CI Server: How It Works and Should You Run Your Own?

What Is a CI Server (Build Server)?

A CI server, also known as a build server, is a tool used in Continuous Integration (CI) processes to automatically build, test, and validate code changes in a software development project.

It is designed to monitor a version control system, trigger builds upon detecting new commits, and provide feedback on the success or failure of those builds. This helps developers identify and fix issues early in the development cycle, leading to faster and more stable software releases.

Why Are CI Servers Important?

CI servers are important for several reasons:

  • Improved collaboration: A CI server allows developers to work on the same codebase simultaneously without stepping on each other’s toes. It merges changes from multiple sources and ensures that the integrated code is functional and stable.
  • Early detection of issues: By automatically building and testing code changes, a CI server helps identify integration issues, bugs, and broken dependencies early in the development cycle. This allows developers to fix problems before they escalate, reducing the time and effort needed for debugging.
  • Faster feedback: A CI server provides rapid feedback on the status of the codebase, enabling developers to address issues quickly and efficiently. This short feedback loop helps maintain a high level of code quality and prevents the accumulation of technical debt.
  • Automated testing: CI servers run a suite of automated tests against the codebase, ensuring that every change passes the necessary quality checks. This reduces human error and increases the reliability and stability of the software.
  • Consistent build environment: A CI server maintains a consistent build environment, ensuring that every build is conducted using the same tools, dependencies, and configurations. This eliminates the “it works on my machine” problem and promotes consistency across the development team.
  • Streamlined deployment: By automating the build, test, and deployment processes, CI servers help streamline the software release process. This enables organizations to release updates and new features more frequently, improving their ability to respond to market demands and customer feedback.

How CI Servers Work

Continuous Integration (CI) servers automate the process of integrating code changes from multiple developers and building the application to catch issues early in the development process. Here’s a high-level overview of how CI servers work:

  1. Monitor version control systems: CI servers monitor the version control system (e.g., Git, Subversion, or Mercurial) for new commits or changes. They can either poll the repository periodically or use webhooks to receive notifications about new commits.
  2. Trigger builds: When new changes are detected, the CI server automatically triggers a build process. This involves fetching the latest code from the version control system and creating a clean environment to run the build.
  3. Execute build steps: The CI server follows a predefined build script or configuration file (e.g., Jenkinsfile, .gitlab-ci.yml, or .travis.yml) that specifies the steps to be executed during the build process. These steps may include:
    1. Compiling the source code
    2. Running unit tests and integration tests
    3. Static code analysis and code quality checks
    4. Packaging the application for deployment (e.g., creating a JAR file or Docker image)
  4. Report results: After the build process is complete, the CI server reports the results to the development team. This can include sending notifications via email, Slack, or other communication channels, displaying build status on dashboards, or updating pull request statuses in the version control system.
  5. Store build artifacts: If the build is successful, the CI server may store the resulting artifacts (e.g., packaged applications or Docker images) in a repository or artifact storage system (e.g., Nexus, Artifactory, or Docker Registry) for later deployment.
  6. Trigger deployments: In some cases, the CI server may also initiate deployments to various environments (e.g., staging, production) as part of a Continuous Deployment (CD) process. This typically involves additional steps, such as deploying the application to a target environment, running smoke tests, and rolling back in case of failures.
  7. Maintain build history: CI servers maintain a history of build results, allowing teams to review past builds, identify trends, and track the progress of their projects.

By automating these tasks, CI servers help development teams maintain high-quality code, catch issues early, and streamline the software development lifecycle. The specific implementation details and features may vary depending on the CI server tool used. However, the general process of monitoring version control systems, triggering builds, executing build steps, and reporting results remains consistent across most CI server tools.

Should You Run Your Own CI Server?

In the past, most development teams would run open source or commercial CI servers on their local infrastructure. However, in recent years, it is becoming more common to use CI as a cloud service, transferring the responsibility of installing and configuring CI servers to a service provider. Here are some of the pros and cons to weigh before deciding whether to invest in your own CI infrastructure or rent it as a service.


  • Customization: Running your own CI server allows for complete customization to suit your specific project requirements, workflows, and infrastructure. You can tailor the CI server to work seamlessly with your tools and processes.
  • Control: Running your custom CI server provides greater control over the underlying infrastructure, which can be beneficial in terms of performance, security, and compliance.
  • Cost: Depending on your team size and project requirements, building and maintaining your CI server might be more cost-effective than using a commercial or cloud-based CI service, especially if you have access to spare infrastructure resources. Cloud-based CI services are typically priced on a pay per use or subscription basis.


  • Development and maintenance overhead: Running your own CI server requires significant efforts and ongoing maintenance to keep up with new technologies, security updates, and bug fixes. This can divert resources from your core product development.
  • Scalability: Commercial and cloud-based CI services often provide built-in scalability, automatically adjusting resources to meet demand. With your own CI server, you’ll need to handle scaling and resource management, which can be challenging and time-consuming.
  • Integration: Cloud-based CI tools typically offer built-in integration with popular version control systems, issue trackers, and deployment platforms. When running your own CI server, the server platform will probably provide built-in integrations for most popular systems, but it can be more complex to connect and troubleshoot these integrations.
  • Learning curve: A local CI server may have a steeper learning curve for new team members, as cloud-based systems are typically easier to use.

Continuous Integration with Codefresh

Codefresh is a modern software delivery platform that includes Continuous Integration/Deployment and GitOps modules. Continuous integration works by creating pipelines where each step is a docker container. This allows for maximum flexibility as one can connect different programming languages and tools in the same pipeline combining even different versions of the same tool.

At the same time, the CI components include several enterprise features such as manual approvals, image annotations, multiple trigger types and even a unique pipeline debugger that allows you to pause a pipeline and inspect its current status with the full trigger context.
Even though Codefresh CI works with all platforms and deployment targets, it is especially powerful with containers and Kubernetes clusters as it allows for one-click integration with different Docker registries and Cloud providers in an agnostic manner.

The World’s Most Modern CI/CD Platform

A next generation CI/CD platform designed for cloud-native applications, offering dynamic builds, progressive delivery, and much more.

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