Pod Security Policy (PSP) in Deep Dive into Kubernetes Security
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Pod Security Policy, or PSP, was a crucial admission controller in Kubernetes that enforced security constraints on Pod creation and updates. It acted as a gatekeeper, preventing the deployment of Pods with insecure configurations such as running as root, using privileged containers, or accessing host namespaces.
PSP worked as an admission controller in the Kubernetes API server workflow. When a user submitted a Pod creation request, the API server would intercept it and validate the Pod specification against configured PSP objects. The controller would check various security constraints including user and group IDs, capabilities, volume types, and host access permissions before either accepting or rejecting the Pod.
PSP enforced various security constraints to ensure Pod security. These included controlling user and group IDs to prevent running as root, blocking privileged containers, preventing privilege escalation, restricting access to host namespaces like hostNetwork and hostPID, limiting volume types, and managing Linux capabilities. Pods meeting these constraints would be accepted, while those violating them would be rejected.
PSP was deprecated in Kubernetes version 1.21 in 2021 and completely removed in version 1.25 in 2022. The removal was driven by several factors including its complex RBAC binding model, difficult management requirements, and widespread user confusion. The Kubernetes community recognized that better alternatives were needed to provide Pod security enforcement.
PSP has been replaced by better alternatives. Pod Security Admission, or PSA, is now built into Kubernetes and provides simpler configuration with namespace-level enforcement. External policy engines like Open Policy Agent with Gatekeeper, Falco, and Kyverno offer more flexible policy management. These successors provide better usability, more intuitive configuration, and enhanced policy capabilities compared to the deprecated PSP system.