Suppose you want to run a Jenkins pipeline any time commits are pushed to GitHub. Easy, right? In abstract, yes. But, when you have additional requirements, it is not so easy.
At the outset, GitHub provides a webhook that allows you to receive push notifications. That is, any time someone pushes a commit to GitHub, a GitHub sends an HTTP POST event is sent to the indicated URL, with the details of the push in JSON format. Jenkins has Git and GitHub plugins that make it really easy to build pipelines any time there are pushes to GitHub.
First of all, a few words of warning are worth stating in relation to how you setup triggers in your pipeline. If you have the multibranch pipeline plugin, you can view the configuration for each branch, but you cannot modify it. Instead, if there are any rules you want to enforce on particular branches, you write those in your Jenkinsfile in the pipeline syntax. The particular rule that you might be interested in configuring is branch triggering. Unfortunately, as it turns out, for pipeline branch strategy, you cannot assign webhook triggers to individual branches.
20190916/DuckDuckGo jenkins modify branch settings
20190916/https://stackoverflow.com/questions/45322742/jenkins-edit-config-in-multi-branch-pipeline
20190916/DuckDuckGo jenkins multi-branch pipeline
20190916/https://wiki.jenkins.io/display/JENKINS/Pipeline+Multibranch+Plugin
20190916/https://jenkins.io/doc/book/pipeline/syntax
20190916/https://jenkins.io/doc/book/pipeline/syntax/#triggers
20190916/https://jenkins.io/blog/2015/12/03/pipeline-as-code-with-multibranch-workflows-in-jenkins/
20190916/DuckDuckGo trigger jenkins multibranch from script
20190916/Google jenkins start multibranch build from script
20190916/https://stackoverflow.com/questions/46140233/github-webhooks-triggered-globally-instead-of-per-branch
If you simply want GitHub to send Jenkins push notifications via a webhook for any time there are repository changes to any GitHub repository, you simply configure GitHub to hit a single API push endpoint in Jenkins, which is managed by the GitHub plugin. The default API URL looks something like this.
https://jenkins.yournetwork.net/github-webhook/
Another thing to watch out for is documentation about getting information on user API tokens to Jenkins. The methods of getting this information via the “Manage Jenkins” page do not work with the AD/LDAP integration plugin, so don’t be going down this path if you have your Jenkins server setup with the AD/LDAP plugin. Rather, you should go to your user settings by clicking on your username at the upper righthand corner of the web API, then go to “Configure.” You will be able to generate API tokens for your user account here.
20190916/DuckDuckGo jenkins multibranch build trigger token
20190916/https://stackoverflow.com/questions/42817169/jenkins-trigger-builds-remotely-authentication-token-option-missing
20190916/https://wiki.jenkins.io/display/JENKINS/Authenticating-scripted-clients
So, all that being said, first of all, how do you run a Jenkins build by having a script hit a REST API endpoint? Simple, set up something like this:
https://USERNAME:token@jenkins.yournetwork.net/job/PROJECT/job/REPO/job/BRANCH/build
This starts a build without any parameters.
20190916/DuckDuckGo jenkins api to start build job
20190916/https://stackoverflow.com/questions/8512807/calling-a-jenkins-build-from-outside-jenkins
Now, here’s where the trick and complication comes into play. We need to solve is to have a way to use webhooks, but one where only notifications for a particular branches are used to start a particular job. You can setup GitHub webhooks for a particular repository and point them to a Jenkins job, but the problem here is that a push to any branch will start your Jenkins job. But, let’s start by looking into that anyways.
20190904/DuckDuckkGo github jenkins trigger
20190904/https://www.fourkitchens.com/blog/article/trigger-jenkins-builds-pushing-github/
20190904/DuckDuckkGo jenkins build strategies
20190904/https://stackoverflow.com/questions/53765094/how-to-configure-basic-branch-build-strategies-using-job-dsl
20190916/https://wiki.jenkins.io/display/JENKINS/GitHub+Plugin#GitHubPlugin-ManualMode
20190916/https://developer.github.com/enterprise/2.15/webhooks/
20190916/https://developer.github.com/enterprise/2.15/webhooks/#events
20190916/https://developer.github.com/enterprise/2.15/v3/activity/events/types/#pushevent
GitHub’s push webhook exposes a variety of useful information that can then be processed to determine if a Jenkins build should be started for a particular branch. What we can do is construct an intermediate Jenkins job that directly recieves the webhook, processes the JSON input, and determines if there is a branch match for starting the target Jenkins job.
20190916/DuckDuckGo jenkins job extract json from post request
20190916/DuckDuckGo jenkins build job extract json from post request
20190916/https://stackoverflow.com/questions/38041557/build-jenkins-job-with-parameters-from-curl-http-post
The way this works is that you tie the GitHub webhook configuration to
a Jenkins Build Job with parameters POST REST API, and configure the
webhook to use payload type application/x-www-form-encoded instead
of application/json.
https://USERNAME:token@jenkins.yournetwork.net/job/PROJECT/job/REPO/job/BRANCH/buildWithParameters?token=TOKEN
20190923/DuckDuckGo jenkins build with parameters artibtrary json payload
20190923/https://stackoverflow.com/questions/31407332/how-to-process-a-github-webhook-payload-in-jenkins
The whole body of the JSON payload that GitHub submits to the webhook
will be provided in the parameter named payload. You can then parse
that out using this Groovy JSON parser library.
20190916/http://docs.groovy-lang.org/latest/html/gapi/groovy/json/JsonSlurper.html