Continuous Integration Tools - Leading Solutions

Just a little more than a decade ago, development cycles were very different than they are today. Developers worked more independently, and they were often responsible for their own builds. Integration of the end product's various features didn't happen until the end of the cycle. In hindsight, that sounds counter-intuitive considering all that can go wrong during the integration process. Such unforeseen challenges frequently created chaos for production schedules. It makes more sense for developers working together on one project to continuously integrate their code into a shared repository, and then address issues as they arise. That's the concept of continuous integration or CI.

As a practice, continuous integration just means encouraging developers to constantly integrate their code into a shared repository throughout the development cycle. Preferred strategies have shifted over the years, and virtually all integration processes can now be automated thanks to continuous integration tools. Nonetheless, you should know a little bit about what those tools actually do.

This guide will cover the basics of continuous integration and provide an overview of the best continuous integration tools on the market.

What are the benefits of continuous integration?

Continuous integration came about as an effort to lower costs and speed up production. Tackling integration issues throughout the development cycle rather than waiting until the end helps production teams better anticipate time and budget considerations. It also helps developers, IT teams and project managers to work more efficiently.

Of course, continuous integration by itself doesn't ensure that an app will work perfectly or at all. Roadblocks are always inevitable. The earlier continuous integration is implemented, however, the greater the benefits you can reap. Conversely, identifying conflicts between new and existing code gets more difficult the longer you put off integration. Like most problems in life, coding conflicts compound exponentially over time, so addressing them head on is an advisable strategy.

Some organizations still handle integration mostly manually. Developers are responsible for making sure that new code meets standards and doesn't hinder existing functionality, which costs both time and money. Fortunately, there are dozens of test suites and automated systems that can take care of those tasks. Developers can just merge code into the main repository and wait to be alerted when problems are detected by their continuous integration tools.

Introducing continuous integration tools

Continuous integration tools automate the tedious jobs of building software, running tests against it and getting it packaged for deployment. They can provide the entire development team with rapid and regular feedback. With the right set up, you can know within minutes if the code you just created is compatible with everyone else's, and everyone will have access to the results in a single central location. Such fast feedback cycles perfectly fit the agile web development workflow.

The history of continuous integration

Back in the early 2000s, developers working together as a team would each receive their own copies of the source code and be left to figure out how to handle their own builds. That's no problem for most developers, but it's a terribly inefficient way to create a cohesive end product. Even if they are working from the same code, developers may have different versions of external libraries, or they may use folder structures that impact how the software runs. As you can imagine, ironing out those inconsistencies consumed a lot of time.

Builder servers were eventually introduced so that everyone's code could be kept in one central location, and weekly builds became a normal practice. Weekly builds became nightly builds, and the idea of automating the entire build process became popular as development teams saw the benefits of iterative integration. Automation scripts evolved and proliferated, and early continuous integration tools like Apache Ant arrived on the scene.

The advent of agile development popularized frequent unit testing, and nightly builds weren't providing fast enough feedback cycles. Although the concept of continuous integration was initially met with resistance by some, it soon became necessary to meet production deadlines. A market of continuous integration tools soon emerged out of the ever increasing demand for quicker feedback.

Continuous integration workflow

Even if you have all of the right continuous integration tools to work with, you should still understand how the process works. Here are the steps of a typical continuous integration workflow:

1. If possible, it's recommended for individual developers to first run builds and unit tests on their own machines before checking in new code to the main repository.
2. When you check in your code, your CI tools should detect changes and begin building. Code is then compiled; if compilation fails, the build will cease, and you'll receive an error message.
3. Once you have a successful build, your CI software runs static analyzers to conduct quality control tests. You can set up some CI tools to fail if the build doesn't meet specified standards.
4. Unit testing is performed against the compiled code, and a report with the results is generated. You can set up email alerts to notify your team when problems occur. Many continuous integration tools also feature a web interface where everyone can view the results of the most recent build.
5. The build is finally packaged for deployment, and tagging may be added to mark the software version. Even though your build should be perfect by this point, some teams then deploy their code directly into an environment where more tests can be conducted by humans.

There are different ways to set up your continuous integration workflow, but the general process always involves creating the build, checking it for problems and preparing for deployment all automatically whenever new code comes in. All that's left for your team to do is to fix any errors that your continuous integration tools detect.

Top continuous integration tools

Now that you know what continuous integration entails, it's time to take a look at some of the tools that make it happen. Below is a list of the leading continuous integration tools available.

1. Jenkins

Jenkins is often considered the top open source option for automating continuous integration thanks to its seemingly endless supply of custom plugins. Whether used as a standalone CI server or as a continuous delivery platform, Jenkins is an all-in-one solution for building projects, running tests, analyzing code, detecting bugs and deployment.

Notable features:

• Thousands of plugins supported
• Pre-built installation packages for Unix, Windows, and OS X
• Convenient web interface for configuring a server
• Deployable across large networks
• Supported by a massive community including major software brands

2. Travis CI

Travis CI is an enterprise solution used by several large web-based companies like Facebook, Mozilla and Twitter. Nonetheless, anyone can easily integrate Travis CI with their GitHub projects. All you have to do is sign up to start testing code.

Notable features:

• Free for open source repositories
• Bilingual support
• Automated pull request verification
• Extended API and CMD tools
• Easy notification setup

3. Codeship

Codeship is a hosted CI platform that offers one-click signup with GitHub, GitLab or Bitbucket. It's easy to customize and automatically scales to meet your needs.

Notable features:

• Native support for Docker instances. Learn more about Docker in our Docker tutorial
• Straightforward config file management
• Simple UI that keeps a history of changes
• Free to use with paid hosting package

4. TeamCity

TeamCity is a one-size-fits-all intelligent CI server created by Jetbrains. Designed with developers in mind, TeamCity lives up to its name by facilitating stronger collaboration. It offers extensive support for Visual Studio including tool versioning, framework testing, code coverage and code analysis with no need for external scripts.

Notable features:

• Several pre-built installers
• Comprehensive version control
• Detailed history reports
• Free and enterprise options

5. CircleCI

With CircleCI, developers have a lot of flexibility for setting up their continuous integration and delivery processes. It has helped countless teams increase their productivity thanks to effortless scaling.

Notable features:

• Custom integration with Maven, Gradle and other build tools
• Grabs custom settings directly from your code
• Easily integrates with cloud platforms like AWS, Heroku, and Google Cloud
• Uses language-specific tools to install dependencies into an isolated environment
• Free and premium options

6. AppVeyor

If you're working on an app exclusively for Windows, AppVeyor may be your best bet.

AppVeyor only works with Windows, but it's among the best continuous integration tools for testing and deploying applications. This cloud based service comes with Visual Studio and several SDKs, so you can have a strong CI environment up and running fairly quickly.

Notable features:

• Very easy to set up with Windows
• Isolated build environments
• SSD drives with dedicated hardware
• Custom team environments with granular methodologies

7. GitLab CI

This code management platform has a clean dashboard that gives you an overview of your project's progress. As its name implies, GitLab CI integrates directly into the GitLab workflow, and each feature comes with detailed documentation.

Notable features:

• Pre-built packages for popular Linux distributions
• Manual deployment with effortless rollback capabilities
• Free community edition with per-user enterprise plans

8. Nevercode

If you don't like coding, then Nevercode was made for you. This highly automated CI tool requires minimal effort. It easily integrates with common app development tools, which makes for a comfortable development experience. The only downside is that Nevercode is exclusively for mobile applications.

Notable features:

• Automatic deployment to app stores
• Custom unit and UI testing with an emulator or hardware
• State-of-the-art encryption
• Several free and premium options to meet a wide range of needs

Continuous integration in action

Jenkins is no doubt the most popular continuous integration tool currently. However, if it happens that Jenkins just isn't the right fit for your setup, we've taken a look at five other tools mentioned in this article and compared them in Google Trends.

Of the five tools selected, Travis CI was the most popular according to Google trends for an extended period of time. However, as of lately, GitLab CI has been gaining in popularity quite quickly.

Continuous integration isn't just a set of tools and procedures; it's more like a mindset. The goal of CI is to incorporate integration into the everyday development workflow, which requires the cultivation of a team culture that encourages responsiveness. Build engineers can put a lot of thought into crafting continuous integration processes, and they may disagree about the most effective strategies; however, with the right attitude and the right continuous integration tools, development teams should agree on a set of standards and tactics that work best for everyone.