CommunityToolkit.Aspire.Hosting.Flagd

CommunityToolkit.Aspire.Hosting.Flagd

A .NET Aspire hosting integration for flagd, a feature flag evaluation engine that provides a ready-made, open source, OpenFeature-compliant feature flag backend system.

Getting started

Prerequisites

• .NET 8.0 or later
• Docker (for running the flagd container)

Installation

Install the package by adding a PackageReference to your AppHost project:

<PackageReference Include="CommunityToolkit.Aspire.Hosting.Flagd" />

Usage

In your AppHost project, call the AddFlagd method to add flagd to your application with a flag configuration file:

var builder = DistributedApplication.CreateBuilder(args);

var flagd = builder
    .AddFlagd("flagd")
    .WithBindFileSync("./flags/")
    .WithLogging();

builder.Build().Run();

The fileSource parameter specifies the path to your flag configuration file on the host machine, which will be mounted into the flagd container.

Important: The flagd requires a Sync to be configured. You can use the WithBindFileSync method to configure a file sync. The ./flags/ path is the default path where the flag configuration file is expected to be found. You can change this path to match your configuration.

Configuration

Configuring logging

You can enable the logging for flagd:

var flagd = builder
    .AddFlagd("flagd")
    .WithBindFileSync("./flags")
    .WithLogging();

Customizing the port (flagd endpoint)

You can specify a custom port for the flagd HTTP endpoints:

var flagd = builder.AddFlagd("flagd", port: 9090);

If no port is specified, the default port 8013 will be used.

Customizing the port (OFREP endpoint)

You can specify a custom port for the OFREP HTTP endpoints:

var flagd = builder.AddFlagd("flagd", ofrepPort: 9090);

If no port is specified, the default port 8016 will be used.

Flag Configuration Format

flagd uses JSON files for flag definitions. Please refer to the official documentation for more information. You can create a folder named flags in your project root and place your flagd.json file inside it. It is mandatory for the flag configuration file to be called flagd.json.

Here's a simple example:

{
    "$schema": "https://flagd.dev/schema/v0/flags.json",
    "flags": {
        "welcome-banner": {
            "state": "ENABLED",
            "variants": {
                "on": true,
                "off": false
            },
            "defaultVariant": "off"
        },
        "background-color": {
            "state": "ENABLED",
            "variants": {
                "red": "#FF0000",
                "blue": "#0000FF",
                "yellow": "#FFFF00"
            },
            "defaultVariant": "red",
            "targeting": {
                "if": [
                    {
                        "===": [
                            {
                                "var": "company"
                            },
                            "aspire"
                        ]
                    },
                    "blue"
                ]
            }
        },
        "api-version": {
            "state": "ENABLED",
            "variants": {
                "v1": "1.0",
                "v2": "2.0",
                "v3": "3.0"
            },
            "defaultVariant": "v1"
        }
    }
}

Additional Information

For more information about flagd, visit the official documentation.

To use flagd in your application, you'll need to install an OpenFeature provider for .NET. See the OpenFeature .NET documentation for details.