What is CI?

CI (Continuous Integration) is a practice in which developers frequently and regularly integrate their changes into a shared repository, and every change is automatically checked.

In simpler terms: every commit is automatically checked so it does not break the project.

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#What CI is about

The main idea of CI:

• developers commit code often
• changes reach the shared repository right away
• checks run automatically

Bugs are found earlier, not right before a release.

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#What CI usually does

When a new commit / PR / tag appears, CI:

1. downloads the code
2. builds the project
3. runs linters
4. runs the tests
5. reports the result (success / failure)

If something fails, the code should not move further.

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#When CI runs

CI can run:

• on every push
• when a Pull Request is opened
• when a PR is updated
• when a tag is created (a release)

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#Examples of CI systems

In practice these are:

• GitHub Actions
• GitLab CI/CD
• Jenkins
• CircleCI
• Travis CI

(it is important to know the idea, not a specific tool)

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#How CI differs from "no CI"

Without CI:

• bugs are found manually
• problems surface right before a release
• complex merges and "overnight fixes"

With CI:

• fast feedback
• fewer conflicts
• a stable main codebase

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#CI and the Git workflow

CI is especially important for:

• Feature Branch Workflow
• Gitflow
• Trunk-Based Development

In all cases, CI is a guardian of quality.

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#Short answer for an interview

CI is the practice of continuous integration, where every code change is automatically built and checked with tests, to find errors early and keep the project stable.