200-901 Application Deployment and Security Practice Question
A CI/CD pipeline using GitHub Actions needs to build a Docker image and push it to Docker Hub. Which event trigger should be used to run the workflow only when code is pushed to the main branch?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
on: push: branches: [ main ]
The 'push' event with branch filter triggers on pushes to main. 'pull_request' triggers on PRs, 'release' on releases, 'workflow_dispatch' manual trigger.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
on: workflow_dispatch
Why it's wrong here
workflow_dispatch triggers a manual run from the GitHub UI or API, so pushes to main never start the build. It tempts for release or hotfix pipelines needing human initiation, but this scenario requires automatic execution on push, which the push event with a branch filter provides.
- ✓
on: push: branches: [ main ]
Why this is correct
The push trigger with a branches filter limited to main runs the workflow only on commits pushed to that branch, satisfying the stated condition. Pull request events and pushes to other branches will not trigger the build-and-push job.
- ✗
on: release: types: [ published ]
Why it's wrong here
A release trigger fires only when a GitHub release is published, not on code pushes, so the image would not build at commit time. It tempts because publishing a release is a natural point to ship a tagged image, but the stem specifies running on pushes to main, which requires the push event.
- ✗
on: pull_request: branches: [ main ]
Why it's wrong here
A pull_request trigger fires on PR activity against main, not on direct pushes, so the build would never run when commits land on main. It is tempting because it genuinely gates pull requests targeting main, which is the right trigger when validation must occur before merge rather than after.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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