Note:In GitLab 8.3, Jenkins integration using theGitLab Hook Pluginwas deprecated in favor of theGitLab Plugin.The deprecated integration has been renamed to Jenkins CI (Deprecated) in theproject service settings. We may remove this in a future release and recommendusing the new \’Jenkins CI\’ project service instead which is described in thisdocument.

Overview

Jenkins is a great Continuous Integration tool, similar to our built-inGitLab CI.
GitLab\’s Jenkins integration allows you to trigger a Jenkins build when youpush code to a repository, or when a merge request is created. Additionally,it shows the pipeline status on merge requests widgets and on the project\’s home page.
Videos are also available on GitLab workflow with Jira issues and Jenkins pipelinesand Migrating from Jenkins to GitLab.

Use cases

• Suppose you are new to GitLab, and want to keep using Jenkins until you prepare your projects to build with GitLab CI/CD. You set up the integration between GitLab and Jenkins, then you migrate to GitLab CI later. While you organize yourself and your team to onboard GitLab, you keep your pipelines running with Jenkins, but view the results in your project\’s repository in GitLab.- Your team uses Jenkins Plugins for other proceedings, therefore, you opt for keep using Jenkins to build your apps. Show the results of your pipelines directly in GitLab.
  For a real use case, read the blog post Continuous integration: From Jenkins to GitLab using Docker.
  NOTE: Moving from a traditional CI plug-in to a single application for the entire software development lifecycle can decrease hours spent on maintaining toolchains by 10% or more.Visit the \’GitLab vs. Jenkins\’ comparison page to learn how our built-in CI compares to Jenkins.

Requirements

• Jenkins GitLab Plugin– Jenkins Git Plugin– Git clone access for Jenkins from the GitLab repository- GitLab API access to report build status

Configure GitLab users

Create a user or choose an existing user that Jenkins will use to interactthrough the GitLab API. This user will need to be a global Admin or addedas a member to each Group/Project. Developer permission is required for reportingbuild status. This is because a successful build status can trigger a mergewhen \’Merge when pipeline succeeds\’ feature is used. Some features of the GitLabPlugin may require additional privileges. For example, there is an option toaccept a merge request if the build is successful. Using this feature wouldrequire developer, maintainer or owner-level permission.
Copy the private API token from Profile Settings -> Account. You will need thiswhen configuring the Jenkins server later.

Configure the Jenkins server

Install Jenkins GitLab Pluginand Jenkins Git Plugin.
Go to Manage Jenkins -> Configure System and scroll down to the \’GitLab\’ section.Enter the GitLab server URL in the \’GitLab host URL\’ field and paste the API tokencopied earlier in the \’API Token\’ field.
For more information, see GitLab Plugin documentation about Jenkins-to-GitLab authentication

Configure a Jenkins project

Follow the GitLab Plugin documentation about Jenkins Job Configuration.
NOTE: Note:Be sure to include the steps about Build status configuration.The \’Publish build status to GitLab\’ post-build step is required to viewJenkins build status in GitLab Merge Requests.

Configure a GitLab project

Create a new GitLab project or choose an existing one. Then, go to Integrations ->Jenkins CI.
Check the \’Active\’ box. Select whether you want GitLab to trigger a buildon push, Merge Request creation, tag push, or any combination of these. Werecommend unchecking \’Merge Request events\’ unless you have a specific use-casethat requires re-building a commit when a merge request is created. With \’Pushevents\’ selected, GitLab will build the latest commit on each push and the buildstatus will be displayed in the merge request.
Enter the Jenkins URL and Project name. The project name should be URL-friendlywhere spaces are replaced with underscores. To be safe, copy the project namefrom the URL bar of your browser while viewing the Jenkins project.
Optionally, enter a username and password if your Jenkins server requiresauthentication.

Plugin functional overview

GitLab does not contain a database table listing commits. Commits are alwaysread from the repository directly. Therefore, it is not possible to retain thebuild status of a commit in GitLab. This is overcome by requesting buildinformation from the integrated CI tool. The CI tool is responsible for creatingand storing build status for Commits and Merge Requests.

Steps required to implement a similar integration

Note:All steps are implemented using AJAX requests on the merge request page.

1. In order to display the build status in a merge request you must create a project service in GitLab.1. Your project service will do a (JSON) query to a URL of the CI tool with the SHA1 of the commit.1. The project service builds this URL and payload based on project service settings and knowledge of the CI tool.1. The response is parsed to give a response in GitLab (success/failed/pending).
   ## Troubleshooting
   ### Error in merge requests – Could not connect to the CI server
   This integration relies on Jenkins reporting the build status back to GitLab viathe Commit Status API.
   The error \’Could not connect to the CI server\’ usually means that GitLab did notreceive a build status update via the API. Either Jenkins was not properlyconfigured or there was an error reporting the status via the API.
2. Configure the Jenkins server for GitLab API access1. Configure a Jenkins project, including the \’Publish build status to GitLab\’ post-build action.

https://docs.gitlab.com/ee/integration/jenkins.html

Jenkins-to-GitLab authentication

PLEASE NOTE: This auth configuration is only used for accessing the GitLab API for sending build status to GitLab. It is not used for cloning git repos. The credentials for cloning (usually SSH credentials) should be configured separately, in the git plugin.

This plugin can be configured to send build status messages to GitLab, which show up in the GitLab Merge Request UI. To enable this functionality:

1. Create a new user in GitLab
2. Give this user \’Developer\’ permissions on each repo you want Jenkins to send build status to
3. Log in or \’Impersonate\’ that user in GitLab, click the user\’s icon/avatar and choose Settings
4. Click on \’Access Tokens\’
5. Create a token named e.g. \’jenkins\’ with \’api\’ scope; expiration is optional
6. Copy the token immediately, it cannot be accessed after you leave this page
7. On the Global Configuration page in Jenkins, in the GitLab configuration section, supply the GitLab host URL, e.g. http://your.gitlab.server
8. Click the \’Add\’ button to add a credential, choose \’GitLab API token\’ as the kind of credential, and paste your GitLab user\’s API key into the \’API token\’ field
9. Click the \’Test Connection\’ button; it should succeed

https://github.com/jenkinsci/gitlab-plugin#jenkins-to-gitlab-authentication