Measures

To enhance the security, resource management, and operational integrity of your Kubernetes cluster, follow these best practices for Admission Controllers:

Enable Key Admission Controllers for Security and Resource Management:

AlwaysPullImages:

This Admission Controller forces every pod to pull its image before starting, regardless of the image pull policy defined in the pod’s specification. This prevents the use of outdated or locally cached images, ensuring that the latest versions are always pulled from trusted registries.

Benefit: Ensures that pods always use up-to-date, secure images from the registry, reducing the risk of running compromised or outdated images.

PodSecurityPolicy (PSP):

The PodSecurityPolicy controller enforces security policies on pods by validating their security context. It helps define restrictions such as whether a pod can run as privileged, what capabilities it can request, and which volume types are allowed.

Benefit: Enhances the overall security posture of the cluster by enforcing pod-level security policies, preventing insecure configurations.

ResourceQuota:

This controller enforces resource quotas within namespaces, ensuring that resource usage does not exceed the defined limits for CPU, memory, storage, or other resources.

Benefit: Prevents resource exhaustion by limiting the resources each namespace can consume. This helps in managing resource allocation, avoiding DoS conditions, and ensuring fair resource distribution.

NamespaceExists:

The NamespaceExists controller ensures that resources can only be created in namespaces that exist. This prevents the creation of resources in incorrect or non-existent namespaces, helping maintain namespace integrity and preventing operational misconfigurations.

Benefit: Ensures consistency by allowing resources to be created only in valid namespaces, avoiding misconfigurations and potential security gaps.

Enable and Configure Admission Controllers in the API Server:

Admission Controllers can be enabled and configured in the API server using the --admission-control flag. For example:

kube-apiserver:

  ...

  - --admission-control=AlwaysPullImages,PodSecurityPolicy,ResourceQuota,NamespaceExists

Regularly Review and Update Admission Controllers:

As security and operational needs evolve, regularly review the Admission Controllers in use and enable additional controllers as needed. For example, new Kubernetes versions may introduce new controllers that provide enhanced functionality or security.

Monitoring and Auditing:

Continuously monitor the behavior of Admission Controllers and audit their effectiveness. Use tools like Kubernetes audit logs and policy enforcement solutions such as Open Policy Agent (OPA) to track and enforce Admission Controller configurations.

Example Workflow for Configuring Admission Controllers:

Assessment: Assess the operational and security requirements of your Kubernetes environment and identify which Admission Controllers are essential for your cluster.

Configuration: Add the necessary Admission Controllers (e.g., AlwaysPullImages, PodSecurityPolicy, ResourceQuota, NamespaceExists) to the API server configuration using the --admission-control flag.

Review: Regularly review and update the Admission Controllers in use to adapt to evolving security policies and cluster requirements.

Monitoring and Auditing: Implement continuous monitoring and auditing to ensure Admission Controllers are functioning as intended and enforcing policies consistently.

By enabling and configuring the appropriate Admission Controllers, you can enhance the security and resource management of your Kubernetes cluster, ensuring that only valid, secure, and policy-compliant requests are processed by the API server.