Apply Pod Security Standards at the Cluster Level

Pod Security is an admission controller that carries out checks against the Kubernetes Pod Security Standards when new pods are created. It is a feature GA'ed in v1.25. This tutorial shows you how to enforce the baseline Pod Security Standard at the cluster level which applies a standard configuration to all namespaces in a cluster.

To apply Pod Security Standards to specific namespaces, refer to Apply Pod Security Standards at the namespace level.

If you are running a version of Kubernetes other than v1.32, check the documentation for that version.

Before you begin

Install the following on your workstation:

• kind
• kubectl

This tutorial demonstrates what you can configure for a Kubernetes cluster that you fully control. If you are learning how to configure Pod Security Admission for a managed cluster where you are not able to configure the control plane, read Apply Pod Security Standards at the namespace level.

Choose the right Pod Security Standard to apply

Pod Security Admission lets you apply built-in Pod Security Standards with the following modes: enforce, audit, and warn.

To gather information that helps you to choose the Pod Security Standards that are most appropriate for your configuration, do the following:

1. Create a cluster with no Pod Security Standards applied:

   kind create cluster --name psa-wo-cluster-pss 

   The output is similar to:

   Creating cluster "psa-wo-cluster-pss" ... ✓ Ensuring node image (kindest/node:v1.32.0) 🖼 ✓ 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. Set the kubectl context to the new cluster:

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

   The output is similar to this:

   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. Get a list of namespaces in the cluster:

   kubectl get ns 

   The output is similar to this:

   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. Use --dry-run=server to understand what happens when different Pod Security Standards are applied:

   1. Privileged

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

      The output is similar to:

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

   2. Baseline

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

      The output is similar to:

      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 

   3. Restricted

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

      The output is similar to:

      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 

From the previous output, you'll notice that applying the privileged Pod Security Standard shows no warnings for any namespaces. However, baseline and restricted standards both have warnings, specifically in the kube-system namespace.

Set modes, versions and standards

In this section, you apply the following Pod Security Standards to the latest version:

• baseline standard in enforce mode.
• restricted standard in warn and audit mode.

The baseline Pod Security Standard provides a convenient middle ground that allows keeping the exemption list short and prevents known privilege escalations.

Additionally, to prevent pods from failing in kube-system, you'll exempt the namespace from having Pod Security Standards applied.

When you implement Pod Security Admission in your own environment, consider the following:

1. Based on the risk posture applied to a cluster, a stricter Pod Security Standard like restricted might be a better choice.

2. Exempting the kube-system namespace allows pods to run as privileged in this namespace. For real world use, the Kubernetes project strongly recommends that you apply strict RBAC policies that limit access to kube-system, following the principle of least privilege. To implement the preceding standards, do the following:

3. Create a configuration file that can be consumed by the Pod Security Admission Controller to implement these Pod Security Standards:

   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/v1 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 

   Note:

   pod-security.admission.config.k8s.io/v1 configuration requires v1.25+. For v1.23 and v1.24, use v1beta1. For v1.22, use v1alpha1.

4. Configure the API server to consume this file during cluster creation:

   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 

   Note:

   If you use Docker Desktop with kind on macOS, you can add /tmp as a Shared Directory under the menu item Preferences > Resources > File Sharing.

5. Create a cluster that uses Pod Security Admission to apply these Pod Security Standards:

   kind create cluster --name psa-with-cluster-pss --config /tmp/pss/cluster-config.yaml 

   The output is similar to this:

   Creating cluster "psa-with-cluster-pss" ... ✓ Ensuring node image (kindest/node:v1.32.0) 🖼 ✓ 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. Point kubectl to the cluster:

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

   The output is similar to this:

   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. Create a Pod in the default namespace:

   security/example-baseline-pod.yaml

   apiVersion: v1 kind: Pod metadata:  name: nginx spec:  containers:  - image: nginx  name: nginx  ports:  - containerPort: 80 

   kubectl apply -f https://k8s.io/examples/security/example-baseline-pod.yaml 

   The pod is started normally, but the output includes a warning:

   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 

Clean up

Now delete the clusters which you created above by running the following command:

kind delete cluster --name psa-with-cluster-pss 

kind delete cluster --name psa-wo-cluster-pss 

What's next

• Run a shell script to perform all the preceding steps at once:
  1. Create a Pod Security Standards based cluster level Configuration
  2. Create a file to let API server consume this configuration
  3. Create a cluster that creates an API server with this configuration
  4. Set kubectl context to this new cluster
  5. Create a minimal pod yaml file
  6. Apply this file to create a Pod in the new cluster
• Pod Security Admission
• Pod Security Standards
• Apply Pod Security Standards at the namespace level