Kubernetes Agents

Kubernetes agents allow Jenkins to run builds as ephemeral pods inside a Kubernetes cluster. This is the most scalable and cloud-native Jenkins execution model.

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What Is a Kubernetes Agent?

A Kubernetes agent is a temporary pod created on demand for a Jenkins build.

Key traits:

• One pod per build (usually)
• Destroyed after completion
• Fully isolated environment
• Defined via pod templates

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Why Kubernetes Agents Are Used

Kubernetes agents solve problems such as:

• Static agent saturation
• Tool version conflicts
• Inefficient scaling
• Costly idle infrastructure

They enable true horizontal auto-scaling.

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High-Level Architecture

1. Jenkins controller runs outside or inside Kubernetes
2. Kubernetes plugin requests a pod
3. Kubernetes schedules the pod
4. Pipeline runs inside the pod
5. Pod is destroyed after completion

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Pod Templates

Pod templates define:

• Containers
• Images
• Resources (CPU / memory)
• Volumes
• Environment variables

They act as agent blueprints.

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Basic Declarative Example

pipeline {
  agent {
    kubernetes {
      label 'maven-agent'
      defaultContainer 'maven'
      yaml '''
apiVersion: v1
kind: Pod
spec:
  containers:
  - name: maven
    image: maven:3.9-eclipse-temurin-17
    command:
    - cat
    tty: true
'''
    }
  }
  stages {
    stage('Build') {
      steps {
        sh 'mvn clean package'
      }
    }
  }
}

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Multi-Container Pods

Common pattern:

• One container for build
• One for tools (Docker, scanners)

Example:

• maven
• docker
• kubectl

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Resource Management

Always define:

• CPU requests/limits
• Memory requests/limits

This prevents:

• Node exhaustion
• Unstable clusters

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Kubernetes Agents vs Docker Agents

Aspect	Docker Agents	Kubernetes Agents
Isolation	Container	Pod (multi-container)
Scaling	Limited	Auto-scaled
Infra	VM-based	Cloud-native
Cost efficiency	Medium	High
Enterprise adoption	Medium	High

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Common Mistakes

• No resource limits
• Large pod templates
• Too many containers per pod
• Running Jenkins controller with build permissions

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Best Practices

• Use small, purpose-built images
• One pod per pipeline
• Define resource requests and limits
• Separate prod and non-prod clusters
• Restrict pod permissions

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Security Considerations

• Pods execute untrusted code
• Use Kubernetes RBAC
• Avoid privileged containers
• Isolate namespaces

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Interview Focus Areas

• Docker agents vs Kubernetes agents
• Why pods are preferred over containers
• Pod templates and lifecycle