Kubernetes Admission Controllers for DevSecOps Workflows

 

A four-panel comic titled "Kubernetes Admission Controllers for DevSecOps Workflows." Panel 1: An engineer explains to a colleague, “Admission Controllers check requests before they go through!” Panel 2: A screen displays a “REJECTED” deployment, as another character says, “It blocked an unverified image!” Panel 3: Two engineers look at code with policy annotations and say, “Auto-inject security defaults.” Panel 4: The team smiles with thumbs-up, saying, “Policies enforced before deploy!”

Kubernetes Admission Controllers for DevSecOps Workflows

Modern DevSecOps pipelines require continuous enforcement of security and compliance—not just during build and test, but also during deployment.

Kubernetes Admission Controllers play a critical role in enforcing these policies at the API server level before resources are committed to the cluster.

By intercepting incoming requests and applying validation, mutation, or rejection logic, Admission Controllers ensure your deployments adhere to security best practices and organizational rules.

This guide explores how they work, how to implement them, and which open-source tools can extend their capabilities.

📌 Table of Contents

🔍 What Are Kubernetes Admission Controllers?

Admission Controllers are plugins that intercept Kubernetes API requests before they’re persisted to etcd.

They act as gatekeepers that can validate, mutate, or outright reject resource definitions based on custom logic or policy sets.

These controllers work in tandem with role-based access control (RBAC), pod security standards (PSS), and auditing tools.

🔄 Types: Validating vs Mutating

ValidatingAdmissionWebhook: Rejects resources that don’t meet security or compliance criteria.

MutatingAdmissionWebhook: Automatically modifies incoming resource specs to enforce defaults (e.g., inject labels, configure sidecars).

Both can be chained for complex policy enforcement at scale.

🔐 Benefits for DevSecOps

✔ Enforce zero-trust deployment rules before containers run.

✔ Prevent image pulls from unverified registries.

✔ Ensure resource limits and securityContext are always set.

✔ Automate configuration injection like environment variables or secrets.

🛠️ Popular Tools and Policy Engines

1. OPA/Gatekeeper: Use Rego policies to define and enforce custom rules.

2. Kyverno: A native Kubernetes policy engine with easy YAML syntax.

3. Kubewarden: Use WebAssembly to enforce high-speed, language-agnostic policies.

4. K-Rail: Lightweight admission controller focused on best practices.

5. Conftest: Integrates policy-as-code testing with admission logic.

📋 Implementation Tips & Best Practices

✔ Start in audit mode to avoid breaking deployments.

✔ Scope policies to specific namespaces or labels.

✔ Use pre-built policy libraries and templates for faster rollout.

✔ Continuously test policies in CI/CD pipelines before production push.

🌐 Resources to Learn More About Admission Controllers

Automated Auditing for Kubernetes Resources

SOC 2 Controls with Admission Policy

CMDB-Synced Admission Control Rules

Admission Controllers for Private K8s

Encryption Enforcement via Admission Controllers

Use these resources to secure and standardize your DevSecOps deployment lifecycle in Kubernetes clusters.

Keywords: Kubernetes Admission Controllers, DevSecOps, Policy Enforcement, Gatekeeper, Kyverno