ASP.NET Core Feature Flags

ASP.NET Core提供了一種動態打開或關閉功能的解決方案。

Nuget Package

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Microsoft.FeatureManagement
Microsoft.FeatureManagement.AspNetCore

Registration

IServiceCollection 服務註冊

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public void ConfigureServices(IServiceCollection services)
{
    services.AddFeatureManagement();
          
    services.AddControllersWithViews();
}

appsetting.json設定

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{ 
    "FeatureManagement":
    {
        "FeatureToggle": true,
        "ActionFilter": true,
        "MiddlewareFilter": true
    }
}

Consumption

Use FeatureManager

  • 建構子注入IFeatureManager介面，調用IsEnabledAsync方法，確認功能是否啟用。
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public class HomeController : Controller
{
    private readonly IFeatureManager _featureManager;
    
    public HomeController(IFeatureManager featureManager)
    {
        this._featureManager = featureManager;
    }
    
    public async Task<IActionResult> FeatureToggle()
    {
        bool isEnabled = await this._featureManager.IsEnabledAsync("FeatureToggle");
        return Content(isEnabled);
    }
}

Use FeatureGateAttribute

  • 針對Controller及Action可以使用FeatureGateAttribute，達到控制是否啟用該功能
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[FeatureGate("ActionFilter")]
public IActionResult ActionFilter()
{
    return Content("Home.ActionFilter");
}

Use MiddlewareForFeature

  • 針對middleware想要做到是否啟用，可以使用IApplicationBuilder擴充方法UseForFeature或是UseMiddlewareForFeature
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public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
       
    app.UseForFeature("MiddlewareFilter", appBuilder =>
    {
        appBuilder.UseHealthChecks("/health");
    });       
}

進階應用

FeatureFilter

依照條件啟動功能標記，Microsoft.FeatureManagement提供內建三種IFeatureFilter實作。

1.PercentageFilter 百分比功能標記

依照百分比的機率啟動功能標記

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{
  "FeatureManagement": {
    "FeatureA": {
      "EnabledFor": [
        {
          "Name": "Percentage",
          "Parameters": {
            "Value": 50
          }
        }
      ]
    }
  }
}

Startup.cs 服務註冊

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public class Startup
{
  public void ConfigureServices(IServiceCollection services)
  {
      services.AddFeatureManagement()
              .AddFeatureFilter<PercentageFilter>();
  }
}

TimeWindowFilter 時間功能標記

在指定時間內啟動功能標記

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{
  "FeatureManagement": {
    "FeatureB": {
      "EnabledFor": [
        {
          "Name": "TimeWindow",
          "Parameters": {
            "Start": "Wed, 01 May 2023 13:59:59 GMT",
            "End": "Mon, 01 July 2023 00:00:00 GMT"
          }
        }
      ]
    }
  }
}

Startup.cs 服務註冊

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public class Startup
{
  public void ConfigureServices(IServiceCollection services)
  {
      services.AddFeatureManagement()
              .AddFeatureFilter<TimeWindowFilter>();
  }
}

TargetingFilter 定位受眾功能標記

在指定目標對象啟動功能標記，在Github有更詳細的說明。https://github.com/microsoft/FeatureManagement-Dotnet/blob/main/README.md#Targeting

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{
  "FeatureManagement": {
    "FeatureB": {
      "EnabledFor": [
        {
          "Name": "Microsoft.Targeting",
            "Parameters": {
                "Audience": {
                    "Users": [
                        "Jeff",
                        "Alicia"
                    ],
                    "Groups": [
                        {
                            "Name": "Ring0",
                            "RolloutPercentage": 100
                        },
                        {
                            "Name": "Ring1",
                            "RolloutPercentage": 50
                        }
                    ],
                    "DefaultRolloutPercentage": 20
                }
            }
        }
      ]
    }
  }
}

還要額外去實作ITargetingContextAccessor.csInterface

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/// <summary>
/// Provides an implementation of <see cref="ITargetingContextAccessor"/> that creates a targeting context using info from the current HTTP request.
/// </summary>
public class HttpContextTargetingContextAccessor : ITargetingContextAccessor
{
    private const string TargetingContextLookup = "HttpContextTargetingContextAccessor.TargetingContext";
    private readonly IHttpContextAccessor _httpContextAccessor;

    public HttpContextTargetingContextAccessor(IHttpContextAccessor httpContextAccessor)
    {
        _httpContextAccessor = httpContextAccessor ?? throw new ArgumentNullException(nameof(httpContextAccessor));
    }

    public ValueTask<TargetingContext> GetContextAsync()
    {
        HttpContext httpContext = _httpContextAccessor.HttpContext;

        //
        // Try cache lookup
        if (httpContext.Items.TryGetValue(TargetingContextLookup, out object value))
        {
            return new ValueTask<TargetingContext>((TargetingContext)value);
        }

        ClaimsPrincipal user = httpContext.User;

        List<string> groups = new List<string>();

        //
        // This application expects groups to be specified in the user's claims
        foreach (Claim claim in user.Claims)
        {
            if (claim.Type == ClaimTypes.GroupName)
            {
                groups.Add(claim.Value);
            }
        }

        //
        // Build targeting context based off user info
        TargetingContext targetingContext = new TargetingContext
        {
            UserId = user.Identity.Name,
            Groups = groups
        };

        //
        // Cache for subsequent lookup
        httpContext.Items[TargetingContextLookup] = targetingContext;

        return new ValueTask<TargetingContext>(targetingContext);
    }
}

Startup.cs 服務註冊

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public class Startup
{
  public void ConfigureServices(IServiceCollection services)
  {

    services.AddSingleton<ITargetingContextAccessor, HttpContextTargetingContextAccessor>();

    services.AddFeatureManagement();
            .AddFeatureFilter<TargetingFilter>();
  }
}

自訂FeatureFilter

針對複雜情形可以自己去實作IFeatureFilter，達到符合特定條件啟用功能。

appsetting.json設定

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{ 
    "FeatureManagement":
    {
        "RequestFilter": {
            "EnabledFor": [
            {
                "Name": "RestrictRequest",
                "Parameters": {
                    "WhiteListIps": [   
                        ],
                    "RestrictPaths": [                  
                    ]
                }
            }]
        }
    }}

需要建立類別實作IFeatureFilter介面

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[FilterAlias("RestrictRequest")]
public class RequestFilter : IFeatureFilter
{
    private readonly IHttpContextAccessor _httpContextAccessor;

    public RequestFilter(IHttpContextAccessor httpContextAccessor)
    {
        _httpContextAccessor = httpContextAccessor;
    }
    
    public Task<bool> EvaluateAsync(FeatureFilterEvaluationContext context)
    {
        var httpContext = this._httpContextAccessor.HttpContext;
        var requestFilterOption = context.Parameters.Get<RequestFilterSetting>();
        var request = httpContext.Request;

        var isPathInRestricts = requestFilterOption.RestrictPaths.Any
        (
            restrictPath => request.Path.StartsWithSegments
            (
                $"/{restrictPath}",
                StringComparison.OrdinalIgnoreCase
            )
        );
        
        if (isPathInRestricts.Equals(true))
        {
            var clientIp = // your ip;

            var ipAddress = httpContext.Connection.RemoteIpAddress.MapToIPv4().ToString();

            ipAddress = string.IsNullOrWhiteSpace(clientIp)
                ? ipAddress
                : clientIp;

            var isIpInWhiteList = requestFilterOption.WhiteListIps.Any
            (
                whiteListIp => ipAddress.StartsWith(whiteListIp)
            );
            
            return Task.FromResult(isIpInWhiteList);
        }

        return Task.FromResult(true);
    }
}

Startup.cs 服務註冊

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public void ConfigureServices(IServiceCollection services)
{
    services.AddHttpContextAccessor();
    
    services.AddFeatureManagement()                 
            .AddFeatureFilter<RequestFilter>();
             
    services.AddControllersWithViews();
}

使用上可用IFeatureManager或是FeatureGateAttribute

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[FeatureGate("RequestFilter")]
public IActionResult RequestFilter()
{
    return Content("Home.RequestFilter");
}