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Feature toggles enable you to test and roll out features in an incremental way. They’re a key part of agile development and testing processes.
A toggle is a boolean variable that is set to either True or False by code. This can be triggered by any event or action, such as a button click or a change in user data. The state of a toggle can then be used to trigger other code in your application, such as changing a color or changing the display layout of an element on a page.
When designing a user interface, toggles can be useful for creating responsive designs by allowing developers to show or hide different elements based on the device or screen size. Toggles can also be used to implement themes in applications.
Using Toggles
It’s best to keep the number of toggles deployed in production as low as possible. Too many can have a negative impact on the performance of your software. A toggle requiring database calls each time it’s flipped or a toggle that is re-deployed frequently can lead to thousands, or even millions of, unnecessary SQL queries in production. It’s also important to have a process in place for pruning old toggles as soon as they are no longer needed. This can be as simple as adding a toggle cleanup task to the team backlog or building the process into your management platform.
Ideally, toggles should be able to be changed at runtime by an automated system. This makes it easy to perform regression tests on your feature flags and helps you get feedback from your users quickly. However, this isn’t always possible. In some cases, it might be necessary to manually update a toggle configuration. For example, if you need to switch a toggle from Off to On for a specific user group, you might need to update the feature’s documentation or run a manual regression test on that specific user.
When testing a feature, it’s important to test the toggle configuration you expect to go live with in production. This usually includes the current production toggle configuration plus any toggles you intend to release flipped On. It’s also a good idea to test the fallback configuration where all toggles are flipped Off. This will help you prevent any surprise regressions if a new feature causes existing or legacy behavior to break in the future. Toggle configurations should generally only be left in place for a short period of time – ideally, less than a week. This is to ensure that they don’t introduce bugs into the production environment that would otherwise be difficult to track down.