> ## Documentation Index > Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt > Use this file to discover all available pages before exploring further. # Introduction to Jenkins > Jenkins is an open-source automation server that powers continuous integration and delivery, automating software pipelines from building to deploying applications. Jenkins is an open-source automation server that powers continuous integration and delivery (CI/CD). It automates your software pipeline—from building and testing to deploying applications—every time you push code. By integrating with popular tools like Git, Docker, and Kubernetes, Jenkins helps teams deliver high-quality software faster and with fewer manual steps. Jenkins supports over 1,800 plugins, making it easy to connect with version control systems, build tools, testing frameworks, and cloud providers. ## How Jenkins Works 1. **Trigger**\ A developer pushes code changes to a Git repository (e.g., GitHub, GitLab, Bitbucket). 2. **Detection**\ Jenkins polls the repository or listens for webhooks. 3. **Checkout & Build**\ The server clones the latest code, compiles it, and runs unit tests. 4. **Test & Report**\ If tests fail, Jenkins notifies the team via email, Slack, or other channels. 5. **Deploy**\ On success, Jenkins can package the artifact into a Docker image and deploy it to a Kubernetes cluster or EC2 instance. 6. **Feedback**\ Build and deployment statuses are displayed in the Jenkins UI and communicated back to the team. ![The image illustrates how Jenkins works in a CI/CD pipeline, showing the process from a developer's commit through Git, Jenkins' build and compile steps, and potential outcomes like errors or successful deployment using Docker and Kubernetes.](https://kodekloud.com/kk-media/image/upload/v1752870585/notes-assets/images/Certified-Jenkins-Engineer-Introduction-to-Jenkins/jenkins-ci-cd-pipeline-diagram.jpg) ## Core Concepts | Concept | Description | Example | | ----------------- | ----------------------------------------------------------------------------------------------------------------- | ------------------------------------------------ | | Job | A task definition for building, testing, or deploying code. Each run is a **build**, tracked with status history. | Compile a Java project or run a shell script. | | Freestyle Project | A GUI-based job type that lets you drag-and-drop build steps and post-build actions. | Combine Maven build, JUnit tests, and archiving. | | Pipeline | A Groovy-based script in a `Jenkinsfile` that defines multi-stage workflows as code. | `pipeline { stages { stage('Test') { ... }}}` | | Stage | A logical block within a pipeline (e.g., Build, Test, Deploy) that visualizes progress. | `stage('Deploy') { steps { ... } }` | | Node | The machine where Jenkins executes tasks. A **controller** orchestrates, and **agents** run jobs concurrently. | On-premise VM or Kubernetes pod. | | Plugin | An extension to integrate external tools or add functionality. | Git, Docker, Slack, AWS, Azure, etc. | ![The image explains Jenkins core concepts, including "Jobs," "Builds," and "Freestyle Project," alongside an illustration of the Jenkins mascot.](https://kodekloud.com/kk-media/image/upload/v1752870586/notes-assets/images/Certified-Jenkins-Engineer-Introduction-to-Jenkins/jenkins-core-concepts-jobs-builds.jpg) ![The image explains Jenkins core concepts, including stages, nodes, and plugins, with a cartoon character illustration.](https://kodekloud.com/kk-media/image/upload/v1752870587/notes-assets/images/Certified-Jenkins-Engineer-Introduction-to-Jenkins/jenkins-core-concepts-illustration.jpg) ## Pros and Cons ### Pros * Free and open-source with no licensing fees. * Huge plugin ecosystem for SCM, containers, cloud, and testing. * **Pipeline as Code**: Version-controlled `Jenkinsfile` for reproducible builds. * Customizable with Groovy scripts and shared libraries. * Scalable through distributed agents and cloud-based executors. * Rich reporting: parallel builds, artifacts, test results, and notifications. ### Cons * The UI and configuration options can be complex for new users. * Requires regular maintenance—core updates and plugin compatibility checks. * A single server may become a bottleneck; additional agents are needed for heavy workloads. * Security is user-managed: choose trusted plugins, apply patches, and enforce role-based access. * Unlike hosted solutions (e.g., [GitHub Actions](https://github.com/features/actions), [GitLab CI/CD](https://docs.gitlab.com/ee/ci/)), you handle hosting and scalability. Ensure you follow security best practices: upgrade Jenkins regularly, limit plugin installations, and configure proper access controls. ![The image presents a comparison of pros and cons, with the pros including features like being open source and customizable, and the cons highlighting issues like a steeper learning curve and security concerns.](https://kodekloud.com/kk-media/image/upload/v1752870587/notes-assets/images/Certified-Jenkins-Engineer-Introduction-to-Jenkins/pros-cons-comparison-open-source.jpg) *** ## Further Reading & References * [Jenkins Official Documentation](https://www.jenkins.io/doc/) * [Jenkins Pipeline Syntax](https://www.jenkins.io/doc/book/pipeline/syntax/) * [Continuous Integration with Jenkins](https://www.jenkins.io/solutions/ci/) * [Docker Hub](https://hub.docker.com/) * [Kubernetes Documentation](https://kubernetes.io/docs/) * [Terraform Registry](https://registry.terraform.io/)