Azure Web Job中Hosted Service作用域异常：本地报错云端正常

我正在开发一个发布为Azure Web Job的BackgroundService，发现一处异常：该服务在Azure上运行正常，但本地运行时会抛出错误。

复现场景代码 #

Program.cs

using TestBackgroundJob;

IHost host = Host.CreateDefaultBuilder(args)
    .ConfigureServices(services =>
    {
        services.AddScoped<IDummyService, DummyService>();
        services.AddHostedService<Worker>();
    })
    .Build();

await host.RunAsync();

Worker类

public class Worker : BackgroundService
{
        private readonly ILogger<Worker> _logger;
        private readonly IDummyService _dummyService;

        public Worker(ILogger<Worker> logger, IDummyService dummyService)
        {
            _logger = logger;
            _dummyService = dummyService;
        }

        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
        {
            while (!stoppingToken.IsCancellationRequested)
            {
                _logger.LogInformation("Worker running at: {time}", DateTimeOffset.Now);
                await Task.Delay(1000, stoppingToken);
            }
        }
}

本地运行错误 #

Cannot consume scoped service 'TestBackgroundJob.IDummyService' from singleton 'Microsoft.Extensions.Hosting.IHostedService'.)'

我怀疑在Azure环境中Worker的作用域从单例变为了Scoped，请问实际情况是否如此？

Worker在Azure Web Job环境中依然是单例服务，并没有被改为Scoped。云端不报错的原因是Azure Web Job的宿主环境在服务注入时，未启用本地Generic Host默认的严格作用域验证逻辑，从而绕过了该错误。

但这种写法不符合依赖注入的作用域规范，会导致Scoped服务的生命周期被强制延长至单例级别，可能引发资源泄漏、状态不一致等潜在问题。正确的做法是通过IServiceScopeFactory在需要时创建作用域来获取Scoped服务，修改后的Worker代码如下：

public class Worker : BackgroundService
{
        private readonly ILogger<Worker> _logger;
        private readonly IServiceScopeFactory _scopeFactory;

        public Worker(ILogger<Worker> logger, IServiceScopeFactory scopeFactory)
        {
            _logger = logger;
            _scopeFactory = scopeFactory;
        }

        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
        {
            while (!stoppingToken.IsCancellationRequested)
            {
                _logger.LogInformation("Worker running at: {time}", DateTimeOffset.Now);
                
                // 创建作用域并获取Scoped服务
                using (var scope = _scopeFactory.CreateScope())
                {
                    var dummyService = scope.ServiceProvider.GetRequiredService<IDummyService>();
                    // 执行dummyService相关操作
                }
                
                await Task.Delay(1000, stoppingToken);
            }
        }
}

该写法能在本地和Azure Web Job环境中均遵循依赖注入的作用域规则，避免潜在风险。

内容的提问来源于stack exchange，提问作者Florin Ghisa