Apply Pod Security Standards at the Cluster Level

Note

This tutorial applies only for new clusters.

Pod Security admission (PSA) is enabled by default in v1.23 and later, as it has graduated to beta. Pod Security is an admission controller that carries out checks against the Kubernetes Pod Security Standards when new pods are created. 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.

Before you begin

Install the following on your workstation:

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:

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

    The output is similar to this:

    1. Creating cluster "psa-wo-cluster-pss" ...
    2. ✓ Ensuring node image (kindest/node:v1.23.0) 🖼
    3. ✓ Preparing nodes 📦  
    4. ✓ Writing configuration 📜
    5. ✓ Starting control-plane 🕹️
    6. ✓ Installing CNI 🔌
    7. ✓ Installing StorageClass 💾
    8. Set kubectl context to "kind-psa-wo-cluster-pss"
    9. You can now use your cluster with:
    11. kubectl cluster-info --context kind-psa-wo-cluster-pss
    13. Thanks for using kind! 😊

  2. Set the kubectl context to the new cluster:

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

    The output is similar to this:

    1.  Kubernetes control plane is running at https://127.0.0.1:61350
    3. CoreDNS is running at https://127.0.0.1:61350/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy
    5. To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.

  3. Get a list of namespaces in the cluster:

    1. kubectl get ns

    The output is similar to this:

    1. NAME                 STATUS   AGE
    2. default              Active   9m30s
    3. kube-node-lease      Active   9m32s
    4. kube-public          Active   9m32s
    5. kube-system          Active   9m32s
    6. local-path-storage   Active   9m26s

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

    1. Privileged

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

    The output is similar to this:

    1. namespace/default labeled
    2. namespace/kube-node-lease labeled
    3. namespace/kube-public labeled
    4. namespace/kube-system labeled
    5. namespace/local-path-storage labeled

    1. Baseline

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

    The output is similar to this:

    1. namespace/default labeled
    2. namespace/kube-node-lease labeled
    3. namespace/kube-public labeled
    4. Warning: existing pods in namespace "kube-system" violate the new PodSecurity enforce level "baseline:latest"
    5. Warning: etcd-psa-wo-cluster-pss-control-plane (and 3 other pods): host namespaces, hostPath volumes
    6. Warning: kindnet-vzj42: non-default capabilities, host namespaces, hostPath volumes
    7. Warning: kube-proxy-m6hwf: host namespaces, hostPath volumes, privileged
    8. namespace/kube-system labeled
    9. namespace/local-path-storage labeled
    1. Restricted
    1.  kubectl label --dry-run=server --overwrite ns --all \
    2.  pod-security.kubernetes.io/enforce=restricted

    The output is similar to this:

    1. namespace/default labeled
    2. namespace/kube-node-lease labeled
    3. namespace/kube-public labeled
    4. Warning: existing pods in namespace "kube-system" violate the new PodSecurity enforce level "restricted:latest"
    5. Warning: coredns-7bb9c7b568-hsptc (and 1 other pod): unrestricted capabilities, runAsNonRoot != true, seccompProfile
    6. 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
    7. Warning: kindnet-vzj42: non-default capabilities, host namespaces, hostPath volumes, allowPrivilegeEscalation != false, unrestricted capabilities, restricted volume types, runAsNonRoot != true, seccompProfile
    8. Warning: kube-proxy-m6hwf: host namespaces, hostPath volumes, privileged, allowPrivilegeEscalation != false, unrestricted capabilities, restricted volume types, runAsNonRoot != true, seccompProfile
    9. namespace/kube-system labeled
    10. Warning: existing pods in namespace "local-path-storage" violate the new PodSecurity enforce level "restricted:latest"
    11. Warning: local-path-provisioner-d6d9f7ffc-lw9lh: allowPrivilegeEscalation != false, unrestricted capabilities, runAsNonRoot != true, seccompProfile
    12. 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:

    1. mkdir -p /tmp/pss
    2. cat <<EOF > /tmp/pss/cluster-level-pss.yaml 
    3. apiVersion: apiserver.config.k8s.io/v1
    4. kind: AdmissionConfiguration
    5. plugins:
    6. - name: PodSecurity
    7.   configuration:
    8.     apiVersion: pod-security.admission.config.k8s.io/v1beta1
    9.     kind: PodSecurityConfiguration
    10.     defaults:
    11.       enforce: "baseline"
    12.       enforce-version: "latest"
    13.       audit: "restricted"
    14.       audit-version: "latest"
    15.       warn: "restricted"
    16.       warn-version: "latest"
    17.     exemptions:
    18.       usernames: []
    19.       runtimeClasses: []
    20.       namespaces: [kube-system]
    21. EOF

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

    1. cat <<EOF > /tmp/pss/cluster-config.yaml 
    2. kind: Cluster
    3. apiVersion: kind.x-k8s.io/v1alpha4
    4. nodes:
    5. - role: control-plane
    6.   kubeadmConfigPatches:
    7.   - |
    8.     kind: ClusterConfiguration
    9.     apiServer:
    10.         extraArgs:
    11.           admission-control-config-file: /etc/config/cluster-level-pss.yaml
    12.         extraVolumes:
    13.           - name: accf
    14.             hostPath: /etc/config
    15.             mountPath: /etc/config
    16.             readOnly: false
    17.             pathType: "DirectoryOrCreate"
    18.   extraMounts:
    19.   - hostPath: /tmp/pss
    20.     containerPath: /etc/config
    21.     # optional: if set, the mount is read-only.
    22.     # default false
    23.     readOnly: false
    24.     # optional: if set, the mount needs SELinux relabeling.
    25.     # default false
    26.     selinuxRelabel: false
    27.     # optional: set propagation mode (None, HostToContainer or Bidirectional)
    28.     # see https://kubernetes.io/docs/concepts/storage/volumes/#mount-propagation
    29.     # default None
    30.     propagation: None
    31. 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:

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

    The output is similar to this:

    1.  Creating cluster "psa-with-cluster-pss" ...
    2.   ✓ Ensuring node image (kindest/node:v1.23.0) 🖼 
    3.   ✓ Preparing nodes 📦  
    4.   ✓ Writing configuration 📜 
    5.   ✓ Starting control-plane 🕹️ 
    6.   ✓ Installing CNI 🔌 
    7.   ✓ Installing StorageClass 💾 
    8.  Set kubectl context to "kind-psa-with-cluster-pss"
    9.  You can now use your cluster with:
    11.  kubectl cluster-info --context kind-psa-with-cluster-pss
    13.  Have a question, bug, or feature request? Let us know! https://kind.sigs.k8s.io/#community 🙂

  6. Point kubectl to the cluster

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

    The output is similar to this:

    1.  Kubernetes control plane is running at https://127.0.0.1:63855
    2.  CoreDNS is running at https://127.0.0.1:63855/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy
    4.  To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.

  7. Create the following Pod specification for a minimal configuration in the default namespace:

    1. cat <<EOF > /tmp/pss/nginx-pod.yaml
    2. apiVersion: v1
    3. kind: Pod
    4. metadata:
    5.   name: nginx
    6. spec:
    7.   containers:
    8.     - image: nginx
    9.       name: nginx
    10.       ports:
    11.         - containerPort: 80
    12. EOF

  8. Create the Pod in the cluster:

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

    The output is similar to this:

    1.  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")
    2.  pod/nginx created

Clean up

Run kind delete cluster --name psa-with-cluster-pss and kind delete cluster --name psa-wo-cluster-pss to delete the clusters you created.

What’s next