What Is a Toggle?

A toggle is a switch that can be turned on and off. It is used in many hardware and software applications to switch between two settings or preferences. For example, the Caps Lock key and Num Lock key on a keyboard are toggle switches that allow users to turn a function on or off.

Toggle Configuration & Testing

When testing a new release, it is important to test all the feature toggle configurations that will be live in production. This is because if the toggles change on release, it can break existing behavior and potentially introduce unexpected regressions.

Most teams rely on static files for toggle configuration, although this can become cumbersome as the number of servers and versions increase. Some teams move Toggle Configuration into some form of centralized store, often an application DB. This allows system operators, testers and product managers to view and modify toggle configuration.

However, this approach does not provide any dynamic re-configuration capability, so teams using this technique for toggles which can be flipped dynamically are recommended to use a real distributed configuration mechanism instead.

Toggle labelling

Toggle labels should clearly and consistently describe what the control will do when it’s on. They should not be neutral or ambiguous and should be in the same language as the controls on which they are used.

It is also wise to ensure that the labels on a toggle are consistent with the surrounding context and visual cues. For instance, a button with a toggle label that’s in the “Disabled” state should be in a different color and have different text than a similar button with an identical label but which is in the “Hidden” state.

Depending on the complexity of a toggle, it can be useful to add a “reset” handler that clears any data associated with the toggle’s current state. This is a good practice in most cases, but it’s especially useful for toggles which affect data stored in external systems or the local filesystem.

Experiment Toggles

A common use of toggles is for experimentation purposes, such as multivariate testing or A/B testing. In these cases the toggle routes that send a user down one codepath or the other are exercised at runtime to see which path has a greater impact on their aggregate behavior.

Because of this, it’s essential to have some way of re-configuring a toggle at runtime in order to avoid any unforeseen results. This means providing a mechanism for the feature flag’s configuration to be overridden as required, which can be done at build time or during testing.

Toggle Override – Dynamic In Memory Config

Another technique for controlling toggle configuration at runtime is the use of a dynamic in-memory configuration system. This is a very powerful tool, but it can be difficult to manage at scale.

Fortunately there are several methods which can be used to achieve this dynamic in-memory re-configuration. These methods range from very simple to highly sophisticated. Some of these techniques require a lot of additional code, but they all offer very compelling benefits.