Build triggers (poll SCM, webhook, timer) in Jenkins - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this Jenkinsfile snippet with a poll SCM trigger?

Given this Jenkinsfile snippet, what will Jenkins do?

pipeline {
  triggers {
    pollSCM('H/15 * * * *')
  }
  stages {
    stage('Build') {
      steps {
        echo 'Building...'
      }
    }
  }
}

A Jenkins polls the source code repository every 15 minutes and triggers a build if changes are detected.

B Jenkins triggers a build every 15 minutes regardless of source code changes.

C Jenkins triggers a build only once when the pipeline is first created.

D Jenkins triggers a build every 15 seconds regardless of source code changes.

💡 Hint

Poll SCM means Jenkins checks the source code for changes on a schedule.

The pollSCM('H/15 * * * *') trigger tells Jenkins to check the source code repository every 15 minutes. It only triggers a build if it finds new changes.

🧠 Conceptual

intermediate

Which build trigger uses a webhook to start a Jenkins build?

Choose the build trigger type that starts a Jenkins build immediately when a source code change is pushed.

A Timer trigger

B Webhook trigger

C Poll SCM trigger

D Manual trigger

💡 Hint

Think about which trigger reacts instantly to external events.

A webhook trigger listens for events from the source code system and starts a build immediately when a change is pushed.

❓ Configuration

advanced

Identify the correct cron syntax for a Jenkins timer trigger to run daily at 2:30 AM

Which of the following cron expressions correctly schedules a Jenkins timer trigger to run every day at 2:30 AM?

A 2 30 * * *

B 30 02 * * 1-5

C 30 2 * * *

D 0 2 30 * *

💡 Hint

Cron format is: minute hour day-of-month month day-of-week

The correct cron expression is 30 2 * * * which means at minute 30, hour 2, every day.

❓ Troubleshoot

advanced

Why does a Jenkins job with poll SCM trigger never start a build?

A Jenkins job has a poll SCM trigger set to check every 10 minutes, but no builds start even after code changes. What is the most likely reason?

A The Jenkins server cannot access the source code repository to detect changes.

B The poll SCM trigger syntax is incorrect and causes a syntax error.

C The timer trigger is overriding the poll SCM trigger.

D The webhook is disabled, so builds cannot start.

💡 Hint

Think about network or permission issues that prevent Jenkins from checking the repository.

If Jenkins cannot reach the source code repository, it cannot detect changes and will not trigger builds even if poll SCM is configured.

✅ Best Practice

expert

Which build trigger strategy is best for minimizing unnecessary builds in a busy team?

Your team pushes code frequently. You want to minimize unnecessary Jenkins builds while ensuring fast feedback on changes. Which trigger strategy is best?

A Use manual triggers only to control builds.

B Use poll SCM every minute to catch changes quickly.

C Use a timer trigger to build every hour regardless of changes.

D Use webhook triggers to start builds immediately on push events.

💡 Hint

Consider which trigger reacts instantly but only when needed.

Webhook triggers start builds immediately only when code is pushed, avoiding unnecessary builds and providing fast feedback.