Jenkins is an open-source automation server primarily used for Continuous Integration (CI) and Continuous Delivery (CD) in software development. It helps automate various tasks in the software development lifecycle, such as building, testing, and deploying applications. Here's how it works:
Jenkins Server Jenkins runs on a server, which can be installed on a variety of operating systems (Linux, Windows, macOS). It has a web-based interface where you can configure Jenkins jobs, pipelines, and monitor the execution of these tasks.
Jobs A job in Jenkins is a single task or a series of tasks that Jenkins automates. Jobs could be anything like building code, running tests, or deploying software. You can define jobs through the web interface or by using configuration files like Jenkinsfile (a text file that defines the pipeline stages).
Pipelines Pipelines are a set of automated steps or stages that describe the process of building, testing, and deploying an application. A Jenkins Pipeline is typically defined in a Jenkinsfile and can be a Declarative Pipeline or a Scripted Pipeline. Pipelines define how the project is built, tested, and delivered through various environments (dev, test, production).
Source Code Management (SCM) Jenkins can be integrated with various source control repositories like Git, Subversion, etc. Jenkins pulls the latest code from the repository whenever a new build is triggered (manually or automatically, e.g., via a webhook from GitHub).
Build and Test Jenkins automates the build process (compiling code, creating artifacts) and testing process (running unit tests, integration tests) to ensure that the codebase is stable. After the build, Jenkins can also trigger additional steps like static code analysis or security scans.
Triggering Jobs Jenkins jobs can be triggered in several ways: Poll SCM: Jenkins periodically checks for changes in the source code repository and starts a build if changes are detected. Webhook: Many modern version control systems like GitHub can send a webhook to Jenkins to trigger a build when code is pushed to the repository. Scheduled Builds: You can schedule builds to run at specific times, such as nightly or weekly. Manual Triggers: Developers or administrators can manually trigger jobs from the Jenkins interface.
Agents/Nodes Jenkins can be scaled horizontally by using agents (also called slaves in earlier versions). Agents are machines that help Jenkins execute tasks. The main Jenkins server (Master) coordinates the execution of tasks, while agents can run the actual build processes. This allows for better load distribution and faster processing of builds.
Notifications and Reporting After each build or test, Jenkins provides feedback via the user interface, email, or integration with other tools like Slack or Microsoft Teams. Jenkins can also generate build reports and display test results, code coverage, and other metrics.
Plugins Jenkins has a robust ecosystem of plugins that extend its functionality. You can add plugins to integrate Jenkins with various tools and technologies, such as: Docker for containerized builds AWS for deployment Slack for notifications GitHub for source control Selenium for automated testing Summary Jenkins works by automating software development tasks through jobs and pipelines. It integrates with version control systems, triggers builds and tests, scales using agents, and provides feedback through reports and notifications. Through its extensive plugin ecosystem, Jenkins can be customized to support nearly any development workflow.
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