Kubernetes 在集群级别应用Pod安全标准

Note
本教程仅适用于新集群。

Pod 安全准入（PSA）在 v1.23 及更高版本默认启用， 因为它升级到测试版（beta）。 Pod 安全准入是在创建 Pod 时应用 Pod 安全标准的准入控制器。 本教程将向你展示如何在集群级别实施 ​baseline ​Pod 安全标准， 该标准将标准配置应用于集群中的所有名称空间。

在开始之前

在你的工作站中安装以下内容：

• ​KinD ​
• ​kubectl​

正确选择要应用的 Pod 安全标准

Pod 安全准入 允许你使用以下模式应用内置的 Pod 安全标准: ​enforce​、​audit ​和 ​warn​。

要收集信息以便选择最适合你的配置的 Pod 安全标准，请执行以下操作：

1. 创建一个没有应用 Pod 安全标准的集群：

kind create cluster --name psa-wo-cluster-pss --image kindest/node:v1.23.0

输出类似于：

Creating cluster "psa-wo-cluster-pss" ...
✓ Ensuring node image (kindest/node:v1.23.0) 
✓ Preparing nodes   
✓ Writing configuration 
✓ Starting control-plane ️
✓ Installing CNI 
✓ Installing StorageClass 
Set kubectl context to "kind-psa-wo-cluster-pss"
You can now use your cluster with:

kubectl cluster-info --context kind-psa-wo-cluster-pss

Thanks for using kind! 

2. 将 kubectl 上下文设置为新集群：

kubectl cluster-info --context kind-psa-wo-cluster-pss

输出类似于：

Kubernetes control plane is running at https://127.0.0.1:61350 
CoreDNS is running at https://127.0.0.1:61350/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy

To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.

3. 获取集群中的名字空间列表：

kubectl get ns

输出类似于：

NAME                 STATUS   AGE
default              Active   9m30s
kube-node-lease      Active   9m32s
kube-public          Active   9m32s
kube-system          Active   9m32s
local-path-storage   Active   9m26s

4. 使用 ​--dry-run=server​ 来了解应用不同的 Pod 安全标准时会发生什么：
• Privileged

kubectl label --dry-run=server --overwrite ns --all \                    
pod-security.kubernetes.io/enforce=privileged

输出类似于：

namespace/default labeled
namespace/kube-node-lease labeled
namespace/kube-public labeled
namespace/kube-system labeled
namespace/local-path-storage labeled

• Baseline

kubectl label --dry-run=server --overwrite ns --all \
pod-security.kubernetes.io/enforce=baseline

输出类似于：

namespace/default labeled
namespace/kube-node-lease labeled
namespace/kube-public labeled
Warning: existing pods in namespace "kube-system" violate the new PodSecurity enforce level "baseline:latest"
Warning: etcd-psa-wo-cluster-pss-control-plane (and 3 other pods): host namespaces, hostPath volumes
Warning: kindnet-vzj42: non-default capabilities, host namespaces, hostPath volumes
Warning: kube-proxy-m6hwf: host namespaces, hostPath volumes, privileged
namespace/kube-system labeled
namespace/local-path-storage labeled

• Restricted

kubectl label --dry-run=server --overwrite ns --all \
pod-security.kubernetes.io/enforce=restricted

输出类似于：

namespace/default labeled
namespace/kube-node-lease labeled
namespace/kube-public labeled
Warning: existing pods in namespace "kube-system" violate the new PodSecurity enforce level "restricted:latest"
Warning: coredns-7bb9c7b568-hsptc (and 1 other pod): unrestricted capabilities, runAsNonRoot != true, seccompProfile
Warning: etcd-psa-wo-cluster-pss-control-plane (and 3 other pods): host namespaces, hostPath volumes, allowPrivilegeEscalation != false, unrestricted capabilities, restricted volume types, runAsNonRoot != true
Warning: kindnet-vzj42: non-default capabilities, host namespaces, hostPath volumes, allowPrivilegeEscalation != false, unrestricted capabilities, restricted volume types, runAsNonRoot != true, seccompProfile
Warning: kube-proxy-m6hwf: host namespaces, hostPath volumes, privileged, allowPrivilegeEscalation != false, unrestricted capabilities, restricted volume types, runAsNonRoot != true, seccompProfile
namespace/kube-system labeled
Warning: existing pods in namespace "local-path-storage" violate the new PodSecurity enforce level "restricted:latest"
Warning: local-path-provisioner-d6d9f7ffc-lw9lh: allowPrivilegeEscalation != false, unrestricted capabilities, runAsNonRoot != true, seccompProfile
namespace/local-path-storage labeled

从前面的输出中，你会注意到应用 ​privileged ​Pod 安全标准不会显示任何名字空间的警告。 然而，​baseline ​和 ​restricted ​标准都有警告，特别是在 ​kube-system​ 名字空间中。

设置模式、版本和标准

在本节中，你将以下 Pod 安全标准应用于最新（​latest​）版本：

• 在 ​enforce ​模式下的 ​baseline ​标准。
• ​warn ​和 ​audit ​模式下的 ​restricted ​标准。

​baseline ​Pod 安全标准提供了一个方便的中间立场，能够保持豁免列表简短并防止已知的特权升级。

此外，为了防止 ​kube-system​ 中的 Pod 失败，你将免除该名字空间应用 Pod 安全标准。

在你自己的环境中实施 Pod 安全准入时，请考虑以下事项：

1. 根据应用于集群的风险状况，更严格的 Pod 安全标准（如 ​restricted​）可能是更好的选择。
2. 对 ​kube-system​ 名字空间进行赦免会允许 Pod 在其中以 ​privileged ​模式运行。 对于实际使用，Kubernetes 项目强烈建议你应用严格的 RBAC 策略来限制对 ​kube-system​ 的访问， 遵循最小特权原则。
3. 创建一个配置文件，Pod 安全准入控制器可以使用该文件来实现这些 Pod 安全标准：

mkdir -p /tmp/pss
cat <<EOF > /tmp/pss/cluster-level-pss.yaml 
apiVersion: apiserver.config.k8s.io/v1
kind: AdmissionConfiguration
plugins:
- name: PodSecurity
  configuration:
    apiVersion: pod-security.admission.config.k8s.io/v1beta1
    kind: PodSecurityConfiguration
    defaults:
      enforce: "baseline"
      enforce-version: "latest"
      audit: "restricted"
      audit-version: "latest"
      warn: "restricted"
      warn-version: "latest"
    exemptions:
      usernames: []
      runtimeClasses: []
      namespaces: [kube-system]
EOF

4. 在创建集群时配置 API 服务器使用此文件：

cat <<EOF > /tmp/pss/cluster-config.yaml 
kind: Cluster
apiVersion: kind.x-k8s.io/v1alpha4
nodes:
- role: control-plane
  kubeadmConfigPatches:
  - |
    kind: ClusterConfiguration
    apiServer:
        extraArgs:
          admission-control-config-file: /etc/config/cluster-level-pss.yaml
        extraVolumes:
          - name: accf
            hostPath: /etc/config
            mountPath: /etc/config
            readOnly: false
            pathType: "DirectoryOrCreate"
  extraMounts:
  - hostPath: /tmp/pss
    containerPath: /etc/config
    # optional: if set, the mount is read-only.
    # default false
    readOnly: false
    # optional: if set, the mount needs SELinux relabeling.
    # default false
    selinuxRelabel: false
    # optional: set propagation mode (None, HostToContainer or Bidirectional)
    # see https://kubernetes.io/docs/concepts/storage/volumes/#mount-propagation
    # default None
    propagation: None
EOF

说明：
如果你在 macOS 上使用 Docker Desktop 和 KinD， 你可以在菜单项 Preferences > Resources > File Sharing 下添加 ​/tmp​ 作为共享目录。

5. 创建一个使用 Pod 安全准入的集群来应用这些 Pod 安全标准：

kind create cluster --name psa-with-cluster-pss --image kindest/node:v1.23.0 --config /tmp/pss/cluster-config.yaml

输出类似于：

Creating cluster "psa-with-cluster-pss" ...
 ✓ Ensuring node image (kindest/node:v1.23.0)  
 ✓ Preparing nodes   
 ✓ Writing configuration  
 ✓ Starting control-plane ️ 
 ✓ Installing CNI  
 ✓ Installing StorageClass  
Set kubectl context to "kind-psa-with-cluster-pss"
You can now use your cluster with:

kubectl cluster-info --context kind-psa-with-cluster-pss

Have a question, bug, or feature request? Let us know! https://kind.sigs.k8s.io/#community 

6. 将 kubectl 指向集群

kubectl cluster-info --context kind-psa-with-cluster-pss

输出类似于：

Kubernetes control plane is running at https://127.0.0.1:63855
CoreDNS is running at https://127.0.0.1:63855/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy

To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.

7. 创建以下 Pod 规约作为在 default 名字空间中的一个最小配置：

cat <<EOF > /tmp/pss/nginx-pod.yaml
apiVersion: v1
kind: Pod
metadata:
  name: nginx
spec:
  containers:
    - image: nginx
      name: nginx
      ports:
        - containerPort: 80
EOF

8. 在集群中创建 Pod：

kubectl apply -f /tmp/pss/nginx-pod.yaml

输出类似于：

Warning: would violate PodSecurity "restricted:latest": allowPrivilegeEscalation != false (container "nginx" must set securityContext allowPrivilegeEscalation=false), unrestricted capabilities (container "nginx" must set securityContext.capabilities.drop=["ALL"]), runAsNonRoot != true (pod or container "nginx" must set securityContext.runAsNonRoot=true), seccompProfile (pod or container "nginx" must set securityContext seccompProfile.type to "RuntimeDefault" or "Localhost")
pod/nginx created

清理

运行 ​kind delete cluster --name psa-with-cluster-pss​ 和 ​kind delete cluster --name psa-wo-cluster-pss​ 来删除你创建的集群。