How to schedule a background service to initiate every deployment without a controller action in IIS

Question

I have built out a service to create an erxcel report which uploads to a cloud storage provider. I am creating a scheduled task to occur at midnight every night to run this service. My issue is I often am redeploying my application for updates and all and I am trying to figure out how to get this background task to run every time I redeploy. Can this be done automatically or do I need to create a controller action and manually remember to call it so the task starts?

My code is as follows:

public class ReviewSummaryBackgroundService : BackgroundService
{
    protected IReviewSummaryService _reviewSummaryService;
    
    public ReviewSummaryBackgroundService(IReviewSummaryService reviewSummaryService)
    {
        _reviewSummaryService = reviewSummaryService;
    }
    
    private static int SecondsUntilMidnight()
    {
        return (int)(DateTime.Today.AddDays(1.0) - DateTime.Now).TotalSeconds;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        var countdown = SecondsUntilMidnight();

        while (!stoppingToken.IsCancellationRequested)
        {
            if (countdown-- <= 0)
            {
                try
                {
                    await OnTimerFiredAsync(stoppingToken);
                }
                catch(Exception ex)
                {
                    // in future log exception
                }
                finally
                {
                    countdown = SecondsUntilMidnight();
                }
            }
            await Task.Delay(1000, stoppingToken);
        }
    }

    private async Task OnTimerFiredAsync(CancellationToken stoppingToken)
    {
        await _reviewSummaryService.ExportExcelReportAsync();
    }
}

Answer 1

Assuming you're registering the background service as follows, it will be started when your application starts:

builder.Services.AddHostedService<ReviewSummaryBackgroundService>();

If you want to ensure that the report doesn't get created on each local debugging attempt, but when deployed to your prod environment, you could take advantage of the ASPNETCORE_ENVIRONMENT

public ReviewSummaryBackgroundService(IWebHostEnvironment env, IReviewSummaryService reviewSummaryService) 
{
    _Env = env;
    //...
}

private static TimeSpan TimeUntilMidnight()
{
    return DateTime.Today.AddDays(1) - DateTime.Now;
}

protected override async Task ExecuteAsync(CancellationToken stoppingToken)
{
    var delay = _Env.IsProduction() ? TimeSpan.Zero : TimeUntilMidnight();
    
    while (!stoppingToken.IsCancellationRequested)
    {
        await Task.Delay(delay, stoppingToken);
        
        try
        {
            await OnTimerFiredAsync(stoppingToken);
        }
        catch (Exception ex)
        {
            // in future log exception
        }

        delay = TimeUntilMidnight();
    }
}