What is Continuous Integration and what are the benefits?

Developing software in today's world is a complex process involving numerous participants such as developers, testers, or teams for larger or long-term projects. Each of them takes on subtasks - from individual functions to the user interface (GUI) to checking functionality and security. To detect potential issues in merging and compatibility of different program parts and instances early on, more elaborate projects now mostly use a process known as "Continuous Integration" (CI). It aims to accelerate development to a minimum, test existing components, and enable a secure distribution (Continuous Delivery and Deployment) of programs and updates.

Contents:
What is the principle behind "Continuous Integration"?
What methods does continuous integration use?
How does continuous integration work?
What benefits does continuous integration offer?
Does continuous integration require a special environment?

What is the principle behind "Continuous Integration"?

Until the second decade of the new millennium, software development mostly followed a purely procedural and linear course, where multiple teams or developers solved tasks independently. Subsequently, the individual components were manually assembled and underwent a testing or alpha phase, where most errors were identified and rectified. Once a product was deemed marketable, it was directly delivered to users via floppy disk, CD, DVD, and more recently media like Blu-Ray, with a single functional and reliable version being the primary focus. This practice is now considered outdated - a consistently stable, functional, and secure software requires long-term development, allowing vulnerabilities to be identified and addressed post-development.

This translates into increased effort and demand for the integration of individual program parts - these must be constantly checked for compatibility and correct functioning with each other. Continuous integration provides a solution to this problem by assembling the components not only at the end of the development process, but instead at short intervals - usually daily, weekly, or after each development stage. The reason behind this is that significant problems often arise when the individual components are integrated late, as they are not or insufficiently coordinated. These problems are often so extensive that many developers refer to this step as the "integration hell".

Continuous integration aims to identify and eliminate these difficulties early on and already during development. It not only shortens the time until a finished product is ready, but also helps to improve quality. Furthermore, continuous integration increases efficiency by enabling the involved programmers to better coordinate with each other and avoid task duplication and extra effort in testing and integration. Due to its advantages, it has largely become a standard for complex projects such as Content Management Systems (CMS).

What methods does continuous integration use?

In order for continuous integration to run successfully, some basic rules, requirements, and conditions must be met. Particularly important are:

• Central, collective source code with a branched version control system like Git or Subversion (SVN)
• Short intervals between test cycles to ensure frequent and rapid continuous integration
• Automation of important steps such as compiling, linking, and testing
• Frequent and regular integration to quickly implement changes, archive progress, and facilitate debugging
• Development of specialized tests for as many changes as possible, which can later be automated
• Collective use of a single branch in the version control system
• Automatic testing of code and insertion into the used repositories (Continuous Delivery)
• Automatic release and transition after the testing phase from the experimental to the productive stage (Continuous Deployment)

Together, this approach is known as CI/CD, where CD stands for Continuous Delivery and Continuous Deployment. It consists of three phases that lead to high-quality software at high speed and with minimal time and effort. All three stages are interconnected and can run concurrently, avoiding any downtime where one team has to wait for another's results, for example.

How does continuous integration work?

A fundamental characteristic of continuous integration is the automation of many processes such as testing and merging different development branches. Custom scripts continuously build a runnable version from existing repositories at short intervals, progressing through alpha or beta phases. These versions are known as Nightly Builds, as they are typically generated daily during the night - outside working hours and after changes have been submitted - and immediately made available to all involved parties. Various tools such as the web application GitLab or the software system Jenkins are used for this purpose.

It is common practice, especially in the open-source community, for programmers and development teams to freely share the created Nightly Builds with all interested parties. This ensures users always have an up-to-date software version and contribute to identifying bugs and vulnerabilities early, before they reach a stable release. It is a special form of beta testing that anyone can voluntarily participate in. It is important to note that a Nightly Build is always in an experimental stage. Therefore, they should never be used on production or mission-critical systems as their current development status, performance, security, and stability cannot be guaranteed.

What are the benefits of continuous integration?

Although continuous integration is a relatively new process that only began to be used in its early stages around 2010, it has become established in software development since around 2015. This is mainly due to the various significant advantages it offers compared to the previously common practices. It helps introduce or improve the following aspects:

• Short deadlines between writing and checking in the code (check-in) into a version control system
• Continuous testing enables early detection of errors in the code or integration
• Many small changes instead of fewer large ones facilitate debugging and error tracing
• Automated and continuous code quality and functionality checks
• An up-to-date version available permanently for testing, demonstrations, or distribution
• Increased efficiency with lower workload and better quality
• Possible combination with Continuous Delivery and Continuous Deployment

To fully benefit from these advantages, it is recommended to use appropriate environments that include different tools for continuous integration.

Does continuous integration require a special environment?

While continuous integration can theoretically be carried out independently of the developers' tools on a central instance, this entails a significant effort in setup, customization, and maintenance. Therefore, in most cases, it is more sensible to use a platform such as GitLab, which provides the necessary services. Many companies now also offer CI/CD as part of Software as a Service (SaaS) or Infrastructure as a Service (IaaS). These services include not only version control but also various other tools such as a centralised development environment that all participants can access to standardise procedures and workflows. Often, specially paid offers also include additional useful tools such as the project management software Redmine. Many of the tools offered, including GitLab and Redmine, operate under an open-source license, making it possible to set up a suitable network and working environment for continuous integration on your own Virtual Private Server or Dedicated Server with minimal financial outlay.

Photo: Gerd Altmann on Pixabay