IIS托管ASP.NET Core 6 Web API返回结果时客户端挂起排查

在Windows 10系统的IIS 10上部署了基于.NET 6开发的ASP.NET Core Web API应用，服务核心逻辑为调用外部API后将结果返回给调用方，保留关键逻辑的简化代码如下：

[ApiController]
[Produces("application/json")]
public class SomeController
{
     private async Task<ApiOutput> RunApiForClientAsync(ApiInput input)
    {
        try
        {
            //create a httpclient with a lot of configuration
            var response = await client.SendAsync(request);
            var content = await response.Content.ReadAsStringAsync();

            return new ApiOutput
            {
                Data = content,
                Error = null,
                StatusCode = 200,
                Input = input,
            };
        }
        catch(Exception ex)
        {
            return new ApiOutput
            {
                Data = null,
                Error = new ApiError("Error Getting the Result from the Server", ex.Message),
                StatusCode = 400,
                Input = input,
            };
        }
    }

    private async Task<List<ApiOutput>> RunApiCallsAsync(string requestId, IEnumerable<ApiInput> items)
    {
        var result = new List<ApiOutput>();
        var tasks = new List<Task<ApiOutput>>();

        foreach(var item in items)
        {
            tasks.Add(RunApiForAsync(item));
        }

        var taskResults = await Task.WhenAll(tasks);
        result.AddRange(taskResults);
        return result;
    }

    [HttpPost]
    [Route("rest/multiple")]
    public async Task<IActionResult> PostMultiple(ApiInput[] models, string? requestId)
    {
        _logger.LogInformation(ApiLoggingEvents.PostMultiple, "Request received with ID {requestId}", requestId);
        var result = await RunApiCallsAsync(requestId, models);

        try
        {
            _logger.LogDebug(ApiLoggingEvents.PostMultiple, "Request ID {requestId} Generating JSONs.", requestId);
            
            var resultJson = GetJson(result);
            await SaveResultAsync(resultJson, requestId);

            _logger.LogDebug(ApiLoggingEvents.PostMultiple, "Request ID {requestId} Everything is finished. Returning....", requestId);
            return Content(resultJson, "application/json");
        }
        catch (Exception ex)
        {
            _logger.LogDebug(ApiLoggingEvents.PostMultiple, "Exception while returning {requestId}, message {msg}", requestId, ex.Message);
            throw new Exception("Try again");
        }
    }
}

服务偶发出现调用方发起请求后始终无法收到响应的问题，但查看服务端日志可见对应请求已执行到打印Everything is finished. Returning的步骤，证明业务逻辑全部执行成功；同时await SaveResultAsync(resultJson, requestId);执行正常，结果JSON已保存到服务器本地磁盘。出现该问题的均为长耗时请求，通常响应时长约10分钟。
曾尝试通过如下代码配置Kestrel参数，但该配置对IIS In-Process托管模式不生效：

builder.WebHost.UseKestrel(o =>
{
    o.Limits.MaxConcurrentConnections = 100;
    o.Limits.KeepAliveTimeout = TimeSpan.FromMilliseconds(timeout);
    o.Limits.MaxRequestBodySize = int.MaxValue;
    o.Limits.MaxResponseBufferSize = int.MaxValue;
});

说明：每个请求携带唯一GUID类型的requestId参数，用于日志中追踪请求链路、校验请求执行状态、确认结果文件是否生成。

排查进展 #

• 初步排查发现运行时长超过5分钟的请求均会出现该异常，暂未定位到和5分钟阈值相关的配置项；
• 为复现问题新增了指定延迟时长后返回简单消息的测试接口，代码如下：

[HttpPost]
[Route("rest/testpost")]
public IActionResult TestPost(int delay)
{
    _logger.LogInformation(1, "Delay for {delay} started.", delay);
    Thread.Sleep(delay * 1000);
    _logger.LogInformation(1, "Delay for {delay} ended.", delay);
    return Ok($"Delay for {delay} worked.");
}

• 已在web.config中配置requestTimeout="00:20:00"延长超时时间，但测试发现延迟设置为310秒的请求，依然存在偶发无法返回结果、Postman持续挂起的情况：
  

现咨询该问题的解决方案，确认是否需要调整应用侧或IIS侧的相关配置。

内容的提问来源于stack exchange，提问作者Alireza Noori