Jenkins, GitHub Actions, GitLab CI and other orchestrators that run your pipelines.
Jenkins, GitHub Actions, GitLab CI and other orchestrators that run your pipelines.
Lesson outline
CI tools watch for changes (for example, Git pushes, pull requests, or schedule triggers) and run your pipeline definition: build, test, package, and deploy.
They provide logs, artifacts, and status checks so you can see whether a change is safe to merge or deploy. In DevOps terms, they automate the “factory line” that code moves through.
Jenkins is highly customizable and plugin‑rich but you manage the servers. GitHub Actions and GitLab CI are hosted and integrate tightly with their platforms. Pick based on ecosystem, control needs, and maintenance budget.
Modern CI tools encourage you to define pipelines in code (Jenkinsfile, GitHub Actions YAML, GitLab CI YAML). This makes reviews, rollbacks, and experimentation safer.
Keep pipeline definitions in the same repo as the application where possible so changes to code and pipeline travel together.
If you start with ad‑hoc jobs in a UI, migrate toward pipelines-as-code: create a pipeline definition that mirrors your manual steps, then gradually simplify and standardize.
When reading DevOps case studies, this is often how teams move from fragile, one‑off jobs to reliable, repeatable pipelines shared across teams.
DevOps and platform engineering interviews: expect to explain the trade-offs between self-hosted (Jenkins) and hosted CI (GitHub Actions, GitLab CI), and demonstrate knowledge of pipelines as code.
Common questions:
Strong answer: Explaining pipelines-as-code and why it matters (reviewability, rollback). Discussing secret management (Jenkins credentials store, GitHub Actions secrets, Vault integration). Mentioning agent/runner resource planning and cost considerations.
Red flags: Describing CI pipelines as shell scripts in a UI. Not knowing what a Jenkinsfile or YAML pipeline definition is. Storing secrets in plaintext in pipeline configuration.
Quick check · Jenkins and CI tools
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💡 Analogy
A CI tool is a traffic controller for your code changes. Developers are cars pulling up to the intersection (the repository). The CI tool's job is to inspect each car (run tests, linting, security scans), approve the safe ones to proceed (merge, deploy), and direct the unsafe ones back to the garage (fail the build, notify the developer). A Jenkins master is the traffic control tower — if it goes down, all traffic stops. Pipelines as code are the traffic control rules written in a manual — if the tower is rebuilt, the rules are immediately restored from the manual.
⚡ Core Idea
CI tools do not make your code better — they make the cost of discovering problems earlier very low. A bug caught in CI costs minutes to fix; the same bug caught in production costs hours or days. The ROI of CI is the difference between those two costs, multiplied by the frequency of bugs.
🎯 Why It Matters
Every modern engineering team uses CI. Understanding CI tools at the "pipelines as code" and "secret management" level — not just "I pressed Run" — distinguishes engineers who can own and improve CI infrastructure from those who just consume it.
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