代码,以代码的实现表达策略;在通过策略与执行引擎的解耦分离,让策略更加的灵活。
后面我们再探索 OPA 的更多场景。
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