What is Continuous Integration?

Short answer

Continuous Integration (CI) is the practice of automatically building and testing code changes whenever they are committed to a shared repository. It catches integration errors early and ensures the codebase remains healthy.

How it works

Developers push code to a central repository. The CI server detects the change, checks out the code, installs dependencies, runs the build, executes tests, and reports results. If any step fails, the team is notified immediately.

Example

A typical CI pipeline:

stages:
  - build
  - test

build:
  script:
    - npm ci
    - npm run build

test:
  script:
    - npm test

Why it matters

CI reduces the cost of fixing bugs by catching them minutes after they are introduced. It encourages small, frequent commits and eliminates long-lived feature branches that are painful to merge.

Tips

• Keep builds fast; aim for under 10 minutes.
• Run tests in parallel where possible.
• Use feature branches and require CI to pass before merging.

Common issues

• Flaky tests undermine trust in CI.
• Slow builds discourage frequent commits.
• Environment differences between CI and production cause false confidence.