Continuous Integration

Continuous Integration (CI) is a software development practice where developers frequently integrate their work with the project's Integration branch and create a build.

Integration is the act of submitting your private work (modified code) to the common work area (the potential software solution). This is technically done by merging your private work (personal branch) with the common work area (Integration branch). Or we can say, pushing your private branch to the remote branch.

CI is necessary to bring out issues encountered during the integration as early as possible. This can be understood from the following diagram, which depicts various issues encountered during a single CI cycle.

A build failure can occur due to either an improper code or a human error while doing a build (assuming that the tasks are done manually). An integration issue can occur if the developers do not rebase their local copy of code frequently with the code on the Integration branch. A testing issue can occur if the code does not pass any of the unit or integration test cases.

In the event of an issue, the developer has to modify the code to fix it:

CI process

Agile runs on CI

The Agile software development process focuses mainly on fast delivery, and CI helps Agile in achieving that speed. But how does CI do that? Let us understand by using a simple case.

Developing a feature involves many code changes, and between every code change, there are a set of tasks to perform, such as checking-in the code, polling the version control system for changes, building the code, unit testing, integration, building on the integrated code, integration testing, and packaging. In a CI environment, all these steps are made fast and error-free by using a CI tool such as Jenkins. 

Adding notifications makes things even faster. The sooner the team members are aware of a build, integration, or deployment failure, the quicker they can act. The following diagram depicts all the steps involved in a CI process:

CI process with notifications

In this way, the team quickly moves from feature to feature. In simple terms, the agility of the agile software development is greatly due to CI.

Types of projects that benefit from CI

The amount of code written for the embedded systems presents inside a car is more than the one present inside a fighter jet. In today's world, embedded software is inside every product, modern or traditional. Be it cars, TVs, refrigerators, wrist watches, or bikes; all have little or more software-dependent features. Consumer products are becoming smarter day by day. Nowadays, we can see a product being marketed more using its smart and intelligent features than its hardware capabilities. For example, an air conditioner is marketed by its wireless control features, and TVs are being marketed by their smart features, like embedded web browsers, and so on.

The need to market new products has increased the complexity of products. This increase in software complexity had brought the Agile software development and CI methodologies to the limelight, though there were times when agile software development was used by a team of no more than 30-40 people that were working on a simple project. Almost all types of projects benefit from CI: mostly the web-based projects, for example, the e-commerce websites, and mobile phone apps.

CI and agile methodologies are used in projects that are based on Java, .NET, Ruby on Rails, and every other programming language present today. The only place where you will see it not being used is in the legacy systems. However, even they are going agile. Projects based on SAS, Mainframes; all are trying to benefit from CI.