[box] CI/CD is a method to frequently deliver apps to customers by introducing automation into the stages of app development. The main concepts attributed to CI/CD are continuous integration, continuous delivery, and continuous deployment. CI/CD is a solution to the problems integrating new code can cause for development and operations teams.
Specifically, CI/CD introduces ongoing automation and continuous monitoring throughout the lifecycle of apps, from integration and testing phases to delivery and deployment. Taken together, these connected practices are often referred to as a “CI/CD pipeline” and are supported by development and operations teams working together in an agile way with either a DevOps or Site reliability engineering (SRE) approach[/box] .
Continuous integration (CI) and continuous delivery (CD) embody a culture, set of operating principles, and collection of practices that enable application development teams to deliver code changes more frequently and reliably. The implementation is also known as the CI/CD pipeline.
Continuous integration 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 technical goal of CI is to establish a consistent and automated way to build, package, and test applications. With consistency in the integration process in place, teams are more likely to commit code changes more frequently, which leads to better collaboration and software quality.
Continuous delivery picks up where continuous integration ends. CD automates the delivery of applications to selected infrastructure environments. Most teams work with multiple environments other than the production, such as development and testing environments, and CD ensures there is an automated way to push code changes to them.
Continuous deployment (the other possible “CD”) can refer to automatically releasing a developer’s changes from the repository to production, where it is usable by customers. It addresses the problem of overloading operations teams with manual processes that slow down app delivery. It builds on the benefits of continuous delivery by automating the next stage in the pipeline.
In modern application development, the goal is to have multiple developers working simultaneously on different features of the same app. However, if an organization is set up to merge all branching source code together on one day (known as “merge day”), the resulting work can be tedious, manual, and time-intensive. That’s because when a developer working in isolation makes a change to an application, there’s a chance it will conflict with different changes being simultaneously made by other developers. This problem can be further compounded if each developer has customized their own local integrated development environment (IDE), rather than the team agreeing on one cloud-based IDE.
Continuous Integration (CI) is a phase in the software development cycle where code from different team members or different features are integrated together. This usually involves merging code (integration), building the application and carrying out basic tests all within an ephemeral environment.
In the past, the code was integrated at an “integration phase” of the software development life cycle. This phase came after different teams would have spent weeks, months or even years working in separately, dedicated to different (parts of) application or services. You can guess how painful the integration phase of the project would have been. It was not uncommon to spend weeks or even months in this phase. This was during the waterfall era.
With Extreme Programming (XP) and agile, integration became frequent with developers integrating as often as possible usually soon after a unit is complete. This is done on the shared source code repository. The frequent integration became automated and continuous which prompted the need for some kind of checks before the new code is integrated. Thus, Continuous Integration.
CI workflows vary a lot depending on tools, programming language, project and many other factors but a common flow has these steps.
• Pushing to the code repository : Typically, there would have a code repository and some kind of workflow for contributing new code. Depending on the workflow, committing code kicks off the CI pipeline, which often starts with static code analysis.
• Static analysis : Static (code) analysis is done on the code base of the application without the need to run the software. The goal here is to ensure the code doesn’t have possible bugs and conforms to standard formatting and styling.
• Pre-deployment testing
• Packaging and deployment to the test environment
• Post-deployment testing
Depending on the kind of project, the application is built, packaged, sent to a test or staging environment (that mimics production). This ensures that the integrated changes build well with other parts and can be deployed for a functional test can to be carried out. It’s at this phase that we also verify that the new changes are compatible with other libraries and the deployment environment. This is phase should also automated.
For tests that need the application to be deployed, this phase of the CI pipeline is where they’re run. The tests vary depending on tools, frameworks, and language of the application but they’re usually functional integration and performance tests. Successful execution of this phase ends the CI pipeline for the changeset signalling it’s good enough for users.
Once the CI pipeline completes successfully, the deployed application could undergo a manual test by a “user” or the QA team to ensure that it fits the client’s requirements. The packages or artifacts generated by the CI pipeline can now be taken/deployed to production. This can also be automated with a successful implementation of a Continuous Delivery (CD) pipeline.
Following the automation of builds and unit and integration testing in CI, continuous delivery automates the release of that validated code to a repository. So, in order to have an effective continuous delivery process, it’s important that CI is already built into your development pipeline. The goal of continuous delivery is to have a codebase that is always ready for deployment to a production environment.
In continuous delivery, every stage—from the merger of code changes to the delivery of production-ready builds—involves test automation and code release automation. At the end of that process, the operations team is able to deploy an app to production quickly and easily.
The final stage of a mature CI/CD pipeline is continuous deployment. As an extension of continuous delivery, which automates the release of a production-ready build to a code repository, continuous deployment automates releasing an app to production. Because there is no manual gate at the stage of the pipeline before production, continuous deployment relies heavily on well-designed test automation.
In practice, continuous deployment means that a developer’s change to a cloud application could go live within minutes of writing it (assuming it passes automated testing). This makes it much easier to continuously receive and incorporate user feedback. Taken together, all of these connected CI/CD practices make deployment of an application less risky, whereby it’s easier to release changes to apps in small pieces, rather than all at once. There’s also a lot of upfront investment, though, since automated tests will need to be written to accommodate a variety of testing and release stages in the CI/CD pipeline.
CI/CD tools can help a team automate their development, deployment, and testing. Some tools specifically handle the integration (CI) side, some manage development and deployment (CD), while others specialize in continuous testing or related functions.
One of the best known open source tools for CI/CD is the automation server Jenkins. Jenkins is designed to handle anything from a simple CI server to a complete CD hub.