Skip to main content

How to use the SDK's "evaluation reasons" feature to troubleshoot flag evaluation

Affected: All SDKs

Overview

When using the SDK to evaluate flags, you may receive a value that is unexpected. All SDK events received by LaunchDarkly are processed and then disposed of. LaunchDarkly does not keep a history of flag evaluations, and we cannot conclusively tell you why a flag was evaluated the way it did.

On the surface, the SDK isn't very transparent, and without additional tooling, it's hard to see why the SDK behaves the way it does. This article will go over adding tooling to your implementation in order to troubleshoot unexpected evaluation results.

Solution

To identify why your flags evaluate the way they do, follow these steps:

  1. Implement evaluation reasons into your application. You can read more about this in our docs: Evaluation reasons.

  2. Use our SDK's "evaluation reasons" feature to get the reason information. This can be exposed through logging or reporting to a logging platform.

  3. Reference the following scenarios to investigate unexpected flag evaluation behavior.

Condition

Reason

Solution

Resources
If the kindyou receive is one of:
  • OFF
  • FALLTHROUGH
  • TARGET_MATCH
  • RULE_MATCH
  • PREREQUISITE_FAILED

and you are expecting a different kind or receiving an unexpected variation.

The SDK is likely evaluating flags using a stale cache.

Most SDKs have a future/promise you can use when initializing the SDK or calling the SDKs identify method. You can use this to know when the SDK has finished initializing and, you can evaluate flags using a fresh cache.

Alternatively, you can use our SDK's "Monitoring SDK Status" feature to use a listener pattern to know when the SDK is ready to serve fresh flags.

Initializing the SDK

Identify method

Monitoring SDK status

If the kindyou receive isERROR, and the errorKind is:

  • CLIENT_NOT_READY
  • FLAG_NOT_FOUND
 The SDK is being used before it has a chance to populate the cache for the first time.

If the kindyou receive isERROR, and the errorKind is:

  • USER_NOT_SPECIFIED
 A null context was provided to the SDK. Ensure you're providing a valid context to the SDK.

Initializing the SDK

Identify method

If the kindyou receive isERROR, and the errorKind is:

  • WRONG_TYPE

The wrong variation method is being called. LaunchDarkly SDKs for type-strict languages provide several different variation methods.

For example, if you have a flag that serves boolean variations and the stringVariation method is used, you will get this error.

 Ensure you're evaluating flags using the correct method.

SDK API Documentation

If the kindyou receive isERROR, and the errorKind is:

  • MALFORMED_FLAG
  • EXCEPTION
 An unexpected error occurred. Reach out to LaunchDarkly Technical Support for assistance.

Contact Technical Support

 

 

 

Was this helpful?