Pod Security Admission

The Kubernetes Pod Security Standards define different isolation levels for Pods. These standards let you define how you want to restrict the behavior of pods in a clear, consistent fashion.

As a Beta feature, Kubernetes offers a built-in Pod Security admission controller, the successor to PodSecurityPolicies. Pod security restrictions are applied at the namespace level when pods are created.

Enabling the PodSecurity admission plugin

In v1.23, the PodSecurity feature gate is a Beta feature and is enabled by default.

In v1.22, the PodSecurity feature gate is an Alpha feature and must be enabled in kube-apiserver in order to use the built-in admission plugin.

--feature-gates="...,PodSecurity=true"

Alternative: installing the PodSecurity admission webhook

For environments where the built-in PodSecurity admission plugin cannot be used, either because the cluster is older than v1.22, or the PodSecurity feature cannot be enabled, the PodSecurity admission logic is also available as a Beta validating admission webhook.

A pre-built container image, certificate generation scripts, and example manifests are available at https://git.k8s.io/pod-security-admission/webhook.

To install:

git clone https://github.com/kubernetes/pod-security-admission.git
cd pod-security-admission/webhook
make certs
kubectl apply -k .

Pod Security levels

Pod Security admission places requirements on a Pod's Security Context and other related fields according to the three levels defined by the Pod Security Standards: privileged, baseline, and restricted. Refer to the Pod Security Standards page for an in-depth look at those requirements.

Pod Security Admission labels for namespaces

Once the feature is enabled or the webhook is installed, you can configure namespaces to define the admission control mode you want to use for pod security in each namespace. Kubernetes defines a set of labels that you can set to define which of the predefined Pod Security Standard levels you want to use for a namespace. The label you select defines what action the control plane takes if a potential violation is detected:

A namespace can configure any or all modes, or even set a different level for different modes.

For each mode, there are two labels that determine the policy used:

# The per-mode level label indicates which policy level to apply for the mode.
#
# MODE must be one of `enforce`, `audit`, or `warn`.
# LEVEL must be one of `privileged`, `baseline`, or `restricted`.
pod-security.kubernetes.io/<MODE>: <LEVEL>

# Optional: per-mode version label that can be used to pin the policy to the
# version that shipped with a given Kubernetes minor version (for example v1.23).
#
# MODE must be one of `enforce`, `audit`, or `warn`.
# VERSION must be a valid Kubernetes minor version, or `latest`.
pod-security.kubernetes.io/<MODE>-version: <VERSION>

Check out Enforce Pod Security Standards with Namespace Labels to see example usage.

Workload resources and Pod templates

Pods are often created indirectly, by creating a workload object such as a Deployment or Job. The workload object defines a Pod template and a controller for the workload resource creates Pods based on that template. To help catch violations early, both the audit and warning modes are applied to the workload resources. However, enforce mode is not applied to workload resources, only to the resulting pod objects.

Exemptions

You can define exemptions from pod security enforcement in order to allow the creation of pods that would have otherwise been prohibited due to the policy associated with a given namespace. Exemptions can be statically configured in the Admission Controller configuration.

Exemptions must be explicitly enumerated. Requests meeting exemption criteria are ignored by the Admission Controller (all enforce, audit and warn behaviors are skipped). Exemption dimensions include:

• Usernames: requests from users with an exempt authenticated (or impersonated) username are ignored.
• RuntimeClassNames: pods and workload resources specifying an exempt runtime class name are ignored.
• Namespaces: pods and workload resources in an exempt namespace are ignored.

Updates to the following pod fields are exempt from policy checks, meaning that if a pod update request only changes these fields, it will not be denied even if the pod is in violation of the current policy level:

• Any metadata updates except changes to the seccomp or AppArmor annotations:
  • seccomp.security.alpha.kubernetes.io/pod (deprecated)
  • container.seccomp.security.alpha.kubernetes.io/* (deprecated)
  • container.apparmor.security.beta.kubernetes.io/*
• Valid updates to .spec.activeDeadlineSeconds
• Valid updates to .spec.tolerations

What's next

• Pod Security Standards
• Enforcing Pod Security Standards
• Enforce Pod Security Standards by Configuring the Built-in Admission Controller
• Enforce Pod Security Standards with Namespace Labels
• Migrate from PodSecurityPolicy to the Built-In PodSecurity Admission Controller