This topic describes the most common errors and provides troubleshooting advice when hosting ASP.NET Core apps on Azure Apps Service and IIS.
See <xref:test/troubleshoot-azure-iis> information on common app startup errors and instructions on how to diagnose errors.
Collect the following information:
* Browser behavior such as status code and error message.
* Application Event Log entries
* Azure App Service: See <xref:test/troubleshoot-azure-iis>.
* IIS
1. Select **Start** on the **Windows** menu, type *Event Viewer*, and press **Enter**.
1. After the **Event Viewer** opens, expand **Windows Logs** > **Application** in the sidebar.
* ASP.NET Core Module stdout and debug log entries
* Azure App Service: See <xref:test/troubleshoot-azure-iis>.
* IIS: Follow the instructions in the [Log creation and redirection](xref:host-and-deploy/aspnet-core-module#log-creation-and-redirection) and [Enhanced diagnostic logs](xref:host-and-deploy/iis/logging-and-diagnostics#enhanced-diagnostic-logs) sections of the ASP.NET Core Module topic.
Compare error information to the following common errors. If a match is found, follow the troubleshooting advice.
The list of errors in this topic isn't exhaustive. If you encounter an error not listed here, open a new issue using the **Content feedback** button at the bottom of this topic with detailed instructions on how to reproduce the error.
## OS upgrade removed the 32-bit ASP.NET Core Module
**Application Log:** The Module DLL **C:\WINDOWS\system32\inetsrv\aspnetcore.dll** failed to load. The data is the error.
Troubleshooting:
Non-OS files in the **C:\Windows\SysWOW64\inetsrv** directory aren't preserved during an OS upgrade. If the ASP.NET Core Module is installed prior to an OS upgrade and then any app pool is run in 32-bit mode after an OS upgrade, this issue is encountered. After an OS upgrade, repair the ASP.NET Core Module. See [Install the .NET Core Hosting bundle](xref:host-and-deploy/iis/index#install-the-net-core-hosting-bundle). Select **Repair** when the installer is run.
## Missing site extension, 32-bit (x86) and 64-bit (x64) site extensions installed, or wrong process bitness set
* **Application Log:** Invoking hostfxr to find the inprocess request handler failed without finding any native dependencies. Could not find inprocess request handler. Captured output from invoking hostfxr: It was not possible to find any compatible framework version. The specified framework 'Microsoft.AspNetCore.App', version '{VERSION}-preview-\*' was not found. Failed to start application '/LM/W3SVC/1416782824/ROOT', ErrorCode '0x8000ffff'.
* **ASP.NET Core Module stdout Log:** It was not possible to find any compatible framework version. The specified framework 'Microsoft.AspNetCore.App', version '{VERSION}-preview-\*' was not found.
* **ASP.NET Core Module Debug Log:** Invoking hostfxr to find the inprocess request handler failed without finding any native dependencies. This most likely means the app is misconfigured, please check the versions of Microsoft.NetCore.App and Microsoft.AspNetCore.App that are targeted by the application and are installed on the machine. Failed HRESULT returned: 0x8000ffff. Could not find inprocess request handler. It was not possible to find any compatible framework version. The specified framework 'Microsoft.AspNetCore.App', version '{VERSION}-preview-\*' was not found.
Troubleshooting:
* If running the app on a preview runtime, install either the 32-bit (x86) **or** 64-bit (x64) site extension that matches the bitness of the app and the app's runtime version. **Don't install both extensions or multiple runtime versions of the extension.**
* ASP.NET Core {RUNTIME VERSION} (x86) Runtime
* ASP.NET Core {RUNTIME VERSION} (x64) Runtime
Restart the app. Wait several seconds for the app to restart.
* If running the app on a preview runtime and both the 32-bit (x86) and 64-bit (x64) [site extensions](xref:host-and-deploy/azure-apps/index#install-the-preview-site-extension) are installed, uninstall the site extension that doesn't match the bitness of the app. After removing the site extension, restart the app. Wait several seconds for the app to restart.
* If running the app on a preview runtime and the site extension's bitness matches that of the app, confirm that the preview site extension's *runtime version* matches the app's runtime version.
* Confirm that the app's **Platform** in **Application Settings** matches the bitness of the app.
For more information, see <xref:host-and-deploy/azure-apps/index#install-the-preview-site-extension>.
## An x86 app is deployed but the app pool isn't enabled for 32-bit apps
This scenario is trapped by the SDK when publishing a self-contained app. The SDK produces an error if the RID doesn't match the platform target (for example, `win10-x64` RID with `<PlatformTarget>x86</PlatformTarget>` in the project file).
Troubleshooting:
For an x86 framework-dependent deployment (`<PlatformTarget>x86</PlatformTarget>`), enable the IIS app pool for 32-bit apps. In IIS Manager, open the app pool's **Advanced Settings** and set **Enable 32-Bit Applications** to **True**.
## Platform conflicts with RID
* **Browser:** HTTP Error 502.5 - Process Failure
* **Application Log:** Application 'MACHINE/WEBROOT/APPHOST/{ASSEMBLY}' with physical root 'C:\{PATH}\' failed to start process with commandline '"C:\{PATH}{ASSEMBLY}.{exe|dll}" ', ErrorCode = '0x80004005 : ff.
* **ASP.NET Core Module stdout Log:** Unhandled Exception: System.BadImageFormatException: Could not load file or assembly '{ASSEMBLY}.dll'. An attempt was made to load a program with an incorrect format.
Troubleshooting:
* Confirm that the app runs locally on Kestrel. A process failure might be the result of a problem within the app. For more information, see <xref:test/troubleshoot-azure-iis>.
* If this exception occurs for an Azure Apps deployment when upgrading an app and deploying newer assemblies, manually delete all files from the prior deployment. Lingering incompatible assemblies can result in a `System.BadImageFormatException` exception when deploying an upgraded app.
## URI endpoint wrong or stopped website
* **Browser:** ERR_CONNECTION_REFUSED **--OR--** Unable to connect
Check the IIS website **Basic Settings** and the physical app folder. Confirm that the app is in the folder at the IIS website **Physical path**.
## Incorrect role, ASP.NET Core Module not installed, or incorrect permissions
* **Browser:** 500.19 Internal Server Error - The requested page cannot be accessed because the related configuration data for the page is invalid. **--OR--** This page can't be displayed
* Confirm that the proper role is enabled. See [IIS Configuration](xref:host-and-deploy/iis/index#iis-configuration).
* Open **Programs & Features** or **Apps & features** and confirm that **Windows Server Hosting** is installed. If **Windows Server Hosting** isn't present in the list of installed programs, download and install the .NET Core Hosting Bundle.
For more information, see [Install the .NET Core Hosting Bundle](xref:host-and-deploy/iis/index#install-the-net-core-hosting-bundle).
* Make sure that the **Application Pool** > **Process Model** > **Identity** is set to **ApplicationPoolIdentity** or the custom identity has the correct permissions to access the app's deployment folder.
* If you uninstalled the ASP.NET Core Hosting Bundle and installed an earlier version of the hosting bundle, the *applicationHost.config* file doesn't include a section for the ASP.NET Core Module. Open *applicationHost.config* at *%windir%/System32/inetsrv/config* and find the `<configuration><configSections><sectionGroup name="system.webServer">` section group. If the section for the ASP.NET Core Module is missing from the section group, add the section element:
Alternatively, install the latest version of the ASP.NET Core Hosting Bundle. The latest version is backwards-compatible with supported ASP.NET Core apps.
## Incorrect processPath, missing PATH variable, Hosting Bundle not installed, system/IIS not restarted, VC++ Redistributable not installed, or dotnet.exe access violation
* **Application Log:** Application 'MACHINE/WEBROOT/APPHOST/{ASSEMBLY}' with physical root 'C:\{PATH}\' failed to start process with commandline '"{...}" ', ErrorCode = '0x80070002 : 0. Application '{PATH}' wasn't able to start. Executable was not found at '{PATH}'. Failed to start application '/LM/W3SVC/2/ROOT', ErrorCode '0x8007023e'.
* **ASP.NET Core Module Debug Log:** Event Log: 'Application '{PATH}' wasn't able to start. Executable was not found at '{PATH}'. Failed HRESULT returned: 0x8007023e
Troubleshooting:
* Confirm that the app runs locally on Kestrel. A process failure might be the result of a problem within the app. For more information, see <xref:test/troubleshoot-azure-iis>.
* Check the *processPath* attribute on the `<aspNetCore>` element in *web.config* to confirm that it's `dotnet` for a framework-dependent deployment (FDD) or `.\{ASSEMBLY}.exe` for a [self-contained deployment (SCD)](/dotnet/core/deploying/#self-contained-deployments-scd).
* For an FDD, *dotnet.exe* might not be accessible via the PATH settings. Confirm that *C:\Program Files\dotnet\\* exists in the System PATH settings.
* For an FDD, *dotnet.exe* might not be accessible for the user identity of the app pool. Confirm that the app pool user identity has access to the *C:\Program Files\dotnet* directory. Confirm that there are no deny rules configured for the app pool user identity on the *C:\Program Files\dotnet* and app directories.
* An FDD may have been deployed and .NET Core installed without restarting IIS. Either restart the server or restart IIS by executing **net stop was /y** followed by **net start w3svc** from a command prompt.
* An FDD may have been deployed without installing the .NET Core runtime on the hosting system. If the .NET Core runtime hasn't been installed, run the **.NET Core Hosting Bundle installer** on the system.
For more information, see [Install the .NET Core Hosting Bundle](xref:host-and-deploy/iis/index#install-the-net-core-hosting-bundle).
If a specific runtime is required, download the runtime from the [.NET Downloads](https://dotnet.microsoft.com/download/dotnet) page and install it on the system. Complete the installation by restarting the system or restarting IIS by executing **net stop was /y** followed by **net start w3svc** from a command prompt.
* **Application Log:** Invoking hostfxr to find the inprocess request handler failed without finding any native dependencies. This most likely means the app is misconfigured, please check the versions of Microsoft.NetCore.App and Microsoft.AspNetCore.App that are targeted by the application and are installed on the machine. Could not find inprocess request handler. Captured output from invoking hostfxr: Did you mean to run dotnet SDK commands? Please install dotnet SDK from: https://go.microsoft.com/fwlink/?LinkID=798306&clcid=0x409 Failed to start application '/LM/W3SVC/3/ROOT', ErrorCode '0x8000ffff'.
* **ASP.NET Core Module stdout Log:** Did you mean to run dotnet SDK commands? Please install dotnet SDK from: https://go.microsoft.com/fwlink/?LinkID=798306&clcid=0x409
* **ASP.NET Core Module Debug Log:** Invoking hostfxr to find the inprocess request handler failed without finding any native dependencies. This most likely means the app is misconfigured, please check the versions of Microsoft.NetCore.App and Microsoft.AspNetCore.App that are targeted by the application and are installed on the machine. Failed HRESULT returned: 0x8000ffff Could not find inprocess request handler. Captured output from invoking hostfxr: Did you mean to run dotnet SDK commands? Please install dotnet SDK from: https://go.microsoft.com/fwlink/?LinkID=798306&clcid=0x409 Failed HRESULT returned: 0x8000ffff
Troubleshooting:
* Confirm that the app runs locally on Kestrel. A process failure might be the result of a problem within the app. For more information, see <xref:test/troubleshoot-azure-iis>.
* Examine the *arguments* attribute on the `<aspNetCore>` element in *web.config* to confirm that it's either (a) `.\{ASSEMBLY}.dll` for a framework-dependent deployment (FDD); or (b) not present, an empty string (`arguments=""`), or a list of the app's arguments (`arguments="{ARGUMENT_1}, {ARGUMENT_2}, ... {ARGUMENT_X}"`) for a self-contained deployment (SCD).
* **Application Log:** Invoking hostfxr to find the inprocess request handler failed without finding any native dependencies. This most likely means the app is misconfigured, please check the versions of Microsoft.NetCore.App and Microsoft.AspNetCore.App that are targeted by the application and are installed on the machine. Could not find inprocess request handler. Captured output from invoking hostfxr: It was not possible to find any compatible framework version. The specified framework 'Microsoft.AspNetCore.App', version '{VERSION}' was not found.
Failed to start application '/LM/W3SVC/5/ROOT', ErrorCode '0x8000ffff'.
* **ASP.NET Core Module stdout Log:** It was not possible to find any compatible framework version. The specified framework 'Microsoft.AspNetCore.App', version '{VERSION}' was not found.
Confirm that the Application Pool isn't in the *Stopped* state.
## Sub-application includes a \<handlers> section
* **Browser:** HTTP Error 500.19 - Internal Server Error
* **Application Log:** No entry
* **ASP.NET Core Module stdout Log:** The root app's log file is created and shows normal operation. The sub-app's log file isn't created.
* **ASP.NET Core Module Debug Log:** The root app's log file is created and shows normal operation. The sub-app's log file isn't created.
Troubleshooting:
Confirm that the sub-app's *web.config* file doesn't include a `<handlers>` section or that the sub-app doesn't inherit the parent app's handlers.
The parent app's `<system.webServer>` section of *web.config* is placed inside of a `<location>` element. The <xref:System.Configuration.SectionInformation.InheritInChildApplications*> property is set to `false` to indicate that the settings specified within the [\<location>](/iis/manage/managing-your-configuration-settings/understanding-iis-configuration-delegation#the-concept-of-location) element aren't inherited by apps that reside in a subdirectory of the parent app. For more information, see <xref:host-and-deploy/aspnet-core-module>.
## stdout log path incorrect
* **Browser:** The app responds normally.
* **Application Log:** Could not start stdout redirection in C:\Program Files\IIS\Asp.Net Core Module\V2\aspnetcorev2.dll. Exception message: HRESULT 0x80070005 returned at {PATH}\aspnetcoremodulev2\commonlib\fileoutputmanager.cpp:84. Could not stop stdout redirection in C:\Program Files\IIS\Asp.Net Core Module\V2\aspnetcorev2.dll. Exception message: HRESULT 0x80070002 returned at {PATH}. Could not start stdout redirection in {PATH}\aspnetcorev2_inprocess.dll.
* **ASP.NET Core Module debug Log:** Could not start stdout redirection in C:\Program Files\IIS\Asp.Net Core Module\V2\aspnetcorev2.dll. Exception message: HRESULT 0x80070005 returned at {PATH}\aspnetcoremodulev2\commonlib\fileoutputmanager.cpp:84. Could not stop stdout redirection in C:\Program Files\IIS\Asp.Net Core Module\V2\aspnetcorev2.dll. Exception message: HRESULT 0x80070002 returned at {PATH}. Could not start stdout redirection in {PATH}\aspnetcorev2_inprocess.dll.
Troubleshooting:
* The `stdoutLogFile` path specified in the `<aspNetCore>` element of *web.config* doesn't exist. For more information, see [ASP.NET Core Module: Log creation and redirection](xref:host-and-deploy/aspnet-core-module#log-creation-and-redirection).
* The app pool user doesn't have write access to the stdout log path.
