A toggle is a switch that has two positions, either on or off. The concept is familiar to many users from the Caps Lock and Num Lock buttons on their keyboard or from the on/off switch in their TV remote control. The word is also used to describe software and hardware settings that can be flipped between different modes. For example a button that switches between stream and map views in a video chat is often referred to as a toggle.
The term can also refer to any kind of change from one state to another, such as switching from a low battery indicator to an active power indicator. In software development a toggle is often used to describe a switch that can be turned on or off or between different modes such as Canary Release and Champagne Brunch mode.
Toggle configuration can be managed in a variety of ways, from static files through to more sophisticated approaches which involve a specialized re-configuration system. In general it is recommended to avoid any method which requires a change in the source code of the application in order to change the toggle configuration as this can introduce friction in the testing and validation process.
Toggle configuration that is hardcoded into the application can be useful as a way to control the behavior of an entire fleet of servers but this approach is limited by its dependence on the ability to reliably re-deploy the server-side code in order to modify the toggle configuration. To overcome this limitation and to enable true runtime toggle configuration it is usually necessary to implement a re-configuration system which allows for dynamic in memory re-configuration of Feature Flags.