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Marko Anastasov
Marko Anastasov

Posted on • Originally published at

Continuous Integration Explained

Continuous integration enables iterative software development, reduces risks from defects and makes developers highly productive.

What is Continuous Integration?

Continuous integration (CI) is a software development practice in which developers merge their changes to the main branch many times per day. Each merge triggers an automated code build and test sequence, which ideally runs in less than 10 minutes. A successful CI build may lead to further stages of continuous delivery.

If a build fails, the CI system blocks it from progressing to further stages. The team receives a report and repairs the build quickly, typically within minutes.

All competitive technology companies today practice continuous integration. By working in small iterations, the software development process becomes predictable and reliable. Developers can iteratively build new features. Product managers can bring the right products to market, faster. Developers can fix bugs quickly and usually discover them before they even reach users.

Continuous integration requires all developers who work on a project to commit to it. Results need to be transparently available to all team members and build status reported to developers when they are changing the code. In case the main code branch fails to build or pass tests, an alert usually goes out to the entire development team who should take immediate action to get it back to a "green" state.

Why do we need Continuous Integration?

In business, especially in new product development, usually we can't figure everything up front. Taking smaller steps helps us estimate more accurately and validate more frequently. A shorter feedback loop means having more iterations. And it’s the number of iterations, not the number of hours invested, that drives learning.

For software development teams, working in long feedback loops is risky, as it increases the likelihood of errors and the amount of work needed to integrate changes into a working version software.

Small, controlled changes are safe to happen often. And by automating all integration steps, developers avoid repetitive work and human error. Instead of having people decide when and how to run tests, a CI tool monitors the central code repository and runs all automated tests on every commit. Based on the total result of tests, it either accepts or rejects the code commit.

Extension with Continuous Delivery

Once we automatically build and test our software, it gets easier to release it. Thus Continuous Integration is often extended with Continuous Delivery, a process in which code changes are also automatically prepared for a release (CI/CD).

In a fine-tuned CI/CD process, all code changes are being deployed to a staging environment, a production environment, or both after the CI stage has been completed.

Continuous delivery can be a fully automated workflow. In that case, it's usually referred to as Continuous Deployment. Or, it can be partially automated with manual steps at critical points. What's common in both scenarios is that developers always have a release artifact from the CI stage that has gone through a standardized test process and is ready to be deployed.

CI and CD pipeline

CI and CD are often represented as a pipeline, where new code enters on one end, flows through a series of stages (build, test, staging, production), and published as a new production release to end users on the other end.

Each stage of the CI/CD pipeline is a logical unit in the delivery process. Developers usually divide each unit into a series of subunits that run sequentially or in parallel.

ci/cd pipeline

I shared a more detailed post on CI/CD pipelines here on

Prerequisites for doing Continuous Integration

The basic prerequisites for implementing continuous integration include:

  • Automating builds;
  • Automating testing;
  • More frequent commits to a single source code repository, and
  • Providing visibility of the process and real-time access to CI status to the team.

Teams that don't practice CI yet should take small steps, continuously improve, and iterate on code and process in a way that helps the organization grow.

On every step in the journey to full CI/CD, the development team's productivity will rise, as well as the velocity of the entire business.

A typical development workflow

You can apply continuous integration in most software projects, including web applications, cloud-native microservices, mobile apps, system software, IoT / embedded systems and more.

For example, Semaphore integrates with GitHub, bringing CI/CD into the standard pull request-based development process.

Here's a typical continuous integration workflow that Semaphore users practice on a daily basis:

  • A developer creates a new branch of code in GitHub, makes changes in the code, and commits them.
  • When the developer pushes her work to GitHub, Semaphore builds the code and then runs the automated test suite.
  • If Semaphore detects any errors in the CI pipeline (status: red), the developer gets a Slack notification or sees a message on her personal dashboard on Semaphore.
    • If the developer has opened a pull request, Semaphore also reports the CI status on the pull request page on GitHub.
  • Otherwise, the user gets a notification that CI has passed (status green). Semaphore automatically initiates the next pipeline which deploys a new version of the application to a staging server. This allows QA or anyone else on the team to test the changes in a production-like environment.
  • Once another developer has verified the changes in a peer review, the author can merge the new branch of code into the master branch.
  • Semaphore runs one more build and test pipeline on the master branch, and when it passes it deploys a new version of the code to production. The team gets a notification about a new release via Slack.

Continuous Integration best practices

Treat master build as if you're going to make a release at any time. Which implies some team-wide don'ts:

  • Don't comment out failing tests. File an issue and fix them instead.
  • Don't check-in on a broken build and never go home on a broken build.

Keep the build fast: up to 10 minutes. Going slower is good but doesn't enable a fast-enough feedback loop.

Parallelize tests. Start by splitting by type (eg. unit and integration), then adopt tools that can parallelize each.

Have all developers commit code to master at least 10 times per day. Avoid long-running feature branches which result in large merges. Build new features iteratively and use feature flags to hide work-in-progress from end users.

Wait for tests to pass before opening a pull request. Keep in mind that a pull request is by definition a call for another developer to review your code. Be mindful of their time.

Test in a clone of the production environment. For example, you can define your CI environment with a Docker image, and make the CI environment match production 100%. An alternative is to customize the CI environment so that bugs due to difference with production almost never happen.

Use CI to maintain your code. For example, run scheduled workflows to detect newer versions of your libraries and upgrade them.

Keep track of key metrics: total CI build time (including queue time, which your CI tool should maintain at zero) and how often your master is red.

Did you find the post useful? Let me know by ❤️-ing or 🦄-ing it below!

What would you like to learn next about CI/CD? Let me know in the comments.

Thanks for reading. 🙏

Top comments (9)

gypsydave5 profile image
David Wickes

And best of all is you can deploy on Fridays...

itenev profile image
Ивелин Тенев

...and never go home for the weekend.

kanlanc profile image
Vikranth Kanumuru

I get the building part but could u explain exactly what kinds of tests are to be runned when doing CI. Thx

markoa profile image
Marko Anastasov

Does your app have some automated tests or you're just starting out?

kanlanc profile image
Vikranth Kanumuru

Just starting out

Thread Thread
markoa profile image
Marko Anastasov

I think you should always run all tests.

A large project may include some tests that run against live staging or production instances, and in that case such tests can only run after deployment.

The topic of "how to grow a test suite" probably deserves a blog post of its own. :)

Thread Thread
kanlanc profile image
Vikranth Kanumuru

Yes, it really would, I am searching for what exactly it consists of so that I cN get an idea

stevezieglerva profile image
Steve Ziegler

Thanks for the post. I thought the builds were usually from master. Are you creating the build for tests from a feature branch?

markoa profile image
Marko Anastasov

Yes, I'd always run CI on feature branches too. Why wouldn't you? :) You get feedback and safe space to fix all errors before merging. It's clear whose job it is to make the build green, and you're not blocking anyone.