azure - ASP.NET Core BackgroundService 运行多次

Question

我目前有一个带有 .NET Core SDK v5.0.403 的 ASP.NET Core 应用程序。

在此应用程序中，我定义了多个 BackgroundService，其中之一如下:

public class DueDateNotificationService : BackgroundService
{
    private readonly ILogger _logger;
    private readonly IServiceScopeFactory _serviceProvider;

    private readonly int _actionDueDateGenerationDelay;
    private readonly int _startupDelayInSeconds;

    protected static int instances = 0;

    public DueDateNotificationService(ILogger<DueDateNotificationService> logger,
        IServiceScopeFactory serviceProvider,
        IConfiguration configuration)
    {
        _logger = logger;
        _serviceProvider = serviceProvider;

        _actionDueDateGenerationDelay = configuration["BackgroundServices:DueDateNotificationService:DueDateGenerationDelay"].ToInt(240);
        _startupDelayInSeconds = Math.Max(configuration["BackgroundServices:DueDateNotificationService:StartupDelayInSeconds"].ToInt(), 60);
    }

    /// <summary>
    /// Service execution
    /// </summary>
    /// <param name="stoppingToken"></param>
    /// <returns></returns>
    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        // Adding basic data to the logging context
        using (LogContext.PushProperty("AppName", "Api-DueDateNotificationService"))
        {
            _logger.LogInformation("DueDateNotificationService Hosted Service is starting.");
            await Task.Delay(TimeSpan.FromSeconds(_startupDelayInSeconds), stoppingToken);

            
                while (!stoppingToken.IsCancellationRequested)
                {


                    try
                    {
                        using (var scope = _serviceProvider.CreateScope())
                        {
                            var service = scope.ServiceProvider.GetRequiredService<IMyService>();
                            _logger.LogInformation($"doing stuff");
                            service.DoStuff();

                        }
                        // waiting until we should check again
                        _logger.LogInformation($"Job finished at {DateTime.UtcNow}. Next job at {DateTime.UtcNow.AddMinutes(_actionDueDateGenerationDelay)}");
                        await Task.Delay(TimeSpan.FromMinutes(_actionDueDateGenerationDelay));
                    }
                    catch (TaskCanceledException)
                    {
                        _logger.LogWarning("The DueDateNotificationService Hosted Service was cancelled, likely because the site was shutdown (possibly due to inactivity or a force update)");
                    }
                    catch (Exception ex)
                    {
                        _logger.LogError(ex, $"Error occurred executing the automated DueDateNotificationService service.");
                    }
                }
            
            _logger.LogInformation("DueDateNotificationService Hosted Service is stopping.");
        
    }
}

我的服务仅在startup.cs中的一个位置添加到DI:

EnableHostedService<DueDateNotificationService>(services, "BackgroundServices:DueDateNotificationService:Enabled");

EnabledHostedService 为:

private IServiceCollection EnableHostedService<T>(IServiceCollection services, string configurationKey) where T : class, IHostedService
        {
            // Background services to run
            if (Configuration[configurationKey].Equals("true", StringComparison.OrdinalIgnoreCase))
            {
                return services.AddHostedService<T>();
            }

            return services;
        }

这是我注册backgroundService的唯一地方，除了默认提供的之外，应用程序中的任何地方都没有autofac或自定义DI。

我的问题是，每当我的应用程序托管在 azure 应用程序服务中时，所有后台服务都会同时运行多次。

当我查看我的日志时，

DueDateNotificationService Hosted Service is starting.

至少显示两次，我的 while 循环中的所有日志也是如此(我在此处将其删除以减轻帖子的负担)。

但是当我在本地调试它时，它只运行一次，这是应该的。

当我评论我的注册行时，它根本没有启动(即使在 Azure 上)。

它可能来自什么？

谢谢

更新我什至尝试过类似的东西:

protected static int instances = 0;
                ....
                Interlocked.Increment(ref instances);
                if (instances > 1)
                {
                    _logger.LogInformation("An instance of DueDateNotificationService is already started.");
                }
                else
                {
                     MyWhileLoop();
                }

仍然启动/执行多次，日志如下:

An instance of DueDateNotificationService is already started.

从不出现。

Answer 1

azure app service

这几乎肯定是由于您的应用程序正在运行多个实例。

What would be the safest way to have the backgroundservice running only once, beside going through some data persist / check in DB?

外部“租赁”是最安全的方法。您可以使用 CosmosDb/Redis 作为后端自行构建一个，也可以使用内置方法，将 Web 应用程序中的后台服务分解为 Azure WebJob 或 Azure Function。这两个服务都自动使用租约来执行计时器触发的作业。