Jenkins Concepts
External
Internal
Artifact
An artifact is an immutable file generated during a build or a pipeline run. The artifact is archived onto the master for later retrieval by users. Usage of artifacts can be tracked globally across multiple pipeline or projects via the artifact's fingerprint. Jenkins provides API to manage artifacts (archiveArtifacts, etc.)
Node
A machine which is part of the Jenkins environment and capable of executing pipelines or projects. Both the masters and agents are considered to be nodes. To view the list of nodes, go to Manage Jenkins → Manage Nodes. The master(s) and the worker nodes are listed there.
Master
A master is a central, coordinating process that stores configuration, loads plugins, and renders the various user interfaces for Jenkins.
Agent
An agent, also known as a "build agent", is the runtime that executes the build. An agent can be a host, virtual machine or a container. Agents to execute a build may be selected with a label expression, specified in the job configuration. The agent connects to a master and executes tasks when directed by master.
Label
Agents are grouped using labels, which is user-defined text indicating similar functionality or capability. Also see:
Agent Cloud
A cloud is a system configuration that provides dynamic agent provisioning and allocations. Example of clouds are Amazon EC2 cloud, Amazon EC2 Container Service cloud, Azure VM agents, etc.
Amazon EC2 Cloud
The cloud of agents consists of Amazon EC2 instances, provisioned and managed by the "Amazon EC2" plugin. For more details, see:
Amazon EC2 Container Service Cloud
The cloud of agents consists of ECS containers, deployed in an ECS cluster. The agent cloud is managed by the (incorrectly named) "Amazon EC2 Container Service" plugin. For more details, see:
Amazon SpotFleet
Azure VM Agents
Worker
Equivalent with agent, the master needs workers to execute specific parts of a build pipeline.
Docker Plugin Agent
Executor
An executor is a slot for execution of work defined by a pipeline or project on a node. A node may have zero or more executors configured which corresponds to how many concurrent projects or pipelines are able to execute on that node. An executor can be thought as a single “process ID” or as the basic unit of resource that Jenkins executes on the node (in most cases the node is an agent) to run a build. An executor allows a build to run on an agent.
Slave
Items
pipelines, projects and folders are items.
Folder
pipelines and projects can be organized in folders, which is an organizational container for items, similar to folders on a filesystem.
Project (Freestyle Project)
A project is a user-configured description of work which Jenkins should perform, such as building a piece of software, etc. Projects are a replacement for the deprecated term "job".
GitHub Repository
An item that watches a GitHub repository and triggers actions on repository changes. Not found under "New Items" in the UI. A new one can be created by copying an existing GitHub Repository by going to New Item → Copy from .
Job
A job is a deprecated term, synonymous with Project. A single execution of a job results in a build.
Jobs can be created from the UI and they show up on the dashboard, in the main table. A job state is maintained in $JENKINS_HOME/jobs/<job-name>. The job directory contains a config.xml and a "builds" subdirectory, which contains build state. The state include links to "lastFailedBuild", "lastStableBuild", "lastSuccessfulBuild", "lastUnstableBuild" and "lastUnsuccessfulBuild".
A job can be configured with Jenkins -> job -> Configure.
A job's configuration contains the following:
- General Configuration
- Source Code Management configuration
- Build Triggers
- Build Environment
- Build definition - usually a shell command.
- Post-build actions.
Each job has its own security context.
Build
A build is the result of a single execution of a project (job). The build belongs to the project (job).
Publisher
A publisher is part of a build that publishes reports, sends notifications, etc. after the completion of all configured steps.
Pipeline
A user-defined model of software continuous delivery pipeline.
Pipeline Overview
A Jenkins pipeline is a suite of plugins that implement a continuous delivery pipeline. A pipeline orchestrates long-running activities that can span multiple build agents. Pipelines are expressed in Jenkins via the Pipeline DSL syntax (see below). The definition is written into a Jenkinsfile, or declared in the Jenkins UI. The pipeline code defines the entire build process, which typically includes stages for building the application, testing it and delivering it. An indented rendering of the pipeline execution is available by navigating to a build then picking "Pipeline Steps" from the left menu. A graphic rendering is available by picking "Open Blue Ocean" from the same menu. Pipelines are formerly known as workflows.
When integrated with OpenShift, the Jenkins Pipeline functionality provides the engine for OpenShift Pipeline builds. More details about OpenShift Jenkins pipeline are available here OpenShift Jenkins Pipelines.
Jenkinsfile
Jenkinsfile contain the definition of the pipeline. It is usually committed in the project source code repository - this makes the CD pipeline to be treated as part of the application to be versioned and reviewed like any other code. A Jenkinsfile can be written with two types of syntax: declarative (newer and recommended) and scripted.
Pipeline Node
A node is a machine. It is part of the Jenkins environment and it is capable of executing a pipeline. More details about Jenkins node are available in the "Node" section.
Stage
A stage is part of pipeline, used for defining a conceptually distinct subset of tasks performed through the pipeline (e.g. "Build", "Test", "Deploy").
Parallel Stage
Step
A step is a single task, that defines what Jenkins should do do at a particular point in time - a step in the process. Steps can be implemented as Groovy classes.
Pipeline Syntax, Writing a Jenkins Pipeline
Pipeline Execution
Pipeline Types
(Simple) Pipeline
Multibranch Pipeline
A set of pipeline projects according to detected branches in an SCM repository.
Multibranch Pipeline with Defaults
Extends the Multibranch pipeline plugin.
Trigger
A trigger is a criterion for triggering a new pipeline run or a build.
Downstream Pipeline/Project
A downstream pipeline or project is an pipeline/project that is triggered as part of the execution of a separate pipeline or project.
Upstream Pipeline/Project
An upstream pipeline or project triggers downstream pipeline or project as part of its execution.
View
Workspace
A workspace is a disposable directory on the file system of a node where work can be done by a pipeline or project. Workspaces are typically left in place after a build or pipeline run completes unless specific workspace cleanup policies have been put in place on the master. Workloads running on a slave node (via the node wrapper) get a fresh/empty workspace directory upon entry into the node wrapper. This may require using (S3-based) stash/unstash for large directories that need to be made available for slave node execution.
Build Environment
Distributed Build
Core
The core (jenkins.war) is the primary Jenkins application that provides the basic web UI, configuration and foundation upon which plugins can be built.
Plugin
A plugin is an extension to Jenkins functionality provided separately from Jenkins core. The list of installed plugins can be obtained on the console Jenkins -> Manage Jenkins -> Manage Plugins -> Installed.
Interesting Jenkins Plugins
- Task Scanner https://wiki.jenkins.io/pages/viewpage.action?pageId=2916549
- Docker
- Credentials
- Amazon EC2
- Amazon EC2 Container Service
Server Administration Concepts
Instance State
A Jenkins instance state consists of the following:
- The WAR file
- Plugins.
- Settings
- Build logs
- Artifacts archives
- Jobs
- Various temporary files associated with running the jobs, including repository clones: "jenkins_home/workspace/test-build/.git/..."
Everything mentioned above is stored under $JENKINS_HOME. It is sufficient to archive this directory to make a back up of the instance. Similarly, restoring the data is just replacing the contents of the JENKINS_HOME directory from a back up.
The WAR file is stored under ${JENKINS_HOME}/war. The location can be overridden with --webroot=<new-location>. The WAR is expanded during the startup sequence.
The plugins are stored under ${JENKINS_HOME}/plugins. The location can be overridden with --pluginroot =<new-location>.