Jenkins · DevOps & CI/CD Deep Dive

Anatomy

The Building Blocks

Controller — the Jenkins server (web UI, scheduler, config). Single point of failure unless you cluster it.
Agents — workers that actually run jobs; can be VMs, Docker, Kubernetes pods (via the K8s plugin).
Pipeline — a Jenkinsfile in the repo, written in Groovy DSL (declarative or scripted).
Stages & steps — declarative pipelines have named stages with steps {} inside.
Shared libraries — Groovy libraries loaded across pipelines for DRY.
Plugins — Git, GitHub, Slack, Kubernetes, Blue Ocean (newer UI), and 1,800 more.

Why It Endures

You own everything. No SaaS minute caps, no egress charges, no third-party reading your code.
Plugin coverage for everything from VMware to mainframes to embedded toolchains.
Distributed builds across heterogeneous agents — Linux x86, Windows, ARM, macOS — out of the box.
Pipeline as code via Jenkinsfile, lives next to the source.
Active LTS line with security backports.

Tradeoffs

Operational burden. Patching the controller, plugin upgrades, agent fleet, JVM tuning — somebody owns it.
Plugin sprawl is a security risk. Each plugin is code with controller-level access; CVEs are constant.
Groovy is a learning curve. Especially scripted pipelines and shared libraries.
UX is dated. Blue Ocean helps, but Jenkins still feels like 2012 next to Actions or Buildkite.
Single-controller bottleneck. Running thousands of pipelines per day usually means JCasC + many controllers (Jenkins X / CloudBees CI).

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