Multiple ASP.NET Core Web API instances runs only once

Question

Multiple ASP.NET Core Web API instances runs only once

Adriano Iannotta 0

I have an ASP.NET Core 8.0 Web API hosted on two IIS applications (app-1 and app-2) under the Default Web Site on a Windows 11.

Both IIS applications point to the same physical path (inetpub\wwwroot\myapp) and each application has its own dedicated application pool (app1 and app2). The application pools have unique identities (app1svc and app2svc), both of which are members of the Administrators group.

In the Web API, I have an AppEvents class implementing IHostedService, with StartAsync and StopAsync methods to handle application start and stop events. In the Program.cs, I register it using builder.Services.AddHostedService<AppEvents>().

When accessing http://localhost/app-1, the StartAsync method is triggered as expected. However, when accessing http://localhost/app-2, the StartAsync method does not execute. It seems that the application starts only once, despite both IIS apps pointing to the same physical directory.

I've tried changing the AspNetHostingModel from InProcess to OutOfProcess, but the behavior remains the same.

Is there a way to deploy multiple instances of the same web app, each running separately but pointing to the same physical directory, so that each instance correctly triggers its own StartAsync?

Brando Zhang-MSFT 3,956 Reputation points Microsoft External Staff

2024-12-02T11:46:25.9333333+00:00

Hi @Adriano Iannotta, could you please share the event class (AppEvents) and the web.config for this application to let us reproduce the issue?
Adriano Iannotta 0 Reputation points

2024-12-02T16:10:20.7866667+00:00
You can reproduce the problem also monitoring directly the program.cs, without using the AppEvents.cs.

Infact the problem is already evident in it; that is the second request (http://localhost/app-2) does not go through program.cs.

Follows the web.config

<?xml version="1.0" encoding="utf-8"?>

<configuration>

<location path="." inheritInChildApplications="false">

<system.webServer> <handlers> <add name="aspNetCore" path="*" verb="*" modules="AspNetCoreModuleV2" resourceType="Unspecified" /> </handlers> <aspNetCore processPath="dotnet" arguments=".\ZSuite.WebApi.dll" stdoutLogEnabled="false" stdoutLogFile=".\logs\stdout" hostingModel="InProcess" /> </system.webServer>

</location>

</configuration>
Brando Zhang-MSFT 3,956 Reputation points Microsoft External Staff

2024-12-03T07:51:51.08+00:00

In my opinion, this is related with how IIS recognize asp.net core is loaded or not. Since you are using the same directory the same web.config, I suggest you copy it to the different folder and test again.
Adriano Iannotta 0 Reputation points

2024-12-03T08:57:34.8933333+00:00

Hi Brando,

thanks for your reply.

In my previous Web Api developed using .NET Framework this "multi-istance" works properly.

There is only one physical app folder (then only one web.config) and more IIS web application pointing that folder.

The problem is with Web Api developed using .NET Core.

I agree for the relationship between IIS and ASP.NET Core, but is it possible to have the same mechanism (relationship with IIS) of ASP.NET Framework? for example some configuration options...

I don't want to publish more copies (and mantain updated) of the same physical application (it's very expensive)

Can you help me?
Adriano Iannotta 0 Reputation points

2024-12-03T08:58:55.1966667+00:00

Hi Brando,

thanks for your reply.

In my previous Web Api developed using .NET Framework this "multi-istance" works properly.

There is only one physical app folder (then only one web.config) and more IIS web application pointing that folder.

The problem is with Web Api developed using .NET Core.

I agree for the relationship between IIS and ASP.NET Core, but is it possible to have the same mechanism (relationship with IIS) of ASP.NET Framework? for example some configuration options...

I don't want to publish more copies (and mantain updated) of the same physical application (it's very expensive)

Can you help me?
Adriano Iannotta 0 Reputation points

2024-12-03T16:09:19.08+00:00

Hi Brando,

after several hours I've found the "really" problem.

For the monitoring I use NLog (5.2.0); this version of NLog on the second "instance" of WebApi does not write the output.

Thank you very much for your availability
Adriano Iannotta 0 Reputation points

2024-12-03T16:59:21.3333333+00:00

Hi Brando,

after several hours I've found the "real" problerm.

For monitoring I use NLog; the problem is that in the second "instance" of WebApi NLog does not write.

Thank you very much for your availability

Your answer

Brando Zhang-MSFT 3,956 Reputation points Microsoft External Staff

2024-12-02T11:46:25.9333333+00:00

Hi @Adriano Iannotta, could you please share the event class (AppEvents) and the web.config for this application to let us reproduce the issue?
Adriano Iannotta 0 Reputation points

2024-12-02T16:10:20.7866667+00:00

You can reproduce the problem also monitoring directly the program.cs, without using the AppEvents.cs.

Infact the problem is already evident in it; that is the second request (http://localhost/app-2) does not go through program.cs.

Follows the web.config

<?xml version="1.0" encoding="utf-8"?>

<configuration>

<location path="." inheritInChildApplications="false">

<system.webServer> <handlers> <add name="aspNetCore" path="*" verb="*" modules="AspNetCoreModuleV2" resourceType="Unspecified" /> </handlers> <aspNetCore processPath="dotnet" arguments=".\ZSuite.WebApi.dll" stdoutLogEnabled="false" stdoutLogFile=".\logs\stdout" hostingModel="InProcess" /> </system.webServer>

</location>

</configuration>
Brando Zhang-MSFT 3,956 Reputation points Microsoft External Staff

2024-12-03T07:51:51.08+00:00

In my opinion, this is related with how IIS recognize asp.net core is loaded or not. Since you are using the same directory the same web.config, I suggest you copy it to the different folder and test again.
Adriano Iannotta 0 Reputation points

2024-12-03T08:57:34.8933333+00:00

Hi Brando,

thanks for your reply.

In my previous Web Api developed using .NET Framework this "multi-istance" works properly.

There is only one physical app folder (then only one web.config) and more IIS web application pointing that folder.

The problem is with Web Api developed using .NET Core.

I agree for the relationship between IIS and ASP.NET Core, but is it possible to have the same mechanism (relationship with IIS) of ASP.NET Framework? for example some configuration options...

I don't want to publish more copies (and mantain updated) of the same physical application (it's very expensive)

Can you help me?
Adriano Iannotta 0 Reputation points

2024-12-03T08:58:55.1966667+00:00

Hi Brando,

thanks for your reply.

In my previous Web Api developed using .NET Framework this "multi-istance" works properly.

There is only one physical app folder (then only one web.config) and more IIS web application pointing that folder.

The problem is with Web Api developed using .NET Core.

I agree for the relationship between IIS and ASP.NET Core, but is it possible to have the same mechanism (relationship with IIS) of ASP.NET Framework? for example some configuration options...

I don't want to publish more copies (and mantain updated) of the same physical application (it's very expensive)

Can you help me?
Adriano Iannotta 0 Reputation points

2024-12-03T16:09:19.08+00:00

Hi Brando,

after several hours I've found the "really" problem.

For the monitoring I use NLog (5.2.0); this version of NLog on the second "instance" of WebApi does not write the output.

Thank you very much for your availability
Adriano Iannotta 0 Reputation points

2024-12-03T16:59:21.3333333+00:00

Hi Brando,

after several hours I've found the "real" problerm.

For monitoring I use NLog; the problem is that in the second "instance" of WebApi NLog does not write.

Thank you very much for your availability

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Multiple ASP.NET Core Web API instances runs only once

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