Webhook triggers from GitHub/GitLab in Jenkins - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

How does a webhook trigger Jenkins from GitHub?

Which statement best describes how a webhook triggers a Jenkins job from GitHub?

A GitHub sends an HTTP POST request to Jenkins when an event occurs, and Jenkins starts the job based on that request.

B Jenkins polls GitHub every minute to check for new commits and triggers the job if changes are found.

C GitHub pushes the entire repository to Jenkins, which then runs the job automatically.

D Jenkins sends a request to GitHub to start the webhook when a build is needed.

💡 Hint

Think about who initiates the communication when code changes happen.

GitHub webhooks send an HTTP POST request to Jenkins when a specified event happens, such as a push. Jenkins listens for this request and triggers the job accordingly.

💻 Command Output

intermediate

Jenkins webhook payload validation

What will Jenkins log show if it receives a webhook payload from GitLab with an invalid secret token?

Jenkins

Started by GitLab push webhook.
Secret token does not match. Ignoring the request.

A Started by GitLab push webhook. Secret token does not match. Ignoring the request.

B Build started successfully for the push event.

C Error: Unable to parse webhook payload.

D Webhook received but no matching job found.

💡 Hint

Check what happens when the secret token is wrong.

Jenkins verifies the secret token sent with the webhook. If it does not match the configured token, Jenkins ignores the request and logs this message.

❓ Configuration

advanced

Configuring Jenkins to trigger on GitHub pull request events

Which Jenkinsfile snippet correctly configures a pipeline to trigger only on GitHub pull request events using a webhook?

Jenkins

pipeline {
  agent any
  triggers {
    githubPullRequest()
  }
  stages {
    stage('Build') {
      steps {
        echo 'Building pull request...'
      }
    }
  }
}

A triggers { pollSCM('H/5 * * * *') }

B triggers { githubPullRequest() }

C triggers { cron('H/5 * * * *') }

D triggers { githubPush() }

💡 Hint

Look for the trigger that listens specifically to pull requests.

The githubPullRequest() trigger listens for pull request events from GitHub webhooks and triggers the pipeline accordingly.

❓ Troubleshoot

advanced

Why does Jenkins not trigger on GitLab webhook despite correct URL?

You configured a GitLab webhook to trigger Jenkins on push events. The webhook URL is correct, but Jenkins does not start the job. What is the most likely cause?

A The Jenkins server is offline and cannot receive webhooks.

B The GitLab webhook is set to trigger on merge requests instead of push events.

C The secret token configured in Jenkins does not match the token set in GitLab webhook settings.

D The Jenkins job is disabled.

💡 Hint

Check the security settings that validate webhook authenticity.

If the secret token in Jenkins and GitLab webhook settings do not match, Jenkins will ignore the webhook even if the URL is correct.

🔀 Workflow

expert

Order of steps for setting up GitHub webhook to trigger Jenkins pipeline

Arrange the steps in the correct order to set up a GitHub webhook that triggers a Jenkins pipeline on push events.

A 1,3,2,4

B 1,2,3,4

C 3,2,1,4

D 3,1,2,4

💡 Hint

Think about setting security before adding webhook and testing.

First generate and configure the secret token in Jenkins and GitHub (3), then create the Jenkins job (1), add the webhook in GitHub (2), and finally test by pushing code (4).