Jenkins is the original open-source automation server, first released in 2011 as a fork of Hudson and now maintained by the CD Foundation. It is the workhorse of self-hosted continuous integration and delivery, running everywhere from a single Docker container to fleets of distributed agents orchestrating thousands of pipelines per day. Despite the rise of cloud-native CI services like GitHub Actions and CircleCI, Jenkins remains dominant in enterprises that require on-prem control, strict network isolation, or deep customization that hosted services cannot provide.
Pipelines in Jenkins are defined as code through Jenkinsfile — a Groovy-based DSL that supports declarative or scripted syntax. Workflows can spin up containers as agents, run matrix builds across operating systems and language versions, gate deployments on manual approval, and integrate with virtually any tool through the plugin ecosystem. With over 1,800 community plugins covering source control, build tools, cloud providers, secret managers, and notification channels, Jenkins can be wired into almost any release process. Configuration as Code (JCasC) lets teams version-control the entire Jenkins setup alongside their application code.
Jenkins is free and open source under the MIT license, with no usage limits — the cost is the infrastructure you run it on and the operator effort to keep plugins, agents, and the controller upgraded. CloudBees offers a commercial distribution with hardened security, enterprise support, and policy controls for organizations that want a vendor backstop. For teams already invested in self-hosted infrastructure, especially those with regulated workloads or air-gapped environments, Jenkins is still the most flexible CI/CD foundation available.
