Feature filter from second configuration source is not respected when the base configuration does not specify a filter

[robertvandiest]

I have run into something yesterday that cost me quite a bit of time and headache to figure out, and is incorrect behavior in my opinion.

If I specify the following feature flag in my appsettings.json:

  "FeatureManagement": {
    "Manage_Folders": true
  }

And override this value in Azure App Configuration with:

{
    "id": "Manage_Folders",
    "description": "Enable folder management",
    "enabled": true,
    "conditions": {
        "client_filters": [
            {
                "name": "Microsoft.Targeting",
                "parameters": {
                    "Audience": {
                        "Users": [],
                        "Groups": [],
                        "DefaultRolloutPercentage": 50
                    }
                }
            }
        ]
    }
}

This does not work as expected, as the filter is never evaluated and the feature is turned on for 100% of the requests.

In other situations, the behavior is correct and the filter is evaluated using the values supplied in Azure App Configuration:

1. Situation 1: toggle set to false

appsettings.json

  "FeatureManagement": {
    "Manage_Folders": false
  }

Azure App Configuration:

{
    "id": "Manage_Folders",
    "description": "Enable folder management",
    "enabled": true,
    "conditions": {
        "client_filters": [
            {
                "name": "Microsoft.Targeting",
                "parameters": {
                    "Audience": {
                        "Users": [],
                        "Groups": [],
                        "DefaultRolloutPercentage": 50
                    }
                }
            }
        ]
    }
}

2. Situation 2: A filter is also specified in appsettings.json, which is correctly overridden by the values from Azure App Configuration

appsettings.json

  "FeatureManagement": {
    "Manage_Folders": {
      "EnabledFor": [
        {
          "Name": "Percentage",
          "Parameters": {
            "Default": "0"
          }
        }
      ]
    }
  }

Azure App Configuration:

{
    "id": "Manage_Folders",
    "description": "Enable folder management",
    "enabled": true,
    "conditions": {
        "client_filters": [
            {
                "name": "Microsoft.Targeting",
                "parameters": {
                    "Audience": {
                        "Users": [],
                        "Groups": [],
                        "DefaultRolloutPercentage": 50
                    }
                }
            }
        ]
    }
}

Currently I managed to find a workaround for my usecase, but this behavior is incorrect in my opinion.

[jimmyca15]

Hello @robertvandiest

I agree with your sentiment. This concern is also detailed in this previous issue: https://github.com/microsoft/FeatureManagement-Dotnet/issues/74.

I'd like to continue the conversation there if possible.

I would say the issue is a bit tricky here, and I'd like to know if you can provide the scenario that motivates you to do this to help see if it can drive a solution. The issue arises due to how .NET core configuration system works, which is a layer underneath this library.

I will close this issue in hopes that we can continue in the existing issue thread.