What is Continuous Integration?

Continuous integration is the practice of continuously integrating code changes from different developers working on the same code into a single software project. This integration usually updates automatically as an ongoing process throughout the day to ensure that all changes to the code are properly recorded. This strategy is an essential part of an Agile software development system, which is built around the concept of collaboration, designing for scale, and building sustainability.

Continuous Integration Diagram

In 1994, the term “continuous integration” was first introduced by American software engineer Grady Booch, who is best known developing the Unified Modeling Language (UML) but also for his innovative work in software architecture and collaborative developer environments. Continuous integration has been regularly employed since 1997 and is now widely accepted as best practice for software development. Although the process of continuous integration may look a bit different today than it did 20 years ago, the theory behind it nonetheless remains the same.

One way to understand how important continuous integration is would be to think of coding software like building a house. In this case, you have many different builders, or developers, all constructing their specific parts of the building, or software, offsite. They might start and stop their work at different times, and an error or deviation in any one part of the architecture could be enough to make the rest of the house, or program, unstable or even completely unusable.

In this metaphor, when you add in continuous integration, builders are required to visit the site multiple times a day to install the piece of work they have completed to ensure that all the parts are working together properly. Whether it is a window frame or roof, it needs to be done correctly and tested to ensure that it’s right for the existing parts of the house. In that same line of logic, there’s no point installing the kitchen cabinetry if the roof isn’t on yet. Continuous integration helps to minimize any potential errors or issues along the way that could come about if developers aren’t on the same page.

Why is Continuous Integration Used?

Software development is often handled by several large teams, which means it’s not unusual for it to be spread across different time zones and geographic areas. Because of this, chunks of development will happen at once, with multiple people working on the same part of software at the same time, unable to see what others are doing.

Continuous integration helps to ensure:

Time savings: This is perhaps the most significant gain, as it removes any double-up on tasks, automating all possible testing and merging processes, as well as allowing for a faster turnaround time with testing and fixes, and means less time wasted looking for bugs and errors. For project managers looking at a burn-down chart, it is easy to see tasks being completed and uploaded. Saving time also comes with the added bonus of saving a significant amount of cost.

A far more robust finished product: Regular, thorough testing of the software, much of which is automated, means less bug fixes will be needed in the next round of development. This also means there will be fewer bugs and errors in the final product, resulting in happier end users.

Increased communication: Constant code sharing increases the speed and efficiency of communication within the workplace.

Faster software releases: If a problem is found or a new virus emerges in existing software that customers are using, the development cycle to resolve these becomes much faster. A small change can be fixed, tested, and rolled out in very tight timeframes.

Overall, it makes the code more dependable, less prone to errors and bugs, saves a lot of time and money, and results in happier end users. It is a form of risk mitigation that every business should practice.

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How Does Continuous Integration Fit with Continuous Deployment?

The practice of continuous deployment ensures that the software is bug-free and ready to deploy at any point and is “continuously” deployed to maintain dependability. For example, you often get software updates on your mobile phone. This new deployment ensures that your applications are all up to date and secure. This way your software is ready to be deployed at any time and often is in order to incorporate important updates. Continuous integration is a vital part of continuous deployment because the software is constantly being updated, tested, and deemed fit for use. Since continuous deployment is the theory that at any point, the software could be deployed, or a customer might require it, it is imperative that the software be ready for use.

Eight Steps of Continuous Integration and Continuous Deployment

Simply put, the cycle of CI/CD (Continuous integration/Continuous delivery) is an eight-step, continuously-looping agile process that ensures fast, effective, and stable software development. Steps one through four fall under the umbrella of continuous integration, while steps five through eight are seen as part of the continuous delivery process.

  1. Plan: Changes to the application are planned by the product team. This could include bug fixes, performance enhancements, or new features to be added to the application.
  2. Code: The developers code the software on their local machines. Each developer has their own specific part of the system to develop or bug to resolve.
  3. Build: Once the developers have completed the second step, the new code is submitted to the code depository and the application is compiled.
  4. Test: Testers check the functionality and usability of the code. Does it do what it was designed to do? They also test whether it works with the rest of the existing code. Automated testing should be used to ensure that the new code doesn’t interfere with something else that’s already part of the package. If the code is deemed acceptable, it is merged. If there are errors that still need to be resolved, it is sent back to the developer.
  5. Release: Once it has been completed, the refined code is merged with the software and can be set to an automated release, pending approval.
  6. Deploy: The code is automatically deployed to production.
  7. Operate: At this point, the new code can now be operated within the production environment.
  8. Monitor: Application performance is continually monitored to find bugs and identify areas where performance can be enhanced. This is a continuous feedback cycle where the data collected and analyzed in this step should be fed back to the product team responsible for step one so they can continually plan changes and enhancements to the application.

Benefits of Continuous Integration

The reason so many Agile teams use continuous integration is because it works incredibly well to resolve many software development problems. It ensures that no two developers are working on the same piece of code at the same time, avoiding unnecessary doubling-up.

Continuous integration also ensures that the team is always working on the most recent software update and therefore building on the most recent changes. It means no last minute chaos on release date as everyone uploads their code and tries to check their versions against other tasks and sections of work.

With development, one line change, or even something as small as a full stop or wrong bracket can inadvertently break other parts of the software. Frequent updates make it easier to identify what caused the problem and fix it before moving on to other areas. It also forces developers to frequently save their work, and ensures that finished pieces of code are stored in a shared repository, often in the cloud, where it’s safe from localized power or internet disruptions.

Continuous integration helps avoid integration conflicts and failures. As other developers update their work, it affects other work that has not yet been submitted. Regular updates minimize these potential conflicts. In fact, any changes, conflicts or problems can be quickly identified soon after the code is submitted. This means the developer can return to their work straight away to fix it, while it is still fresh in their mind.

Constant code check-ins also help developers to create modular code that is less complex, and the automated nature of continuous integration means a reduction of time-consuming manual testing. Finally, there’s the benefit of having the constant availability of the current finished build for continuous deployment.

Challenges of Continuous Integration

There are, however, a number of challenges involved in implementing continuous integration. As with many technologies, it is an ongoing, constantly evolving field, with issues of resource allocation, lack of education, and the often involved process of automating legacy code, among other things.

Problem: The rollout of continuous integration as a new practice. When a company has been doing development already for some time and has never used continuous integration, trying to implement the practice all at once can quickly become overwhelming or seem impossible. Implementing continuous integration needs to be a journey, gradually moving from a manual system to a highly automated development environment. Finding the right code repository, training the developers to update, getting the testers working alongside the developers, it all takes time, patience, and a lot of collaboration across teams. There are also many decisions to be hashed out along the way, such as: should UX or functional testing happen first? Should testing be automated? Which software is best? It is a big change in the day-to-day operations of a business as well as the culture of accountability.

Solution: A staggered rollout can take some of the anxiety out of such a major shift, and helps to get the team used to the changes. This also means that people can learn the process in a more natural way, as a team and in small tasks. The culture change is harder to address but continuous integration fosters a spirit of collaboration amongst developer teams, and should ultimately be beneficial in the long run.

Problem: Continuous integration and continuous deployment are frequently misunderstood. Some businesses confuse or interlink continuous integration with continuous deployment. They are two separate processes and continuous integration does not automatically need to be deployed. Continually updating software may not be right for all companies and can even be a problem. While continuous integration ensures that the base code is always ready to be deployed, it does not mean that it necessarily needs to be.

Solution: This resolution for this is primarily education. Once management gains a better understanding of each process, the benefits and whether or not one is right for their business becomes clear.

Problem: Repetitive ongoing processes. There are many time consuming, repetitive processes throughout the development chain. Not only are these tasks frustrating for highly-skilled developers, but they are also prone to errors.

Solution: Automate all possible processes. Largely manually portions of the work such as testing, building, and deployment can be almost completely automated. Automation ensures an error-free process and allows developers to continue creating new software rather than being stuck in a cycle of simple tasks.

Problem: Legacy Code. If there is an existing system with ‘legacy code,’ it is typically a long and involved process to automate testing for that code.

Solution: It’s important to weigh the pros and cons of converting your legacy code. Tasks will still need to be completed and merged, then tested manually. In this instance, it is worth debating whether continuous integration is the right answer for this project.

Getting Started and Scaling Continuous Integration

Often, businesses or software development teams may start small. These small teams can work on isolated parts of code and then have a ‘merge day’, when all finished tasks are merged at the same time. This works best for smaller teams with very defined roles and tasks.

However, as the team gets larger, merge day can rapidly become a stressful and time-consuming task, resulting in a number of conflicts, bugs, and problems. Each developer adding their work compounds the problem, so identifying where the conflicts and errors arise is difficult.

Pillars of Continuous Integration

Continuous integration is built around a number of other software best practices. It encompasses techniques such as automated testing, build automation, version control, and automated deployments. Each of these has its own ecosystem of philosophies and tools, which will be explored below.

Version Control Management

Version control is a vital pillar of continuous integration. Management of the version source communicates and resolves conflicts between developers simultaneously working on the same base of code.

Automated Testing

Any software project needs thorough and repeated testing. This can be hugely time consuming and repetitive, so tools have been developed to automate parts of the testing process. These testing tools automatically run test cases on specific parts of the system. When a developer pushes code through to the repository, that will trigger the automated testing to start.

Build Automation

Builds are often referred to as the snapshot of the current release module. These builds are what eventually get distributed to the end users via a number of different potential channels. Continuous integration tools help to streamline the process of building a release. Build automations can also set up releases to be triggered by certain events. For instance, when a new piece of code is merged into the production branch of the codebase, it triggers the automation of the upload of the build to a remote server, where users can access and download it.

Automated Deployments

Each deployment process is different depending on what is being built. For example, automated software will deploy a web page to a web server. The build created in the previous step will be automatically copied onto web servers for a web project, uploaded to a store for an app update, as well as any other channels it needs to be deployed on.

Continuous Integration is the Key to Successful Software Development

Continuous integration is important because it helps both Agile development teams and businesses to meet their goals by creating an environment that encourages collaboration and a more robust and reliable software through thorough, regular testing and fast, accurate bug fixes.