How is IIS configured when the server load is high or the request queue is full ??

Question

How is IIS configured when the server load is high or the request queue is full ??

aspx 6

How is IIS configured when the server load is high or the request queue is full and the client requests reject 503 instead of continuing to receive new requests ?

1 . IIS->Application Pools->TestSite->Advanced Settings->Queue Length （default value:65535）
2. IIS->TestSite->Manage Website->Advanced Settings->Limits->Maximum Concurrent Connections （default value:4294967295）

In addition, what other queue configurations can be set? ?

Ask professionals to give pointers，please...

Lex Li (Microsoft) 6,037 Reputation points Microsoft Employee

2022-01-06T17:26:34.957+00:00

https://learn.microsoft.com/en-us/troubleshoot/iis/http-status-code "IIS 7.0 and later versions define the following HTTP status codes that indicate a more specific cause of an error 503" so you should get started from IIS log files and Windows HTTP.sys log files.
Bruce Zhang-MSFT 3,771 Reputation points

2022-01-07T03:07:34.413+00:00

Hi @aspx ,

You need to learn how IIS handle requests first. Introduction to IIS Architectures

Queue Length means requests waiting in the queue. I have explained it in your another question. By the way, it's default value is 1000.
Maximum Concurrent Connections represents that http.sys can pass so many concurrent requests to other modules of IIS and asp.net routing. But the amount of concurrency that an application in a site can actually handle is itself affected. This means that it does not make much sense to increase the concurrent requests of IIS. What should be improved is the application's own thread scheduling, database and disk IO read and write.

If you want to improve the performance to handle concurrent request, what you can set at server level is using ARR with server farm.

5 answers

Your answer

Lex Li (Microsoft) 6,037 Reputation points Microsoft Employee

2022-01-06T17:26:34.957+00:00

https://learn.microsoft.com/en-us/troubleshoot/iis/http-status-code "IIS 7.0 and later versions define the following HTTP status codes that indicate a more specific cause of an error 503" so you should get started from IIS log files and Windows HTTP.sys log files.
Bruce Zhang-MSFT 3,771 Reputation points

2022-01-07T03:07:34.413+00:00

Hi @aspx ,

You need to learn how IIS handle requests first. Introduction to IIS Architectures

Queue Length means requests waiting in the queue. I have explained it in your another question. By the way, it's default value is 1000.
Maximum Concurrent Connections represents that http.sys can pass so many concurrent requests to other modules of IIS and asp.net routing. But the amount of concurrency that an application in a site can actually handle is itself affected. This means that it does not make much sense to increase the concurrent requests of IIS. What should be improved is the application's own thread scheduling, database and disk IO read and write.

If you want to improve the performance to handle concurrent request, what you can set at server level is using ARR with server farm.

Answer 1

aspx 6

@AgaveJoe @Bruce Zhang-MSFT

Answer 2

in general, you would not tweak the IIS settings, but fix the code.

if you have high queue depth, then your code has too many sync operations, too compute bound, or is too slow and needs to be corrected.

to improve performance, you determine what resource is exhausted/slowest first, then improve.

server resources to monitor

1) cpu. once you hit 100%, improve code, or add cpu / servers
2) network. one the network interfaces is maxed, add network interfaces
3) disk maxed, add drives
4) paging high - add memory
5) database - distribute or add caching

Answer 3

thank you..

Microsoft official documentation, the principles and architecture of IIS, is not systematic，scattered，stale, too many configuration, confusingly , is a black box.

IIS->TestSite->Manage Website->Advanced Settings->Limits->Maximum Concurrent Connections （default value:4294967295）
IIS->Application Pools->TestSite->Advanced Settings->Queue Length （default value:65535）IIS http.sys
C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Config\machine.config

<system.web><processModel
enable = "true" [true|false]
requestLimit = "2147483647" [number]
requestQueueLimit = "5000" [number]
memoryLimit = "60" [number]
webGarden = "false" [true|false]
cpuMask = "0xffffffff" [number]
autoConfig = "false" [true|false]
maxWorkerThreads = "20" [number]
maxIoThreads = "20" [number]
minWorkerThreads = "1" [number]
minIoThreads = "1" [number]
maxAppDomains = "2000" [number] .....
/></system.web>
https://learn.microsoft.com/zh-cn/biztalk/technical-guides/optimizing-iis-performance

4.IIS thread pool configuration
HKLM\System\CurrentControlSet\Services\InetInfo\Parameters
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\InetInfo\Parameters\MaxPoolThreads (REG_DWORD)
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\InetInfo\Parameters\PoolThreadLimit (REG_DWORD)
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\InetInfo\Parameters\ThreadTimeout (REG_DWORD)
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\InetInfo\Parameters\ThreadPoolStartupThreadCount (REG_DWORD)
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\InetInfo\Parameters\ThreadPoolMaxCPU (REG_DWORD)
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\InetInfo\Parameters\ThreadPoolStartDelay (REG_DWORD)
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\InetInfo\Parameters\ThreadPoolExactThreadCount (REG_DWORD)
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\InetInfo\Parameters\MaxConcurrency (REG_DWORD)

5.appConcurrentRequestLimit
C:\Windows\System32\inetsrv\config\applicationHost.config
<system.webServer><serverRuntime enable="true" appConcurrentRequestLimit="5000" /> </system.webServer>

ASP.NET 4 MaxConcurrentRequests
<system.web><applicationPool maxConcurrentRequestsPerCPU="5000" maxConcurrentThreadsPerCPU="0" requestQueueLimit="5000" /></system.web>

@Bruce (SqlWork.com)

Answer 4

Bruce (SqlWork.com) 77,686 Volunteer Moderator

IIS is old. Originally windows only supported 256 network connections, and 2gb virtual user memory

A current version of windows has fewer resource limitations and is largely self tuning. So the default iis settings are the max.

Typically iis is not the limiting factor. For .net web sites the ,net 4.* asp.net pipeline design was the main system limitation. If you are using the 4.* framework than this framework is the system limitation. You should start with the defaults. In general increasing thread pool counts reduce performance and only used to fix poorly written code. Adding web gardens may also help with a class of poorly written applications where the requests take too long to process, but not cpu bound.

The .net core pipeline is orders of magnitude improvement in request processing than the old pipeline. So now the code design is truly the limiting factor, not iis or the asp.net processing pipeline.

In short, if you have performance issues, it’s likely your code.

aspx 6 Reputation points

2022-01-10T02:13:22.507+00:00

https://learn.microsoft.com/en-us/dotnet/framework/configure-apps/file-schema/web/applicationpool-element-web-settings?redirectedfrom=MSDN

<applicationPool
maxConcurrentRequestsPerCPU="5000"
maxConcurrentThreadsPerCPU="0"
requestQueueLimit="5000" />

Set this to web.config or machine.config, The result is that the configuration data is invalid or missing a section declaration(iis broken)

ps:
OS: Windows Server 2016 Standard
IIS: Version 10.0.14393.0
Web Sites: WebIISQueueTest .NetFramework4.5 Asp.net mvc
C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Config\machine.config
Bruce Zhang-MSFT 3,771 Reputation points

2022-01-10T06:21:32.89+00:00

Hi @aspx ,

Please read docs more careful.

The applicationPool settings apply to all application pools that run on a particular version of the .NET Framework. The settings are contained in an aspnet.config file. There is a version of this file for versions 2.0 and 4.0 of the .NET Framework. (Versions 3.0 and 3.5 of the .NET Framework share the aspnet.config file with version 2.0.)
aspx 6 Reputation points

2022-01-10T07:49:23.917+00:00

only set this to web.config , The result is that the configuration data is invalid
Bruce Zhang-MSFT 3,771 Reputation points

2022-01-11T02:31:09.463+00:00

Hi @aspx ,

ApplicationPool elements are not set in web.config. The docs has said they are contained in aspnet.config file.

If you have used nginx as load balance, the server with high load should be nginx, not the backend server IIS.

Answer 5

Ken Tucker 5,861

If your web server call not handle all the traffic I would recommend setting up a load balancer so you can spread the traffic over more than one server.

https://learn.microsoft.com/en-us/iis/web-hosting/scenario-build-a-web-farm-with-iis-servers/configuring-step-3-configure-iis-web-farm-load-balancing

aspx 6 Reputation points

2022-01-10T10:50:16.92+00:00

Thank you.
We are using KONG , based on Nginx/OpenResty

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How is IIS configured when the server load is high or the request queue is full ??

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