Inside Jenkins: Architecture, Internals & Power Hacks

Ideal for: DevOps engineers, CI/CD architects, and release managers.

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## 🧠 Session Goals

• Understand Jenkins core architecture
• Learn how pipelines are executed internally
• Explore master-agent mechanics
• Deep-dive into performance tuning, security, and plugin ecosystem

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### 🧱 1. Jenkins Architecture Deep Dive (15 mins)

✅ Topics:

• Jenkins Master (controller) vs Agents (nodes)
• How builds are distributed and executed
• Internal flow of a job: `queue → executor → workspace`
• Role of `jenkins.war`, `WEB-INF`, `/var/jenkins_home`

📊 Visuals:

• Diagram: Request flow (Git push → Jenkins Webhook → Build)
• Diagram: Controller ↔ Agent ↔ SCM ↔ Artifact Repo

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### 🧬 2. Pipeline Execution Internals (20 mins)

✅ Topics:

• Scripted vs Declarative pipeline (DSL parsing explained)
• Execution engine: CPS (Continuation Passing Style)
• Why Jenkins uses Groovy sandbox
• How Jenkins suspends/resumes builds (durable-task plugin)
• What’s happening in `.jenkins/workspace` and `.jenkins/jobs/*`

💡 Bonus:

• Show real file structure of a Jenkins job
• View `build.xml`, `nextBuildNumber`, `log`, etc.

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### ⚙️ 3. Jenkins Agents & Executors (15 mins)

✅ Topics:

• Agent launch methods: SSH, JNLP, Docker, Kubernetes
• How Jenkins maintains agent heartbeats
• Executors: What happens under the hood
• How Jenkins handles workspace allocation, node labels

📊 Demo Ideas:

• Connect and disconnect an agent live
• Simulate a build on a remote agent

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### 🚀 4. Plugin Ecosystem & Lifecycles (10 mins)

✅ Topics:

• How plugins are loaded (`.hpi` files, dependency injection)
• Plugin classloaders and extension points
• Safe restart & plugin reload (vs restart)
• Writing a simple plugin (brief concept + repo link)

💡 Mention:

• Must-know plugins: `Pipeline`, `BlueOcean`, `Credentials`, `Matrix Authorization`

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### 🔐 5. Security & Performance (15 mins)

✅ Topics:

• Role-based strategy vs Matrix-based security
• Script approval flows in sandboxed pipelines
• Jenkins internal security hardening (XSS, CSRF, Secret Key store)
• Performance tuning:
• GC optimization
• JVM tuning for large-scale Jenkins
• Parallelization tips (`parallel` block, agents on demand)

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### 🛠️ 6. Debugging Jenkins (10 mins)

✅ Topics:

• Jenkins logs (`jenkins.log`, `hudson.model.*`)
• Troubleshooting stuck pipelines
• Memory leaks (heap dumps, GC logs)
• Using `Script Console` (Manage Jenkins → Console)

💻 Live Example:

• Run a Groovy script to clean up old jobs or list all current builds.

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## 🧩 7. Wrap-up + Q&A (5 mins)

• Recap key takeaways
• Share cheat sheet / Jenkins war file internals
• Share GitHub repo with pipeline templates and Groovy scripts

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## 🔧 Optional Demos (can be interwoven)

• Live pipeline walk-through
• Agent scaling with Docker or K8s
• Use Jenkins Script Console to query or mutate data

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## 💾 Bonus Resources (share post-session)

• Jenkins Internals repo: [Your custom GitHub link]
• Groovy pipeline DSL cheatsheet
• Jenkinsfile best practices (with `when`, `post`, `parallel`)
• JVM tuning config for Jenkins