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Troubleshooting flagd

Debugging Evaluations

If a flag or targeting rule isn't proceeding the way you'd expect, you may want to enable more verbose logging.

flagd and flagd providers typically have debug or verbose logging modes that you can use for this sort of troubleshooting. You can do this in the standalone version of flagd by starting it with the --debug flag (see CLI for more information).

In-process providers which embed the flag evaluation engine use a logging consistent with their implementation language and SDK. See your provider's documentation for details on how to enable verbose logging.

The detailed evaluation functions can also be helpful in understanding why an evaluation proceeded a particular way.

HTTP Integer Response Behavior

Why is my int response a string? Command:

curl -X POST "localhost:8013/flagd.evaluation.v1.Service/ResolveInt" -d '{"flagKey":"myIntFlag","context":{}}' -H "Content-Type: application/json"



When interacting directly with the flagd HTTP api and requesting an int the response type will be a string. This behaviour is introduced by grpc-gateway, which uses proto3 json mapping to build the response object. If a number value is required, and none of the provided SDK's can be used, then it is recommended to use the float64 endpoint instead:


curl -X POST "localhost:8013/flagd.evaluation.v1.Service/ResolveFloat" -d '{"flagKey":"myIntFlag","context":{}}' -H "Content-Type: application/json"



Extra (Duplicate) Events in File Syncs

When using the file sync, you may notice more events than you'd expect. This is attributable to nuances in text editors and the OS/filesystem. Most editors will cause a few filesystem events on a save, for instance, not just one as you might expect. Additionally, most filesystem operations are not atomic and also will result in multiple events. Generally speaking, updating a symbolic link will result in only a single event, and may even be atomic on your filesystem/OS. In fact, this is how Kubernetes handles changes to mounted ConfigMaps (OpenFeature Operator takes advantage of this fact in it's file mode). It's recommended if you're using the file sync in production, you use a symbolic link for the watched file, and update its contents by changing its target.

Received unexpected EOS on empty DATA frame from server

This error message indicates that HTTP2 requests are being blocked (gRPC runs over HTTP2). You may need to explicitly allow HTTP2 or gRPC in your platform if you're using the sync gRPC service.


HTTP2 is not strictly for the flag evaluation gRPC service, which is exposed both as a gRPC service and a RESTful HTTP/1.1 service, thanks to the connect protocol.