As Pipeline is adopted for more and more projects in an organization, common patterns are likely to emerge. Oftentimes it is useful to share parts of Pipelines between various projects to reduce redundancies and keep code "DRY" [1].
Pipeline has support for creating "Shared Libraries" which can be defined in external source control repositories and loaded into existing Pipelines.
A Shared Library is defined with a name, a source code retrieval method such as by SCM, and optionally a default version. The name should be a short identifier as it will be used in scripts.
The version could be anything understood by that SCM; for example, branches, tags, and commit hashes all work for Git. You may also declare whether scripts need to explicitly request that library (detailed below), or if it is present by default. Furthermore, if you specify a version in Jenkins configuration, you can block scripts from selecting a different version.
The best way to specify the SCM is using an SCM plugin which has been specifically updated to support a new API for checking out an arbitrary named version (Modern SCM option). As of this writing, the latest versions of the Git and Subversion plugins support this mode; others should follow.
If your SCM plugin has not been integrated, you may select Legacy SCM and
pick anything offered. In this case, you need to include
${library.yourLibName.version}
somewhere in the configuration of the SCM, so
that during checkout the plugin will expand this variable to select the desired
version. For example, for Subversion, you can set the Repository URL to
svnserver/project/${library.yourLibName.version}
and then use
versions such as trunk
or branches/dev
or tags/1.0
.
The directory structure of a Shared Library repository is as follows:
(root)
+- src # Groovy source files
| +- org
| +- foo
| +- Bar.groovy # for org.foo.Bar class
+- vars
| +- foo.groovy # for global 'foo' variable
| +- foo.txt # help for 'foo' variable
+- resources # resource files (external libraries only)
| +- org
| +- foo
| +- bar.json # static helper data for org.foo.Bar
The src
directory should look like standard Java source directory structure.
This directory is added to the classpath when executing Pipelines.
The vars
directory hosts script files that are exposed as a variable in Pipelines. The name of the file is the name of the variable in the Pipeline.
So if you had a file called vars/log.groovy
with a function like def info(message)…
in it, you can access this function like log.info "hello world"
in the Pipeline. You can put as many functions as you like inside this file. Read on below for more examples and options.
The basename of each .groovy
file should be a Groovy (~ Java) identifier, conventionally camelCased
.
The matching .txt
, if present, can contain documentation, processed through the system’s configured markup formatter (so may really be HTML, Markdown, etc., though the .txt
extension is required). This documentation will only be visible on the Global Variable Reference pages that are accessed from the navigation sidebar of Pipeline jobs that import the shared library. In addition, those jobs must run successfully once before the shared library documentation will be generated.
The Groovy source files in these directories get the same “CPS transformation” as in Scripted Pipeline.
A resources
directory allows the libraryResource
step to be used from an external library to load associated non-Groovy files.
Currently this feature is not supported for internal libraries.
Other directories under the root are reserved for future enhancements.
There are several places where Shared Libraries can be defined, depending on the use-case. Manage Jenkins » System » Global Pipeline Libraries as many libraries as necessary can be configured.
Since these libraries will be globally usable, any Pipeline in the system can utilize functionality implemented in these libraries.
These libraries are considered "trusted:" they can run any methods in Java, Groovy, Jenkins internal APIs, Jenkins plugins, or third-party libraries. This allows you to define libraries which encapsulate individually unsafe APIs in a higher-level wrapper safe for use from any Pipeline. Beware that anyone able to push commits to this SCM repository could obtain unlimited access to Jenkins. You need the Overall/RunScripts permission to configure these libraries (normally this will be granted to Jenkins administrators).
Any Folder created can have Shared Libraries associated with it. This mechanism allows scoping of specific libraries to all the Pipelines inside of the folder or subfolder.
Folder-based libraries are not considered "trusted:" they run in the Groovy sandbox just like typical Pipelines.
Other plugins may add ways of defining libraries on the fly. For example, the
Pipeline: GitHub Groovy Libraries plugin
allows a script to use an untrusted library
named like github.com/someorg/somerepo
without any additional configuration. In
this case, the specified GitHub repository would be loaded, from the master
branch, using an anonymous checkout.
Shared Libraries marked Load implicitly allows Pipelines to immediately use
classes or global variables defined by any such libraries. To access other
shared libraries, the Jenkinsfile
needs to use the @Library
annotation,
specifying the library’s name:
@Library('my-shared-library') _
/* Using a version specifier, such as branch, tag, etc */
@Library('my-shared-library@1.0') _
/* Accessing multiple libraries with one statement */
@Library(['my-shared-library', 'otherlib@abc1234']) _
The annotation can be anywhere in the script where an annotation is permitted
by Groovy. When referring to class libraries (with src/
directories),
conventionally the annotation goes on an import
statement:
@Library('somelib')
import com.mycorp.pipeline.somelib.UsefulClass
For Shared Libraries which only define Global Variables ( It is not recommended to |
Libraries are resolved and loaded during compilation of the script, before it starts executing. This allows the Groovy compiler to understand the meaning of symbols used in static type checking, and permits them to be used in type declarations in the script, for example:
@Library('somelib')
import com.mycorp.pipeline.somelib.Helper
int useSomeLib(Helper helper) {
helper.prepare()
return helper.count()
}
echo useSomeLib(new Helper('some text'))
Global Variables however, are resolved at runtime.
This video reviews using resource files from a Shared Library. A link to the example repository used is also provided in the video description.
As of version 2.7 of the Pipeline: Shared Groovy Libraries plugin,
there is a new option for loading (non-implicit) libraries in a script:
a library
step that loads a library dynamically, at any time during the build.
If you are only interested in using global variables/functions (from the vars/
directory),
the syntax is quite simple:
library 'my-shared-library'
Thereafter, any global variables from that library will be accessible to the script.
Using classes from the src/
directory is also possible, but trickier.
Whereas the @Library
annotation prepares the “classpath” of the script prior to compilation,
by the time a library
step is encountered the script has already been compiled.
Therefore you cannot import
or otherwise “statically” refer to types from the library.
However you may use library classes dynamically (without type checking),
accessing them by fully-qualified name from the return value of the library
step.
static
methods can be invoked using a Java-like syntax:
library('my-shared-library').com.mycorp.pipeline.Utils.someStaticMethod()
You can also access static
fields, and call constructors as if they were static
methods named new
:
def useSomeLib(helper) { // dynamic: cannot declare as Helper
helper.prepare()
return helper.count()
}
def lib = library('my-shared-library').com.mycorp.pipeline // preselect the package
echo useSomeLib(lib.Helper.new(lib.Constants.SOME_TEXT))
The "Default version" for a configured Shared Library is used when "Load
implicitly" is checked, or if a Pipeline references the library only by name,
for example @Library('my-shared-library') _
. If a "Default version" is not
defined, the Pipeline must specify a version, for example
@Library('my-shared-library@master') _
.
If "Allow default version to be overridden" is enabled in the Shared Library’s
configuration, a @Library
annotation may also override a default version
defined for the library. This also allows a library with "Load implicitly" to
be loaded from a different version if necessary.
When using the library
step you may also specify a version:
library 'my-shared-library@master'
Since this is a regular step, that version could be computed rather than a constant as with the annotation; for example:
library "my-shared-library@$BRANCH_NAME"
would load a library using the same SCM branch as the multibranch Jenkinsfile
.
As another example, you could pick a library by parameter:
properties([parameters([string(name: 'LIB_VERSION', defaultValue: 'master')])])
library "my-shared-library@${params.LIB_VERSION}"
Note that the library
step may not be used to override the version of an implicitly loaded library.
It is already loaded by the time the script starts, and a library of a given name may not be loaded twice.
The best way to specify the SCM is using an SCM plugin which has been specifically updated to support a new API for checking out an arbitrary named version (Modern SCM option). As of this writing, the latest versions of the Git and Subversion plugins support this mode.
SCM plugins which have not yet been updated to support the newer features
required by Shared Libraries, may still be used via the Legacy SCM option.
In this case, include ${library.yourlibrarynamehere.version}
wherever a
branch/tag/ref may be configured for that particular SCM plugin. This ensures
that during checkout of the library’s source code, the SCM plugin will expand
this variable to checkout the appropriate version of the library.
If you only specify a library name (optionally with version after @
) in the library
step,
Jenkins will look for a preconfigured library of that name.
(Or in the case of a github.com/owner/repo
automatic library it will load that.)
But you may also specify the retrieval method dynamically, in which case there is no need for the library to have been predefined in Jenkins. Here is an example:
library identifier: 'custom-lib@master', retriever: modernSCM(
[$class: 'GitSCMSource',
remote: 'git@git.mycorp.com:my-jenkins-utils.git',
credentialsId: 'my-private-key'])
It is best to refer to Pipeline Syntax for the precise syntax for your SCM.
Note that the library version must be specified in these cases.
At the base level, any valid Groovy code is okay for use. Different data structures, utility methods, etc, such as:
// src/org/foo/Point.groovy
package org.foo
// point in 3D space
class Point {
float x,y,z
}
Library classes cannot directly call steps such as sh
or git
.
They can however implement methods, outside of the scope of an enclosing
class, which in turn invoke Pipeline steps, for example:
// src/org/foo/Zot.groovy
package org.foo
def checkOutFrom(repo) {
git url: "git@github.com:jenkinsci/${repo}"
}
return this
Which can then be called from a Scripted Pipeline:
def z = new org.foo.Zot()
z.checkOutFrom(repo)
This approach has limitations; for example, it prevents the declaration of a superclass.
Alternately, a set of steps
can be passed explicitly using this
to a library class, in a
constructor, or just one method:
package org.foo
class Utilities implements Serializable {
def steps
Utilities(steps) {this.steps = steps}
def mvn(args) {
steps.sh "${steps.tool 'Maven'}/bin/mvn -o ${args}"
}
}
When saving state on classes, such as above, the class must implement the
Serializable
interface. This ensures that a Pipeline using the class, as seen
in the example below, can properly suspend and resume in Jenkins.
@Library('utils') import org.foo.Utilities
def utils = new Utilities(this)
node {
utils.mvn 'clean package'
}
If the library needs to access global variables, such as env
, those should be
explicitly passed into the library classes, or methods, in a similar manner.
Instead of passing numerous variables from the Scripted Pipeline into a library,
package org.foo
class Utilities {
static def mvn(script, args) {
script.sh "${script.tool 'Maven'}/bin/mvn -s ${script.env.HOME}/jenkins.xml -o ${args}"
}
}
The above example shows the script being passed in to one static
method,
invoked from a Scripted Pipeline as follows:
@Library('utils') import static org.foo.Utilities.*
node {
mvn this, 'clean package'
}
Internally, scripts in the vars
directory are instantiated on-demand as
singletons. This allows multiple methods to be defined in a
single .groovy
file for convenience. For example:
def info(message) {
echo "INFO: ${message}"
}
def warning(message) {
echo "WARNING: ${message}"
}
@Library('utils') _
log.info 'Starting'
log.warning 'Nothing to do!'
Declarative Pipeline does not allow method calls on objects outside "script" blocks.
(JENKINS-42360).
The method calls above would need to be put inside a script
directive:
@Library('utils') _
pipeline {
agent none
stages {
stage ('Example') {
steps {
// log.info 'Starting' (1)
script { (2)
log.info 'Starting'
log.warning 'Nothing to do!'
}
}
}
}
}
1 | This method call would fail because it is outside a script directive. |
2 | script directive required to access global variables in Declarative Pipeline. |
A variable defined in a shared library will only show up in Global Variables Reference (under Pipeline Syntax) after Jenkins loads and uses that library as part of a successful Pipeline run. |
Avoid preserving state in global variables
All global variables defined in a Shared Library should be stateless, i.e. they should act as collections of functions. If your pipeline tried to store some state in global variables, this state would be lost in case of Jenkins controller restart. Use a static class or instantiate a local variable of a class instead. |
Though using fields for global variables is discouraged as per above, it is possible to define fields and use them as read-only. To define a field you need to use an annotation:
@groovy.transform.Field
def yourField = "YourConstantValue"
def yourFunction....
Shared Libraries can also define global variables which behave similarly to
built-in steps, such as sh
or git
. Global variables defined in Shared
Libraries must be named with all lowercase or "camelCased" in order to be
loaded properly by Pipeline.
[2]
For example, to define sayHello
, the file vars/sayHello.groovy
should be created and should implement a call
method. The call
method
allows the global variable to be invoked in a manner similar to a step:
// vars/sayHello.groovy
def call(String name = 'human') {
// Any valid steps can be called from this code, just like in other
// Scripted Pipeline
echo "Hello, ${name}."
}
The Pipeline would then be able to reference and invoke this variable:
sayHello 'Joe'
sayHello() /* invoke with default arguments */
If called with a block, the call
method will receive a
Closure
.
The type should be defined explicitly to clarify the intent of the step, for
example:
// vars/windows.groovy
def call(Closure body) {
node('windows') {
body()
}
}
The Pipeline can then use this variable like any built-in step which accepts a block:
windows {
bat "cmd /?"
}
If you have a lot of Pipelines that are mostly similar, the global
variable mechanism provides a handy tool to build a higher-level DSL
that captures the similarity. For example, all Jenkins plugins are built and
tested in the same way, so we might write a step named
buildPlugin
:
// vars/buildPlugin.groovy
def call(Map config) {
node {
git url: "https://github.com/jenkinsci/${config.name}-plugin.git"
sh 'mvn install'
mail to: '...', subject: "${config.name} plugin build", body: '...'
}
}
Assuming the script has either been loaded as a
Global Shared Library or as a
Folder-level Shared Library
the resulting Jenkinsfile
will be dramatically simpler:
buildPlugin name: 'git'
There is also a “builder pattern” trick using Groovy’s Closure.DELEGATE_FIRST
,
which permits Jenkinsfile
to look slightly more like a configuration file than a program,
but this is more complex and error-prone and is not recommended.
While possible, accessing third-party libraries using |
It is possible to use third-party Java libraries, typically found in
Maven Central,
from trusted library code using the @Grab
annotation. Refer to the
Grape documentation
for details, but simply put:
@Grab('org.apache.commons:commons-math3:3.4.1')
import org.apache.commons.math3.primes.Primes
void parallelize(int count) {
if (!Primes.isPrime(count)) {
error "${count} was not prime"
}
// …
}
Third-party libraries are cached by default in ~/.groovy/grapes/
on the
Jenkins controller.
External libraries may load adjunct files from a resources/
directory using
the libraryResource
step. The argument is a relative pathname, akin to Java
resource loading:
def request = libraryResource 'com/mycorp/pipeline/somelib/request.json'
The file is loaded as a string, suitable for passing to certain APIs or saving
to a workspace using writeFile
.
It is advisable to use an unique package structure so you do not accidentally conflict with another library.
If you notice a mistake in a build using an untrusted library, simply click the Replay link to try editing one or more of its source files, and see if the resulting build behaves as expected. Once you are satisfied with the result, follow the diff link from the build’s status page, and apply the diff to the library repository and commit.
(Even if the version requested for the library was a branch, rather than a fixed version like a tag, replayed builds will use the exact same revision as the original build: library sources will not be checked out again.)
Replay is not currently supported for trusted libraries. Modifying resource files is also not currently supported during Replay.
Starting with Declarative 1.2, released in late September, 2017, you can define Declarative Pipelines in your shared libraries as well. Here’s an example, which will execute a different Declarative Pipeline depending on whether the build number is odd or even:
// vars/evenOrOdd.groovy
def call(int buildNumber) {
if (buildNumber % 2 == 0) {
pipeline {
agent any
stages {
stage('Even Stage') {
steps {
echo "The build number is even"
}
}
}
}
} else {
pipeline {
agent any
stages {
stage('Odd Stage') {
steps {
echo "The build number is odd"
}
}
}
}
}
}
// Jenkinsfile
@Library('my-shared-library') _
evenOrOdd(currentBuild.getNumber())
Only entire pipeline
s can be defined in shared libraries as of this time.
This can only be done in vars/*.groovy
, and only in a call
method. Only one
Declarative Pipeline can be executed in a single build, and if you attempt to
execute a second one, your build will fail as a result.
By adding @Library('my-shared-library@pull/<your-pr-number>/head') _
at the top of a library consumer Jenkinsfile, you can test your pipeline library pull request changes in situ if your pipeline library is hosted on GitHub and the SCM configuration for the pipeline library uses GitHub.
Refer to the pull request or merge request branch naming convention for other providers like Assembla, Bitbucket, Gitea, GitLab, and Tuleap.
Take, for example, a change to the global ci.jenkins.io shared pipeline, which has its source code stored at github.com/jenkins-infra/pipeline-library/.
Let’s say you’re writing a new feature and opened a pull request on the pipeline library, number 123
.
By opening a pull request on the dedicated jenkins-infra-test-plugin
test repository with the following content, you’ll be able to check your changes on ci.jenkins.io:
--- jenkins-infra-test-plugin/Jenkinsfile
+++ jenkins-infra-test-plugin/Jenkinsfile
@@ -1,3 +1,4 @@
+ @Library('pipeline-library@pull/123/head') _
buildPlugin(
useContainerAgent: true,
configurations: [
[platform: 'linux', jdk: 17],
[platform: 'windows', jdk: 11],
])
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