You are viewing documentation for Kubernetes version: v1.23
Kubernetes v1.23 documentation is no longer actively maintained. The version you are currently viewing is a static snapshot. For up-to-date documentation, see the latest version.
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:
-
Create a cluster with no Pod Security Standards applied:
kind create cluster --name psa-wo-cluster-pss --image kindest/node:v1.23.0
The output is similar to this:
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! 😊
-
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'.
-
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
-
Use
--dry-run=server
to understand what happens when different Pod Security Standards are applied:- Privileged
kubectl label --dry-run=server --overwrite ns --all \ pod-security.kubernetes.io/enforce=privileged
The output is similar to this:
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
The output is similar to this:
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
The output is similar to this:
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
- Privileged
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 inenforce
mode.restricted
standard inwarn
andaudit
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:
-
Based on the risk posture applied to a cluster, a stricter Pod Security Standard like
restricted
might be a better choice. -
Exempting the
kube-system
namespace allows pods to run asprivileged
in this namespace. For real world use, the Kubernetes project strongly recommends that you apply strict RBAC policies that limit access tokube-system
, following the principle of least privilege. To implement the preceding standards, do the following: -
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/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
-
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. -
Create a cluster that uses Pod Security Admission to apply these Pod Security Standards:
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:
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 🙂
-
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'.
-
Create the following Pod specification for a minimal configuration in the default namespace:
cat <<EOF > /tmp/pss/nginx-pod.yaml apiVersion: v1 kind: Pod metadata: name: nginx spec: containers: - image: nginx name: nginx ports: - containerPort: 80 EOF
-
Create the Pod in the cluster:
kubectl apply -f /tmp/pss/nginx-pod.yaml
The output is similar to this:
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
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
- Run a
shell script
to perform all the preceding steps at once:
- Create a Pod Security Standards based cluster level Configuration
- Create a file to let API server consumes this configuration
- Create a cluster that creates an API server with this configuration
- Set kubectl context to this new cluster
- Create a minimal pod yaml file
- 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