CI Servers Explained: A Detailed Guide

CI servers are key tools in modern software development. They automate code integration and testing to speed up delivery and reduce errors. They ensure smooth workflows, improve teamwork, and provide quicker feedback, making them essential for continuous integration and delivery.

This article covers what CI servers are, how they work, key features, top tools, and their role in automated testing.

Understanding CI Servers

CI servers automate the integration of code changes into a shared repository, handling tasks such as building, testing, and deployment. This automation enables developers to identify issues promptly and accelerate software releases.

Key functionalities of CI Servers

Here are the core functionalities that make CI servers essential in the software development workflows:

• Automated Build: The CI server automatically compiles and assembles your application whenever code changes are pushed to the repository.
• Automated Testing: After each code update, the server runs tests to ensure the new code doesn’t break existing functionality.
• Continuous Integration: CI servers continuously merge and validate changes from multiple developers, keeping the shared codebase stable.
• Integration with Version Control: The servers connect with tools like GitHub or GitLab to automatically detect code changes and trigger builds and tests.

How CI Servers Work

CI servers automate code integration and application building, allowing developers to catch and resolve issues early during the development process.

1. Monitor Version Control Systems

CI servers constantly check version control systems like Git for new code changes. They do this by either regularly polling the repository or using webhooks to get immediate notifications when changes are made. This way, the CI server always works with the latest version of the code.

2. Trigger Builds

When the CI server finds new changes in the repository, it starts a build automatically. It gets the latest code and sets up a clean environment to ensure that the build isn’t affected by leftovers from previous builds.

3. Execute Build Steps

The CI server executes a series of predefined build steps, as specified in configuration files such as Jenkinsfile, .gitlab-ci.yml, or .travis.yml. These steps include compiling the code, running tests, and checking code quality.

Example:

pipeline {

    agent any

    stages {

        stage('Build') {

            steps {

                sh 'mvn clean install'  // Compile the code using Maven

            }

        }

        stage('Test') {

            steps {

                sh 'mvn test'  // Run unit tests

            }

        }

    }

}

4. Run Tests and Quality Checks

After a successful build, the CI server automatically runs tests to find bugs and errors. These tests, such as unit tests and integration tests, ensure the application works as expected and meets code quality standards.

5. Report Results

After completing the build and tests, the CI server generates a report with the results and notifies the development team. This notification can be sent via email, chat applications, or by updating the status directly in the version control system to indicate whether the changes passed or failed the tests.

6. Store Build Artifacts

If the build and tests succeed, the CI server saves the resulting files (like compiled code or Docker images) in a special storage system. This storage, called an artifact repository, allows the team to easily find and use these files later when they’re ready to deploy the software.

stage('Deploy to Docker') {

    steps {

        sh 'docker build -t myapp:latest .'  // Build Docker image

        sh 'docker push myapp:latest'  // Push Docker image to registry

    }

}

This code shows how to deploy an Artifact to the Docker Registry.

7. Trigger Deployments

Sometimes, CI servers automatically deploy the application to staging or production environments. They may run quick tests, like smoke tests, to confirm everything works and can roll back changes automatically if something goes wrong.

8. Maintain Build History

CI servers keep a record of all build results, helping teams track patterns and recurring problems. This history allows developers to identify and fix performance issues, making future builds and deployments more efficient.

Popular CI Servers and Tools

Here are some widely used CI servers and tools that help teams automate builds, tests, and deployments effectively:

• Jenkins: Jenkins is a customizable open-source CI tool with a vast plugin library for easy integration and automation. Though setup can be complex, strong community support keeps it a go-to choice for many teams.

• Travis CI: It is a cloud-based tool that helps developers test and build their code automatically. It is easy to set up and works well with GitHub, making it popular for open-source projects.
• CircleCI: Designed for the cloud, this CI tool simplifies testing and deployment with fast performance and easy integration with GitHub and Bitbucket. It offers flexible plans, including a free tier, but advanced features may require a paid plan.

• GitLab CI/CD: This one is a built-in tool in GitLab that automates testing and deployment. It is easy to use, especially for GitLab users, and does not require extra setup. It supports both cloud and self-hosted options, giving teams flexibility.
• TeamCity: A tool by JetBrains, TeamCity helps automate testing and deployment. It is easy to set up and has a user-friendly interface. It offers powerful features, but the free version has limitations, and the paid plans can be costly.
• Bamboo: A CI/CD tool by Atlassian that integrates well with Jira and Bitbucket. It is easy to use and supports both cloud and self-hosted setups. It offers powerful features, but it is not free and can be expensive for small teams.

• GitHub Actions: It is also a CI/CD tool built into GitHub that automates testing and deployment. It is easy to use, especially for GitHub projects, and offers many pre-built workflows.
• Azure DevOps: This CI/CD tool by Microsoft helps automate testing and deployment. It integrates well with Azure and other Microsoft services, making it great for Windows-based projects.

• Bitbucket Pipelines: This cloud-based CI/CD tool is built into Bitbucket. It is easy to set up and works seamlessly with Bitbucket repositories. It has a simple, YAML-based configuration but offers limited free build minutes.
• GoCD: It is an open-source CI/CD tool focused on advanced workflow automation. It supports complex pipelines and allows better visualization of deployment stages. It is free to use, but setup and management can be challenging for beginners.

Choosing the right CI/CD tool depends on the project’s size, complexity, and team expertise. For simpler projects, tools like CircleCI or GitHub Actions are quick to set up, while larger, more complex projects may require the flexibility of Jenkins or GitLab CI/CD.

Consider factors like team skill level, infrastructure needs, and budget to choose the most suitable solution.

Talk to an Expert

CI Servers and Automated Testing

CI servers automate code integration, testing, and deployment by tracking changes in repositories, triggering builds, and running tests. This helps catch issues early, ensures code quality, and provides quick feedback. By reducing manual effort and keeping builds consistent, CI servers make development faster and more reliable.

BrowserStack boosts test automation in CI/CD by providing access to a real device cloud with 3500+ real devices and browsers, ensuring thorough cross-platform testing. BrowserStack enhances test automation in CI/CD pipelines by:

• Real User Environment: Running tests on 3,500+ real browsers and devices to catch environment-specific bugs missed by emulators
• Parallel Testing: Running multiple tests simultaneously to speed up execution and accelerate releases
• Self-Healing Tests: Using AI to adapt to minor UI changes, reducing test flakiness, and increasing reliability
• Scalability: Offering a cloud-based infrastructure that scales on demand, reducing the need for internal test environments
• CI/CD Integration: Seamlessly integrating with tools like Jenkins, GitLab CI/CD, CircleCI, Travis CI, and GitHub Actions

These features make BrowserStack a powerful choice for teams aiming to streamline test automation and deliver high-quality software faster.

Conclusion

CI servers automate integration, testing, and deployment, enabling faster, more reliable software releases. Integrating tools like BrowserStack enhances test accuracy, speeds up testing, and ensures software quality across various devices and browsers.