Design Challenge 004: Cleaning Up Feature Toggles in a Large Codebase

Welcome to another issue of The Pragmatic Developer! In this edition, we delve into a common but challenging task faced by many developers working in large codebases: cleaning up feature toggles. We'll explore the intricacies of managing feature toggles at scale and the pain points involved in their removal. As always, I encourage you to tackle the challenge on your own before we dive into my solution in the next issue.

Introducing Feature Toggles / Feature Flags

Feature toggles, also known as feature flags, are a powerful technique in software development that allows teams to enable or disable features in a system without deploying new code. By using feature toggles, developers can separate feature rollout from code deployment, enabling continuous delivery and more flexible release strategies. This approach allows for testing features in production with a subset of users, rolling out features gradually, and even turning off features that aren't performing as expected. Essentially, feature toggles give developers greater control over their software, improving agility and reducing risk.

Photo by Louis Reed on Unsplash

Imagine we have a function featureToggle that accepts a string as a feature name and returns either true or false to indicate if that feature is on or off. Managing these feature toggles seems straightforward on the surface. However, consider the scale: with hundreds of features in play, the complexity increases significantly. We might need different toggles to be on or off in various environments, override some of them for specific users, etc. Things quickly become complicated.

Additionally, cleaning a toggle is a labor-intense and error-prone task in large projects. Think of the surrounding changes required when a toggle needs to be removed. We need to look into all the usages, including tests, storybook examples, visual regression tests, and more. Also, imagine we have to do that frequently as we deliver new features.

Manual Removal Process and Challenges

One of the challenges is that we have to analyze all the usages of a feature toggle in the code. Typically, you need to search for all usages and analyze if you need to change them or not. You could use traditional command-line tools like sed or even your IDE to help. But there is code in comments, in markdown docs, and you could use file types to filter out this noise. Even in the code, there could be many cases. For example, consider the following code snippets:

if (featureToggle('feature-x')) {
  // do something interesting
}

or one might prefer to use a ternary expression:

const data = featureToggle('feature-x') ? { foo: 'bar' } : {};

or even combine it with other conditions in if-else:

if (featureToggle('feature-x') && otherFlag && otherCheckFunc()) {
  // do something interesting
}

It's also common for developers to extract a helper function in a certain place:

const isFeatureXEnabled = featureToggle('feature-x');
export { isFeatureXEnabled };

and then import and use it in many places:

import { isFeatureXEnabled } from './toggles';

if (isFeatureXEnabled) {
  // do something interesting
}

Additionally, you might find similar code in your tests to simulate the toggle on and off scenarios:

it('formats title in title case when feature-x is on', () => {
  featureToggle.mockImplementation((feature) => {
    if (feature === 'feature-x') return true;
    return false;
  });

  const title = format("hello world");
  expect(title).toEqual("Hello World");
});

it('formats title in capitalize when feature-x is off', () => {
  featureToggle.mockImplementation((feature) => {
    return false;
  });

  const title = format("hello world");
  expect(title).toEqual("Hello world");
});

The Pain of Removing Feature Toggles at Scale

In short, there are just too many variations of usages. And that's only one feature toggle. Imagine working in a large codebase where at any time there might be 100 feature flags in flight. Now, cleaning them is not a trivial task anymore.

Broader Implications and Challenges

1. Scalability Issues: As the number of feature toggles grows, the complexity of managing them escalates. Keeping track of which toggles are active in different environments can become overwhelming. For large codebases, manually removing toggles can consume significant developer time and effort.

2. Code Bloat and Technical Debt: Feature toggles, if not removed in a timely manner, can lead to code bloat and increase technical debt. Old and unused toggles clutter the codebase, making it harder to read and maintain. This can slow down development and lead to more bugs.

3. Consistency Across Environments: Ensuring that toggles are consistently applied across development, staging, and production environments is crucial. Mismanagement can result in features being accidentally enabled or disabled, causing discrepancies and unexpected behavior.

4. Testing Complexity: Feature toggles add layers of complexity to testing. Test cases need to account for various combinations of toggles being on or off. This increases the number of test scenarios, making it harder to maintain comprehensive test coverage.

5. Risk of Human Error: Manual removal of feature toggles is prone to human error. Developers might miss some instances of the toggle, leading to incomplete removal. This can cause the codebase to behave unpredictably or retain unwanted features.

The Need for Automation

Imagine having a tool that can automatically clean up these toggles (considering there could be hundreds of toggles in a large repository at any given time). Such a tool could:

• Save Time and Effort: Automating the removal process frees up developers to focus on more critical tasks.

• Ensure Consistency: A tool can systematically identify and remove all instances of a feature toggle, ensuring no remnants are left behind.

• Reduce Errors: Automation minimizes the risk of human error, leading to a cleaner and more reliable codebase.

• Maintain Code Quality: By regularly cleaning up feature toggles, the codebase remains clean and manageable, reducing technical debt and improving overall code quality.

The Challenge

Here's the challenge for you: imagine you have to clean up a feature toggle named feature-x from a large codebase. How would you go about doing it? What tools and strategies would you use to catch and handle all instances correctly? Take some time to think about it and maybe even try it on a smaller-scale project.

In the next issue, I'll share my approach to automating this process and the tool I use to make it efficient and error-free.

Thank you for reading this issue of The Pragmatic Developer. I hope you found the discussion on feature toggles and their cleanup insightful. As always, I encourage you to share your thoughts and solutions. Stay tuned for the next issue, where I'll reveal my solution to this challenge. Until then, happy coding!