Jenkins – How to build a specific branch on GitHub

Jenkins – How to build a specific branch on GitHub. In this guide you are going to learn how to configure Jenkins to trigger build automatically once a change is made to a specific branch in GitHub.

By default if you configure CI/CD using Jenkins to build automatically once a commit is made, it triggers the build for commits made to any branch in a repository.

Prerequisites

• Install and configure Jenkins on Ubuntu.
• Setup Nginx reverse proxy for your Jenkins Installation.

Make sure you have the above mentioned prerequisites are completed.

Step 1: Install Generic Webhooks Trigger Plugin

Login to your Jenkins installation setup and navigate to Manage Jenkins >> Manage Plugins and click on the Available tab and install Generic Webhook Trigger Plugin.

Restart Jenkins to use the plugin.

Step 2: Setup GitHub Personal Access Token

Login to your GitHub account and go to your account Settings >> Developer Settings >> Personal access tokens.

Click Generate new token.

Enter a note in the Note field.

Select repo.

Click Generate token.

Now a new token will be visible for this one time.

Copy the generated token.

Step 3: Setup Webhooks in Github

Login to your GitHub account and go to the repository that is configured in Jenkins. Click on Settings >> Webhooks.

In the Payload URL enter the the url in the following format.

Replace JENKINS_URL with your own URL.

Replace YOUR_TOKEN with the personal access token you created in the previous step.

https://JENKINS_URL/generic-webhook-trigger/invoke?token=YOUR_TOKEN

In the Content type select application/json.

In the Which events choose Just the push event.

Click Add webhook.

Step 4: Configure Jenkins to build only specific branch

Once you have your Webhook created you can configure Jenkins to trigger build only if a push is made to the specific repository.

This configuration is for Freestyle Project in Jenkins.

Login to your Jenkins installation and go you your job and click configure.

In the Source Code Management section under Build Triggers check the Generic Webhook Trigger.

Click Add next to the Post content parameters.

Once a push is made, GitHub passes the branch name in the JSON format with the ref key.

The example payload will look something as shown below.

{
   "ref": "refs/heads/branch_name",
   "before": "5b6f5bfbb31d9d28f5655cs8753gae308ef392c5",
   "after": "0000000000000000000000000000000000000000",
   "repository": { 

...

In the Variable enter the name of the variable as ref.

In the Expression enter $.ref to match the key and choose the JSONPath format of payload.

In the Token field enter the personal access token you created before.

Next we can configure Optional Filter.

In the Expression field enter the branch name to match the key ref as shown below.

refs/heads/branch_name

In the Text field enter the variable name you assigned before as $ref.

Save the configuration.

Now you have configured your job to trigger the build only a push is made to a specific branch.

Conclusion

Now you have learned how to configure Jenkins to trigger build automatically if a push is made to the specific branch.

Thanks for your time. If you face any problem or any feedback, please leave a comment below.