iOS Continuous Integration: How To Avoid Merge Hell

Continuous integration is the software practice where small code changes are frequently tested with the rest of the code to ensure nothing breaks as changes. It makes building and deploying an app easy.

The practice is a response to teams of developers making big changes to the code. Often times, teams are working on the code without testing it. As a result, this breaks lots of functionality, making development slow and painful. 

This post is a brief introduction to Continuous Integration and how that works when building apps for iOS. I will also cover how you and your team can get started. Additionally, this includes building or maintaining your iOS app cheaper and faster.


Listen to our episode with Kyle Newsome on Continuous Integration to learn more


Continuous Integration Is About Reducing The Cost of Change

Continuous Integration (CI) is designed to help you and your developers. For instance, CI helps avoid that painful moment after everyone has written changes or fixes to your app. As a result, everything needs to b integrated back into the code. In particular, this is known as a merge. Eventually, you discover there are now bugs, errors and conflicts created between the different changes.

As you might imagine, it is messy and unpleasant to untangle the code causing problems and fix them. For developers, this is known as merge hell.  For a business that needs the app, it makes any changes very expensive, both in money and time.

CI avoids this problem by requiring developers to write, test, and merge lines of code as rapidly as possible. The original proponents of CI suggested developers merge their code at least once a week. However, daily integration is the most common practice, with some companies, like Netflix, integrating many times a day. The result is that changes happen quickly and if any problems are found, they are small and easy to fix.

There are also a number of additional benefits that CI can bring:

Reduce over-reliance on specific tools, services or individuals

Because CI forces you to make sure everything works constantly on a single source of code, it will quickly expose any ways that prevent you from doing this. This ensures that your app will run on your customers’ machines. As a result. this prevents issues where things will only work with specific tools.

If it can be automated, it will be automated

Core to practicing CI is being able to fully automate all the tests needed to ensure a piece of code will work and automate the deployment process itself. It isn’t possible to merge code on a daily basis without this level of automation. The results should be your developers spending as little time as possible testing and merging their code.

Faster feedback

By integrating code often, you get feedback in the smallest amount of time possible. As a result, this allows you to quickly discover if something works or not.

Helps improve your business

The above doesn’t just apply to writing code; it also allows you to rapidly test how your app works on a business-use level:

  • Do your customers like a new feature or not?
  • Are they having any difficulties purchasing your products?
  • Are they using the app in any unexpected ways?

CI can help you answer these questions quickly and help you create a better experience for them.

How does the App Store fit in with Continuous Integration on iOS?

Continuous Integration & iOS

Practicing with CI when building iOS apps is the same as with any other platform, but Apple does make things a little more difficult. These are relatively easy to overcome but are worth identifying.

The primary obstacle to practicing CI is Apple’s review process. For instance, if you want to deploy code multiple times a day. With Apple’s review process, it ends up being difficult to get your app into the App Store that often. However, if the code change is in a test phase as opposed to production, the review times can be negligible. That is to say, if you use a service like Apple’s TestFlight, then the deploy meant can be immediate.

Often, when you have conflicts in an iOS app, they are small but important. For example, you can forget to update a build number (easily forgettable), or not have the right certificates or profiles set up.

Ultimately, Apple simply requires you to deploy apps in a very specific way. Some of it can be automated, but some can’t. This will mean you may need more time than developing apps for other platforms.

Runners getting started

How to get started using Continuous Integration

One of the best parts of CI is that it is straightforward to get started with it. You only really need a few things to get started: 

Make Sure Your Developers Have All The Same Things

What I mean here is if one developer has a tool or something that is needed to build and test code for your app, ALL the developers should have it. Part of being able to practice CI is being able to reproduce everything your app does on any of your machines. Otherwise, it produces a dependency and will slow everything down.

One Source Of Code Only

In order for CI to work, developers must be working off a single source of code for your app, known as a repository. All code merges are made to this single source. This avoids any confusion and ensures any changes made are only to the most version of your app.

Fully Automate Your Tests

This is absolutely essential for CI. That is to say, an automated testing environment can run thousands of tests in a matter of minutes. (In contrast, it would take hours or days for a human to do manually). As a result of automating your environment, you quickly find out if there are any problems with any change. A point often overlooked but if you don’t have this already, it may take some effort to set up. However, it will easily pay for itself in the time and money it will save you. 

There are some excellent services available to help you automate all your testing in the cloud. Some of the most popular ones are BitRise, Travis CI, and Circle CI. Additionally, there’s Fastlane, a software tool for automating the iOS deployment process.

Get A Code Review Process

Along with developing a process for all your testing, there should be a process for ensuring code has been reviewed before it is merged. This ensures that someone is checking for mistakes and also giving feedback to the developers. It is a simple way of catching problems early so you don’t have to deal with them later. Online services like GitHub have mechanisms for this built in, known as a pull request process, which requires someone to approve any changes a developer has submitted.

Know Who’s Responsible

Related to the above, you often won’t want everyone involved to have the same level of authority or access – you shouldn’t have a developer that can make changes without anyone else having to approve them. This is less about the technology involved and more about the people. Who is responsible for what, and if a mistake is made, who finds out and delivers the feedback necessary to fix it? Ideally, you should figure out everyone’s roles and responsibilities before you start.


Listen to our episode with Kyle Newsome on Continuous Integration to learn more


CI Makes Having An App Cheaper, Faster, & Easier

Continuous Integration is a very useful practice for making building, updating and maintaining an app relatively painless. While it won’t solve problems for you, it makes problems visible so you can solve them for yourself. In the end, CI prevents future issues in the long term.

It is normal to experience friction between the people and tools involved in developing your app, but with a little patience, the gains in productivity can be huge. As a result, your team has created an app and a process with faster builds, easier management, and fewer costs. 

If you’d like to learn more about setting up CI for Swift and iOS development, check out our article on Swift package continuous integration. Also if you’d like to keep up to date with what’s new for iOS and Apple development, I invite you to sign up for my newsletter. I will let you know when I put out new content and if there are important things you should know when it comes to creating or updating your apps.


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