Cloud.Core.FeatureFlag.LaunchDarkly

An implementation of the IFeatureFlag wrapper for the Launch Darkly Client.

Usage

You can explicitly create the Launch Darkly Service with an SDK key as follows:

var ldService = new LaunchDarklyService("Launch Darkly Key");

Or allow the key to be picked up automatically from config:

IConfiguration config = configBuilder.Build();

// looks for the "LaunchDarklySdkKey" key within config.
var ldService = new LaunchDarklyService(config); 

Or you can use the service collection extension as follows:

// With a key directly.
services.AddLaunchDarklyFeatureFlags("Launch Darkly Key");

// With an existing client.
services.AddLaunchDarklyFeatureFlags(new LdClient());

// Or allow it to pickup from config.
services.AddLaunchDarklyFeatureFlags();

This method will then take IConfiguration as an automatically resolved dependency and look for a config value of "LaunchDarklySdkKey" from the configuration. You must ensure it exists! It can be gathered from SecureVault.

NOTE: If used in a web API, a 404 response will be returned. This is to indicate the method or endpoint is not available when the flag is disabled.

Attribute Usage

This can be used in the AppHost or in a WebHost. Using the WebHost as an example, you may want an entire controller to be controlled via a feature flag. That would be done as follows:

[ApiController]
[ApiVersion("1.0")]
[Route("api/v{version:apiVersion}/[controller]")]
[Produces("application/json")]
[FeatureFlag("MigrationsV2")] // ADDED HERE!
[SwaggerResponse(404, "MigrationsV2 feature flag is disabled.", Type = null)]
public class MappingFilesController : ControllerBase
{
    private readonly MigrationsContext _migrationsContext;
    private readonly ILogger<MappingFilesController> _logger;

    public MappingFilesController(MigrationsContext migrationsContext, ILogger<MappingFilesController> logger)
    {
        _migrationsContext = migrationsContext;
        _logger = logger;
    }

    [HttpGet]
    [ProducesResponseType(typeof(IEnumerable<MappingFile>), 200)]
    [SwaggerResponse(200, "Retrieve all items", typeof(IEnumerable<MappingFile>))]
    public async Task<ActionResult<IEnumerable<MappingFile>>> Get() 
    {
        return await _migrationsContext.MappingFiles.ToListAsync();
    }
}

You can also opt to add at method level within the same controller:

[ApiController]
[ApiVersion("1.0")]
[Route("api/v{version:apiVersion}/[controller]")]
[Produces("application/json")]
[SwaggerResponse(404, "MigrationsV2 feature flag is disabled.", Type = null)]
public class MappingFilesController : ControllerBase
{
    private readonly MigrationsContext _migrationsContext;
    private readonly ILogger<MappingFilesController> _logger;

    public MappingFilesController(MigrationsContext migrationsContext, ILogger<MappingFilesController> logger)
    {
        _migrationsContext = migrationsContext;
        _logger = logger;
    }

    [FeatureFlag("MigrationsV2")] // ADDED HERE!
    [HttpGet]
    [ProducesResponseType(typeof(IEnumerable<MappingFile>), 200)]
    [SwaggerResponse(200, "Retrieve all items", typeof(IEnumerable<MappingFile>))]
    public async Task<ActionResult<IEnumerable<MappingFile>>> Get() 
    {
        return await _migrationsContext.MappingFiles.ToListAsync();
    }

    [FeatureFlag("MigrationsV3")] // ADDED HERE!
    [HttpGet("{id}")]
    [ProducesResponseType(typeof(IEnumerable<MappingFile>), 200)]
    [SwaggerResponse(200, "Retrieve specific item", typeof(MappingFile))]
    public async Task<ActionResult<MappingFile>> Get(int id) 
    {
        var item = await _migrationsContext.MappingFiles.FindAsync(x => x.id == id);
        if (item.IsNullOrDefault())
        {
            return NotFound();
        }
        
        return item;
    }
}

Test Coverage

A threshold will be added to this package to ensure the test coverage is above 80% for branches, functions and lines. If it's not above the required threshold (threshold that will be implemented on ALL of the core repositories to gurantee a satisfactory level of testing), then the build will fail.

Compatibility

This package has has been written in .net Standard and can be therefore be referenced from a .net Core or .net Framework application. The advantage of utilising from a .net Core application, is that it can be deployed and run on a number of host operating systems, such as Windows, Linux or OSX. Unlike referencing from the a .net Framework application, which can only run on Windows (or Linux using Mono).

Setup

This package is built using .net Standard 2.1 and requires the .net Core 3.1 SDK, it can be downloaded here: https://www.microsoft.com/net/download/dotnet-core/

IDE of Visual Studio or Visual Studio Code, can be downloaded here: https://visualstudio.microsoft.com/downloads/

How to access this package

All of the Cloud.Core.* packages are published to a public NuGet feed. To consume this on your local development machine, please add the following feed to your feed sources in Visual Studio: https://dev.azure.com/cloudcoreproject/CloudCore/_packaging?_a=feed&feed=Cloud.Core

For help setting up, follow this article: https://docs.microsoft.com/en-us/vsts/package/nuget/consume?view=vsts