LaunchDarkly Developer Documentation

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LaunchDarkly provides feature flags as a service for Java · Python · Ruby · Go · Node.js · PHP · .NET. Control feature launches -- who sees what and when -- without multiple code deploys. Easy dashboard for phased rollouts, targeting and segmenting.
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Prerequisites allow you to control feature dependencies in LaunchDarkly. You can add a list of flags and their expected values as prerequisites to enable a feature.

Let's say we have two flags that control an API: api_reads and api_writes. In this case, it makes no sense to have write access to the API if you do not have read access.

With prerequisites, you can make sure that api_reads is On with the user receiving true before api_writes is evaluated for that user.

You can manage your prerequisites in the feature flag's Targeting tab:

To meet a prerequisite, the prerequisite flag must be On, and the current user must receive the specified variation.

Circular Dependencies

LaunchDarkly will automatically prevent you from saving changes that would introduce circular dependencies between prerequisites.


Note that if flag A has flag B as a prerequisite, then callers relying on flag A need to also include all user attributes needed to evaluate flag B, in addition to any user attributes normally supplied for flag A.

Deleting Flags With Prerequisites

You cannot remove a flag that other flags are dependent on. You must first remove the dependency before the flag can be deleted.