A toggle is a switch that has two positions – on or off. You see this kind of switch in hardware like the Caps Lock and Num Lock keys on a keyboard, as well as software when you use a hotkey to alternate between different functions of an application.
In a product context, Toggles can be used to hide features for specific users or groups of users so that they don’t see or interact with the feature. This allows an engineering team to deploy a new feature and then test it in a low-traffic environment before moving it into production where it will have more impact.
Feature Toggles can also be used to perform A/B testing. Toggle switches bucket users into one or the other of a pair of codepaths (with and without a tested feature). Then, at runtime, a Toggle Router consistently sends each user down the appropriate path based on which cohort they belong to. This is a very simple way to perform A/B testing that can be extremely powerful and efficient.
Toggles can also be used for logging and other types of monitoring in an application. They can be set up to log all or no events depending on their state and then later analyzed in order to understand the performance of an application. This can be especially useful when it comes to detecting issues that may not surface in a live production environment but become apparent when running an A/B test.
When designing a Toggle, it is important to remember that a toggle switch should be used sparingly and only when the user must make a choice between two opposing states. Toggles should always be clear and easy to understand and they should be designed with the same care that would go into any other element of a website or application.
There are a number of ways to implement a Toggle, ranging from fairly simplistic approaches that involve hard-coding the configuration in the source code through to more complex approaches that require a specialized back-end system. In general it is preferable to use an approach that supports dynamic in-memory re-configuration of a specific service instance rather than having to manually re-deploy a new version of the application in order to change the toggle configuration.
Toggle is a very useful and powerful tool for managing feature releases but it can be risky in a production environment. Unless you’re working with a tightly controlled and managed deployment environment it is recommended to only use Toggles for experiments that have a short lifecycle, such as an A/B test. This will help reduce the risk of unexpected regressions and enable your engineering team to deliver a high quality product at a faster pace.
