Continuous Integration (CI) is a software development practice that encourages developers to integrate their code into a shared repository frequently, preferably several times a day. Each integration is then verified by an automated build and automated tests. While automated testing is not strictly part of CI it is typically implied.
One of the key benefits of integrating regularly is that you can detect errors quickly and locate them more easily. As each change introduced is typically small, pinpointing the specific change that introduced a defect can be done quickly.
Understanding Continuous Integration
The concept of Continuous Integration (CI) is central to modern software development practices. CI is a coding philosophy and set of practices that drive development teams to implement small changes and check in code to version control repositories frequently. Because most modern applications require developing code in different platforms and tools, the team needs a mechanism to integrate and validate its changes.
The goal of CI is to provide rapid feedback so that if a defect is introduced into the code base, it can be identified and corrected as soon as possible. CI was first introduced as a part of Extreme Programming (XP), a software development methodology that encourages frequent "releases" in short development cycles, which is intended to improve productivity and introduce checkpoints at which new customer requirements can be adopted.
Benefits of Continuous Integration
Continuous Integration is cheap. Not integrating continuously is expensive. If you don’t follow a continuous approach, you’ll have longer periods between integrations. This makes it exponentially more difficult to find and fix problems. Such integration problems can easily knock a project off-schedule, or cause it to fail altogether.
CI, when done well, removes uncertainties and reduces times to release software. It paves the way to other important practices such as Continuous Delivery and Continuous Deployment. Also, it helps keep your application deployable throughout its lifecycle and ensures that you get extensive test coverage.
Principles of Continuous Integration
Continuous Integration is backed by several important principles and practices. The practices of CI are designed to address the difficulties that arise when an application is in the process of being developed.
CI involves making small changes to software, and then building and testing that software. Often, you integrate and test the entire application. With CI, you make small, incremental changes. Automated build-and-test steps validate these changes. This approach reduces risk and allows teams to deliver quality software more rapidly.
Implementing Continuous Integration
Continuous Integration is not just a tool you can buy and put in place - it's more of a philosophy and a set of practices. It's not something you can "do" or you're "done with". Rather, it's a constant approach to the code that you and your team are working on. The biggest part of implementing CI is a mindset shift.
Implementing CI can be broken down into a few key steps: maintain a code repository, automate the build, make the build self-testing, everyone commits to the mainline every day, every commit (to mainline) should be built, keep the build fast, test in a clone of the production environment, make it easy to get the latest deliverables, everyone can see the results of the latest build, and automate deployment.
Tools for Continuous Integration
There are many Continuous Integration tools available that can help you accomplish these tasks, from open source to commercial. Some of the more popular ones include Jenkins, Travis CI, CircleCI, and TeamCity. These tools provide a robust platform for handling all the tasks associated with Continuous Integration.
These tools integrate with your existing toolchain - version control systems like Git, and build tools like Maven or Gradle. They provide a way to script the steps that need to be taken after every check-in or on a regular basis to perform a build. They also provide a way to trigger these scripts automatically, or on a schedule, and then capture the output of the build including any test results.
Challenges in Implementing Continuous Integration
While CI is beneficial, it's not without its challenges. These include: convincing everyone to integrate frequently, creating a comprehensive and fast test suite, maintaining a clone of the production environment, and making the build self-testing.
Overcoming these challenges often involves a combination of good design, good practices, and a supportive culture. From a technical point of view, a key practice is to design for testability. From an organizational point of view, a key practice is to create a culture that values and understands the importance of good testing and frequent integration.
Continuous Integration and High-performing Engineering Teams
Continuous Integration is a key element of high-performing engineering teams. It allows teams to move faster while still ensuring the quality of the software they are delivering. It also promotes more productive and positive teams by reducing the risks associated with integration, allowing for more time to be spent on developing new features.
High-performing engineering teams typically use CI along with other practices such as Test-Driven Development (TDD), Pair Programming, and Infrastructure as Code. These practices are often used in conjunction with one another to achieve the best results.
Continuous Integration and Agile Development
Continuous Integration is a practice used in Agile development methodologies such as Scrum or Kanban. The idea is that developers will frequently integrate their code with a shared mainline, which leads to multiple integrations per day. Each integration is verified by an automated build and automated tests to detect integration errors as quickly as possible.
This practice, along with Test-Driven Development (TDD) and Pair Programming, helps increase the speed and efficiency of software development teams, allowing them to deliver more value in less time.
Continuous Integration and DevOps
Continuous Integration is a fundamental practice in DevOps. DevOps is a set of practices that automates the processes between software development and IT teams, in order that they can build, test, and release software faster and more reliably. The concept of CI/CD pipeline is central to DevOps.
A CI/CD pipeline helps automate steps in the software delivery process, such as initiating code builds, running automated tests, and deploying to a staging or production environment. Automated pipelines remove manual errors, provide standardized feedback loops to developers, and enable fast product iterations.
Continuous Integration is a key practice for any software development team aiming to deliver high-quality software, fast. It's not a one-size-fits-all solution, but with the right practices, tools, and culture, it can significantly improve the productivity and happiness of a software development team.
While it can be challenging to implement, the benefits of CI, such as reduced risk and faster feedback cycles, make it an essential practice for any high-performing engineering team. By integrating regularly, you can ensure that your software is always in a state that can be released, allowing you to deliver new features to your users more quickly.