Continuous integration and continuous deployment
Before you change or deploy your company's infrastructure, understand what you plan to build by exploring the concepts behind continuous integration (CI) and continuous delivery or deployment (CD). In this unit, you learn about CI/CD pipelines and how to apply CI and CD with GitHub Actions.
CI and CD are operating practices that introduce continuous automation and monitoring into all the phases of software development, testing, and deployment. Developer teams use CI and CD to be more productive and help reduce problems that can arise when integrating new code into an existing code base.
Continuous integration
Before the development of CI/CD tools, the entire develop-test-deploy-test process was manual. Automated test suites were available, but they had to be run manually or at scheduled times by expert teams.
One of the most significant challenges software developers faced was merge day. Merge day happened because most software development teams worked on the same code in different source control branches with minimal tests. On merge day, all code changes were integrated back into the main branch. As a result, an entire day had to be dedicated to solving integration issues as the team members' branches merged and intersected in the main branch.
A critical CI principle is to merge all new changes back into the main branch as often as possible. Continually merging changes helps avoid the merge day "integration hell" that occurred when many developers combined their changes at once.
CI requires that teams frequently implement and integrate the smallest changes in the code. Implementing CI means that teams can constantly test, compile, deploy, and then test again in production. The goal of CI is to detect and avoid production problems caused by code changes before they can affect the main code branch or deploy to customers.
Continuous delivery and deployment
Continuous delivery picks up where CI ends, and automates the delivery process to the selected infrastructure environment. You can use continuous delivery to release changes quickly and sustainably. After you use continuous delivery, you decide in advance whether to deploy the changes daily, weekly, monthly, or on another schedule that suits your business requirements.
Continuous deployment goes one step farther by automatically releasing changes that pass all stages of the CI/CD pipeline to production. Continuous deployment is one of the most advanced processes in software development, and requires code that tests all aspects of the application's functionality without human intervention.
CI/CD pipelines
A pipeline comprises the collective processes that run when a specified event occurs. A large number of events are part of software development, and a CI/CD pipeline must support all related events. When an event triggers the pipeline, all the listeners for this event are triggered and the first stage of the process starts.
A CI/CD pipeline runs when a new code change triggers it. In most cases, the process begins by cloning or downloading source code. Then the next step triggers, and so on.
Every time a code change triggers a CI/CD run, all steps in the pipeline execute. If there's an error in a step, the pipeline stops. Workflows can contain logic jumps so that some stages don't execute under certain conditions, but the overall pipeline continues to execute.
GitHub Actions
GitHub Actions supports all GitHub related events and automates the CI/CD pipeline in this module. In GitHub Actions, each step defines actions either in JavaScript or by using a Docker container. Actions are easy to create, and form the building blocks of the pipeline steps.
You can use GitHub Actions to seamlessly integrate all your GitHub hosted code with an automation workflow. The workflow handles multiple tasks to integrate the code across several environments.
GitHub Actions is a popular provider for CI/CD pipelines because of its open-source model. Because workflows are open-source, they're stored in repositories available to anyone on the platform. GitHub users may use each other's actions or create their own custom actions without installing or configuring anything else.
The ability to share actions among users means that you don't need to rewrite repeated code or stages, but can use or customize existing actions. In the next units, you use GitHub Actions in a Docker container to define a CI/CD pipeline that implements continuous deployment of an application.