--- title: Troubleshoot ASP.NET Core on Azure App Service and IIS author: rick-anderson description: Learn how to diagnose problems with Azure App Service and Internet Information Services (IIS) deployments of ASP.NET Core apps. monikerRange: '>= aspnetcore-2.1' ms.author: riande ms.custom: mvc ms.date: 7/23/2024 uid: test/troubleshoot-azure-iis --- # Troubleshoot ASP.NET Core on Azure App Service and IIS :::moniker range=">= aspnetcore-8.0" This article provides information on common app startup errors and instructions on how to diagnose errors when an app is deployed to Azure App Service or IIS: [App startup errors](#app-startup-errors) Explains common startup HTTP status code scenarios. [Troubleshoot on Azure App Service](#troubleshoot-on-azure-app-service) Provides troubleshooting advice for apps deployed to Azure App Service. [Troubleshoot on IIS](#troubleshoot-on-iis) Provides troubleshooting advice for apps deployed to IIS or running on IIS Express locally. The guidance applies to both Windows Server and Windows desktop deployments. [Clear package caches](#clear-package-caches) Explains what to do when incoherent packages break an app when performing major upgrades or changing package versions. [Additional resources](#additional-resources) Lists additional troubleshooting topics. ## App startup errors In Visual Studio, the ASP.NET Core project default server is Kestrel. Visual studio can be configured to use [IIS Express](/iis/extensions/introduction-to-iis-express/iis-express-overview). A *502.5 - Process Failure* or a *500.30 - Start Failure* that occurs when debugging locally with IIS Express can be diagnosed using the advice in this topic. ### 403.14 Forbidden The app fails to start. The following error is logged: ``` The Web server is configured to not list the contents of this directory. ``` The error is usually caused by a broken deployment on the hosting system, which includes any of the following scenarios: * The app is deployed to the wrong folder on the hosting system. * The deployment process failed to move all of the app's files and folders to the deployment folder on the hosting system. * The *web.config* file is missing from the deployment, or the *web.config* file contents are malformed. Perform the following steps: 1. Delete all of the files and folders from the deployment folder on the hosting system. 1. Redeploy the contents of the app's *publish* folder to the hosting system using your normal method of deployment, such as Visual Studio, PowerShell, or manual deployment: * Confirm that the *web.config* file is present in the deployment and that its contents are correct. * When hosting on Azure App Service, confirm that the app is deployed to the `D:\home\site\wwwroot` folder. * When the app is hosted by IIS, confirm that the app is deployed to the IIS **Physical path** shown in **IIS Manager**'s **Basic Settings**. 1. Confirm that all of the app's files and folders are deployed by comparing the deployment on the hosting system to the contents of the project's *publish* folder. For more information on the layout of a published ASP.NET Core app, see . For more information on the *web.config* file, see . ### 500 Internal Server Error The app starts, but an error prevents the server from fulfilling the request. This error occurs within the app's code during startup or while creating a response. The response may contain no content, or the response may appear as a *500 Internal Server Error* in the browser. The Application Event Log usually states that the app started normally. From the server's perspective, that's correct. The app did start, but it can't generate a valid response. Run the app at a command prompt on the server or enable the ASP.NET Core Module stdout log to troubleshoot the problem. This error also may occur when the .NET Core Hosting Bundle isn't installed or is corrupted. Installing or repairing the installation of the .NET Core Hosting Bundle (for IIS) or Visual Studio (for IIS Express) may fix the problem. ### 500.0 In-Process Handler Load Failure The worker process fails. The app doesn't start. An unknown error occurred loading [ASP.NET Core Module](xref:host-and-deploy/aspnet-core-module) components. Take one of the following actions: * Contact [Microsoft Support](https://support.microsoft.com/oas/default.aspx?prid=15832) (select **Developer Tools** then **ASP.NET Core**). * Ask a question on Stack Overflow. * File an issue on our [GitHub repository](https://github.com/dotnet/AspNetCore). ### 500.30 In-Process Startup Failure The worker process fails. The app doesn't start. The [ASP.NET Core Module](xref:host-and-deploy/aspnet-core-module) attempts to start the .NET Core CLR in-process, but it fails to start. The cause of a process startup failure can usually be determined from entries in the Application Event Log and the ASP.NET Core Module stdout log. Common failure conditions: * The app is misconfigured due to targeting a version of the ASP.NET Core shared framework that isn't present. Check which versions of the ASP.NET Core shared framework are installed on the target machine. * Using Azure Key Vault, lack of permissions to the Key Vault. Check the access policies in the targeted Key Vault to ensure that the correct permissions are granted. ### 500.31 ANCM Failed to Find Native Dependencies The worker process fails. The app doesn't start. The [ASP.NET Core Module](xref:host-and-deploy/aspnet-core-module) attempts to start the .NET Core runtime in-process, but it fails to start. The most common cause of this startup failure is when the `Microsoft.NETCore.App` or `Microsoft.AspNetCore.App` runtime isn't installed. If the app is deployed to target ASP.NET Core 3.0 and that version doesn't exist on the machine, this error occurs. An example error message follows: ``` The specified framework 'Microsoft.NETCore.App', version '3.0.0' was not found. - The following frameworks were found: 2.2.1 at [C:\Program Files\dotnet\x64\shared\Microsoft.NETCore.App] 3.0.0-preview5-27626-15 at [C:\Program Files\dotnet\x64\shared\Microsoft.NETCore.App] 3.0.0-preview6-27713-13 at [C:\Program Files\dotnet\x64\shared\Microsoft.NETCore.App] 3.0.0-preview6-27714-15 at [C:\Program Files\dotnet\x64\shared\Microsoft.NETCore.App] 3.0.0-preview6-27723-08 at [C:\Program Files\dotnet\x64\shared\Microsoft.NETCore.App] ``` The error message lists all the installed .NET Core versions and the version requested by the app. To fix this error, either: * Install the appropriate version of .NET Core on the machine. * Change the app to target a version of .NET Core that's present on the machine. * Publish the app as a [self-contained deployment](/dotnet/core/deploying/#self-contained-deployments-scd). When running in development (the `ASPNETCORE_ENVIRONMENT` environment variable is set to `Development`), the specific error is written to the HTTP response. The cause of a process startup failure is also found in the Application Event Log. ### 500.32 ANCM Failed to Load dll The worker process fails. The app doesn't start. The most common cause for this error is that the app is published for an incompatible processor architecture. If the worker process is running as a 32-bit app and the app was published to target 64-bit, this error occurs. To fix this error, either: * Republish the app for the same processor architecture as the worker process. * Publish the app as a [framework-dependent deployment](/dotnet/core/deploying/#framework-dependent-executables-fde). ### 500.33 ANCM Request Handler Load Failure The worker process fails. The app doesn't start. The app didn't reference the `Microsoft.AspNetCore.App` framework. Only apps targeting the `Microsoft.AspNetCore.App` framework can be hosted by the [ASP.NET Core Module](xref:host-and-deploy/aspnet-core-module). To fix this error, confirm that the app is targeting the `Microsoft.AspNetCore.App` framework. Check the `.runtimeconfig.json` to verify the framework targeted by the app. ### 500.34 ANCM Mixed Hosting Models Not Supported The worker process can't run both an in-process app and an out-of-process app in the same process. To fix this error, run apps in separate IIS application pools. ### 500.35 ANCM Multiple In-Process Applications in same Process The worker process can't run multiple in-process apps in the same process. To fix this error, run apps in separate IIS application pools. ### 500.36 ANCM Out-Of-Process Handler Load Failure The out-of-process request handler, *aspnetcorev2_outofprocess.dll*, isn't next to the *aspnetcorev2.dll* file. This indicates a corrupted installation of the [ASP.NET Core Module](xref:host-and-deploy/aspnet-core-module). To fix this error, repair the installation of the [.NET Core Hosting Bundle](xref:host-and-deploy/iis/index#install-the-net-core-hosting-bundle) (for IIS) or Visual Studio (for IIS Express). ### 500.37 ANCM Failed to Start Within Startup Time Limit ANCM failed to start within the provided startup time limit. By default, the timeout is 120 seconds. This error can occur when starting a large number of apps on the same machine. Check for CPU/Memory usage spikes on the server during startup. You may need to stagger the startup process of multiple apps. ### 500.38 ANCM Application DLL Not Found ANCM failed to locate the application DLL, which should be next to the executable. This error occurs when hosting an app packaged as a [single-file executable](/dotnet/core/whats-new/dotnet-core-3-0#single-file-executables) using the in-process hosting model. The in-process model requires that the ANCM load the .NET Core app into the existing IIS process. This scenario isn't supported by the single-file deployment model. Use **one** of the following approaches in the app's project file to fix this error: 1. Disable single-file publishing by setting the `PublishSingleFile` MSBuild property to `false`. 1. Switch to the out-of-process hosting model by setting the `AspNetCoreHostingModel` MSBuild property to `OutOfProcess`. ### 502.5 Process Failure The worker process fails. The app doesn't start. The [ASP.NET Core Module](xref:host-and-deploy/aspnet-core-module) attempts to start the worker process but it fails to start. The cause of a process startup failure can usually be determined from entries in the Application Event Log and the ASP.NET Core Module stdout log. A common failure condition is the app is misconfigured due to targeting a version of the ASP.NET Core shared framework that isn't present. Check which versions of the ASP.NET Core shared framework are installed on the target machine. The *shared framework* is the set of assemblies (*.dll* files) that are installed on the machine and referenced by a metapackage such as `Microsoft.AspNetCore.App`. The metapackage reference can specify a minimum required version. For more information, see [The shared framework](https://natemcmaster.com/blog/2018/08/29/netcore-primitives-2/). The *502.5 Process Failure* error page is returned when a hosting or app misconfiguration causes the worker process to fail: ### Failed to start application (ErrorCode '0x800700c1') ``` EventID: 1010 Source: IIS AspNetCore Module V2 Failed to start application '/LM/W3SVC/6/ROOT/', ErrorCode '0x800700c1'. ``` The app failed to start because the app's assembly (*.dll*) couldn't be loaded. This error occurs when there's a bitness mismatch between the published app and the w3wp/iisexpress process. Confirm that the app pool's 32-bit setting is correct: 1. Select the app pool in IIS Manager's **Application Pools**. 1. Select **Advanced Settings** under **Edit Application Pool** in the **Actions** panel. 1. Set **Enable 32-Bit Applications**: * If deploying a 32-bit (x86) app, set the value to `True`. * If deploying a 64-bit (x64) app, set the value to `False`. Confirm that there isn't a conflict between a `` MSBuild property in the project file and the published bitness of the app. ### Failed to start application (ErrorCode '0x800701b1') ``` EventID: 1010 Source: IIS AspNetCore Module V2 Failed to start application '/LM/W3SVC/3/ROOT', ErrorCode '0x800701b1'. ``` The app failed to start because a Windows Service failed to load. One common service that needs to be enabled is the "null" service. The following command enables the `null` Windows Service: ```cmd sc.exe start null ``` ### Connection reset If an error occurs after the headers are sent, it's too late for the server to send a **500 Internal Server Error** when an error occurs. This often happens when an error occurs during the serialization of complex objects for a response. This type of error appears as a *connection reset* error on the client. [Application logging](xref:fundamentals/logging/index) can help troubleshoot these types of errors. ### Default startup limits The [ASP.NET Core Module](xref:host-and-deploy/aspnet-core-module) is configured with a default *startupTimeLimit* of 120 seconds. When left at the default value, an app may take up to two minutes to start before the module logs a process failure. For information on configuring the module, see [Attributes of the aspNetCore element](xref:host-and-deploy/aspnet-core-module#attributes-of-the-aspnetcore-element). ## Troubleshoot on Azure App Service [!INCLUDE [Azure App Service Preview Notice](~/includes/azure-apps-preview-notice.md)] ### Azure App Services Log stream The Azure App Services Log streams logging information as it occurs. To view streaming logs: 1. In the Azure portal, open the app in **App Services**. 1. In the left pane, navigate to **Monitoring** > **App Service Logs**. ![App Service Logs](https://user-images.githubusercontent.com/3605364/183573538-80645002-d1c3-4451-9a2f-91ef4de4e248.png) 1. Select **File System** for **Web Server Logging**. Optionally enable **Application logging**. ![enable logging](https://user-images.githubusercontent.com/3605364/183529287-f63d3e1c-ee5b-4ca1-bcb6-a8c29d8b26f5.png) 1. In the left pane, navigate to **Monitoring** > **Log stream**, and then select **Application logs** or **Web Server Logs**. ![Monitoring Log stream](https://user-images.githubusercontent.com/3605364/183561255-91f3d5e1-141b-413b-a403-91e74a770545.png) The following images shows the application logs output: ![app logs](https://user-images.githubusercontent.com/3605364/183528795-532665c0-ce87-4ed3-8e4d-4b374d469c2a.png) Streaming logs have some latency and might not display immediately. ### Application Event Log (Azure App Service) To access the Application Event Log, use the **Diagnose and solve problems** blade in the Azure portal: 1. In the Azure portal, open the app in **App Services**. 1. Select **Diagnose and solve problems**. 1. Select the **Diagnostic Tools** heading. 1. Under **Support Tools**, select the **Application Events** button. 1. Examine the latest error provided by the *IIS AspNetCoreModule* or *IIS AspNetCoreModule V2* entry in the **Source** column. An alternative to using the **Diagnose and solve problems** blade is to examine the Application Event Log file directly using [Kudu](https://github.com/projectkudu/kudu/wiki): 1. Open **Advanced Tools** in the **Development Tools** area. Select the **Go→** button. The Kudu console opens in a new browser tab or window. 1. Using the navigation bar at the top of the page, open **Debug console** and select **CMD**. 1. Open the **LogFiles** folder. 1. Select the pencil icon next to the `eventlog.xml` file. 1. Examine the log. Scroll to the bottom of the log to see the most recent events. ### Run the app in the Kudu console Many startup errors don't produce useful information in the Application Event Log. You can run the app in the [Kudu](https://github.com/projectkudu/kudu/wiki) Remote Execution Console to discover the error: 1. Open **Advanced Tools** in the **Development Tools** area. Select the **Go→** button. The Kudu console opens in a new browser tab or window. 1. Using the navigation bar at the top of the page, open **Debug console** and select **CMD**. #### Test a 32-bit (x86) app **Current release** 1. `cd d:\home\site\wwwroot` 1. Run the app: * If the app is a [framework-dependent deployment](/dotnet/core/deploying/#framework-dependent-deployments-fdd): ```dotnetcli dotnet .\{ASSEMBLY NAME}.dll ``` * If the app is a [self-contained deployment](/dotnet/core/deploying/#self-contained-deployments-scd): ```console {ASSEMBLY NAME}.exe ``` The console output from the app, showing any errors, is piped to the Kudu console. **Framework-dependent deployment running on a preview release** *Requires installing the ASP.NET Core {VERSION} (x86) Runtime site extension.* 1. `cd D:\home\SiteExtensions\AspNetCoreRuntime.{X.Y}.x32` (`{X.Y}` is the runtime version) 1. Run the app: `dotnet \home\site\wwwroot\{ASSEMBLY NAME}.dll` The console output from the app, showing any errors, is piped to the Kudu console. #### Test a 64-bit (x64) app **Current release** * If the app is a 64-bit (x64) [framework-dependent deployment](/dotnet/core/deploying/#framework-dependent-deployments-fdd): 1. `cd D:\Program Files\dotnet` 1. Run the app: `dotnet \home\site\wwwroot\{ASSEMBLY NAME}.dll` * If the app is a [self-contained deployment](/dotnet/core/deploying/#self-contained-deployments-scd): 1. `cd D:\home\site\wwwroot` 1. Run the app: `{ASSEMBLY NAME}.exe` The console output from the app, showing any errors, is piped to the Kudu console. **Framework-dependent deployment running on a preview release** *Requires installing the ASP.NET Core {VERSION} (x64) Runtime site extension.* 1. `cd D:\home\SiteExtensions\AspNetCoreRuntime.{X.Y}.x64` (`{X.Y}` is the runtime version) 1. Run the app: `dotnet \home\site\wwwroot\{ASSEMBLY NAME}.dll` The console output from the app, showing any errors, is piped to the Kudu console. ### ASP.NET Core Module stdout log (Azure App Service) > [!WARNING] > Failure to disable the stdout log can lead to app or server failure. There's no limit on log file size or the number of log files created. Only use stdout logging to troubleshoot app startup problems. > > For general logging in an ASP.NET Core app after startup, use a logging library that limits log file size and rotates logs. For more information, see [third-party logging providers](xref:fundamentals/logging/index#third-party-logging-providers). The ASP.NET Core Module stdout log often records useful error messages not found in the Application Event Log. To enable and view stdout logs: 1. In the Azure Portal, navigate to the web app. 1. In the **App Service** blade, enter **kudu** in the search box. 1. Select **Advanced Tools** > **Go**. 1. Select **Debug console > CMD**. 1. Navigate to *site/wwwroot* 1. Select the pencil icon to edit the *web.config* file. 1. In the `` element, set `stdoutLogEnabled="true"` and select **Save**. Disable stdout logging when troubleshooting is complete by setting `stdoutLogEnabled="false"`. For more information, see . ### ASP.NET Core Module debug log (Azure App Service) The ASP.NET Core Module debug log provides additional, deeper logging from the ASP.NET Core Module. To enable and view stdout logs: 1. To enable the enhanced diagnostic log, perform either of the following: * Follow the instructions in [Enhanced diagnostic logs](xref:host-and-deploy/iis/logging-and-diagnostics#enhanced-diagnostic-logs) to configure the app for an enhanced diagnostic logging. Redeploy the app. * Add the `` shown in [Enhanced diagnostic logs](xref:host-and-deploy/iis/logging-and-diagnostics#enhanced-diagnostic-logs) to the live app's *web.config* file using the Kudu console: 1. Open **Advanced Tools** in the **Development Tools** area. Select the **Go→** button. The Kudu console opens in a new browser tab or window. 1. Using the navigation bar at the top of the page, open **Debug console** and select **CMD**. 1. Open the folders to the path **site** > **wwwroot**. Edit the *web.config* file by selecting the pencil button. Add the `` section as shown in [Enhanced diagnostic logs](xref:host-and-deploy/iis/logging-and-diagnostics#enhanced-diagnostic-logs). Select the **Save** button. 1. Open **Advanced Tools** in the **Development Tools** area. Select the **Go→** button. The Kudu console opens in a new browser tab or window. 1. Using the navigation bar at the top of the page, open **Debug console** and select **CMD**. 1. Open the folders to the path **site** > **wwwroot**. If you didn't supply a path for the *aspnetcore-debug.log* file, the file appears in the list. If you supplied a path, navigate to the location of the log file. 1. Open the log file with the pencil button next to the file name. Disable debug logging when troubleshooting is complete: To disable the enhanced debug log, perform either of the following: * Remove the `` from the *web.config* file locally and redeploy the app. * Use the Kudu console to edit the *web.config* file and remove the `` section. Save the file. For more information, see . > [!WARNING] > Failure to disable the debug log can lead to app or server failure. There's no limit on log file size. Only use debug logging to troubleshoot app startup problems. > > For general logging in an ASP.NET Core app after startup, use a logging library that limits log file size and rotates logs. For more information, see [third-party logging providers](xref:fundamentals/logging/index#third-party-logging-providers). ### Slow or nonresponsive app (Azure App Service) When an app responds slowly or doesn't respond to a request, see [Troubleshoot slow web app performance issues in Azure App Service](/azure/app-service/app-service-web-troubleshoot-performance-degradation). ### Monitoring blades Monitoring blades provide an alternative troubleshooting experience to the methods described earlier in the topic. These blades can be used to diagnose 500-series errors. Confirm that the ASP.NET Core Extensions are installed. If the extensions aren't installed, install them manually: 1. In the **DEVELOPMENT TOOLS** blade section, select the **Extensions** blade. 1. The **ASP.NET Core Extensions** should appear in the list. 1. If the extensions aren't installed, select the **Add** button. 1. Choose the **ASP.NET Core Extensions** from the list. 1. Select **OK** to accept the legal terms. 1. Select **OK** on the **Add extension** blade. 1. An informational pop-up message indicates when the extensions are successfully installed. If stdout logging isn't enabled, follow these steps: 1. In the Azure portal, select the **Advanced Tools** blade in the **DEVELOPMENT TOOLS** area. Select the **Go→** button. The Kudu console opens in a new browser tab or window. 1. Using the navigation bar at the top of the page, open **Debug console** and select **CMD**. 1. Open the folders to the path **site** > **wwwroot** and scroll down to reveal the *web.config* file at the bottom of the list. 1. Click the pencil icon next to the *web.config* file. 1. Set **stdoutLogEnabled** to `true` and change the **stdoutLogFile** path to: `\\?\%home%\LogFiles\stdout`. 1. Select **Save** to save the updated *web.config* file. Proceed to activate diagnostic logging: 1. In the Azure portal, select the **Diagnostics logs** blade. 1. Select the **On** switch for **Application Logging (Filesystem)** and **Detailed error messages**. Select the **Save** button at the top of the blade. 1. To include failed request tracing, also known as Failed Request Event Buffering (FREB) logging, select the **On** switch for **Failed request tracing**. 1. Select the **Log stream** blade, which is listed immediately under the **Diagnostics logs** blade in the portal. 1. Make a request to the app. 1. Within the log stream data, the cause of the error is indicated. Be sure to disable stdout logging when troubleshooting is complete. To view the failed request tracing logs (FREB logs): 1. Navigate to the **Diagnose and solve problems** blade in the Azure portal. 1. Select **Failed Request Tracing Logs** from the **SUPPORT TOOLS** area of the sidebar. See [Failed request traces section of the Enable diagnostics logging for web apps in Azure App Service topic](/azure/app-service/web-sites-enable-diagnostic-log#failed-request-traces) and the [Application performance FAQs for Web Apps in Azure: How do I turn on failed request tracing?](/azure/app-service/app-service-web-availability-performance-application-issues-faq#how-do-i-turn-on-failed-request-tracing) for more information. For more information, see [Enable diagnostics logging for web apps in Azure App Service](/azure/app-service/web-sites-enable-diagnostic-log). > [!WARNING] > Failure to disable the stdout log can lead to app or server failure. There's no limit on log file size or the number of log files created. > > For routine logging in an ASP.NET Core app, use a logging library that limits log file size and rotates logs. For more information, see [third-party logging providers](xref:fundamentals/logging/index#third-party-logging-providers). ## Troubleshoot on IIS ### Application Event Log (IIS) Access the Application Event Log: 1. Open the Start menu, search for *Event Viewer*, and select the **Event Viewer** app. 1. In **Event Viewer**, open the **Windows Logs** node. 1. Select **Application** to open the Application Event Log. 1. Search for errors associated with the failing app. Errors have a value of *IIS AspNetCore Module* or *IIS Express AspNetCore Module* in the *Source* column. ### Run the app at a command prompt Many startup errors don't produce useful information in the Application Event Log. You can find the cause of some errors by running the app at a command prompt on the hosting system. #### Framework-dependent deployment If the app is a [framework-dependent deployment](/dotnet/core/deploying/#framework-dependent-deployments-fdd): 1. At a command prompt, navigate to the deployment folder and run the app by executing the app's assembly with *dotnet.exe*. In the following command, substitute the name of the app's assembly for \: `dotnet .\.dll`. 1. The console output from the app, showing any errors, is written to the console window. 1. If the errors occur when making a request to the app, make a request to the host and port where Kestrel listens. Using the default host and post, make a request to `http://localhost:5000/`. If the app responds normally at the Kestrel endpoint address, the problem is more likely related to the hosting configuration and less likely within the app. #### Self-contained deployment If the app is a [self-contained deployment](/dotnet/core/deploying/#self-contained-deployments-scd): 1. At a command prompt, navigate to the deployment folder and run the app's executable. In the following command, substitute the name of the app's assembly for \: `.exe`. 1. The console output from the app, showing any errors, is written to the console window. 1. If the errors occur when making a request to the app, make a request to the host and port where Kestrel listens. Using the default host and post, make a request to `http://localhost:5000/`. If the app responds normally at the Kestrel endpoint address, the problem is more likely related to the hosting configuration and less likely within the app. ### ASP.NET Core Module stdout log (IIS) To enable and view stdout logs: 1. Navigate to the site's deployment folder on the hosting system. 1. If the *logs* folder isn't present, create the folder. For instructions on how to enable MSBuild to create the *logs* folder in the deployment automatically, see the [Directory structure](xref:host-and-deploy/directory-structure) topic. 1. Edit the *web.config* file. Set **stdoutLogEnabled** to `true` and change the **stdoutLogFile** path to point to the *logs* folder (for example, `.\logs\stdout`). `stdout` in the path is the log file name prefix. A timestamp, process id, and file extension are added automatically when the log is created. Using `stdout` as the file name prefix, a typical log file is named *stdout_20180205184032_5412.log*. 1. Ensure your application pool's identity has write permissions to the *logs* folder. 1. Save the updated *web.config* file. 1. Make a request to the app. 1. Navigate to the *logs* folder. Find and open the most recent stdout log. 1. Study the log for errors. Disable stdout logging when troubleshooting is complete: 1. Edit the *web.config* file. 1. Set **stdoutLogEnabled** to `false`. 1. Save the file. For more information, see . > [!WARNING] > Failure to disable the stdout log can lead to app or server failure. There's no limit on log file size or the number of log files created. > > For routine logging in an ASP.NET Core app, use a logging library that limits log file size and rotates logs. For more information, see [third-party logging providers](xref:fundamentals/logging/index#third-party-logging-providers). ### ASP.NET Core Module debug log (IIS) Add the following handler settings to the app's *web.config* file to enable ASP.NET Core Module debug log: ```xml ``` Confirm that the path specified for the log exists and that the app pool's identity has write permissions to the location. For more information, see . ### Enable the Developer Exception Page The `ASPNETCORE_ENVIRONMENT` [environment variable can be added to web.config](xref:host-and-deploy/aspnet-core-module#setting-environment-variables) to run the app in the Development environment. As long as the environment isn't overridden in app startup by `UseEnvironment` on the host builder, setting the environment variable allows the [Developer Exception Page](xref:fundamentals/error-handling) to appear when the app is run. ```xml ``` Setting the environment variable for `ASPNETCORE_ENVIRONMENT` is only recommended for use on staging and testing servers that aren't exposed to the Internet. Remove the environment variable from the *web.config* file after troubleshooting. For information on setting environment variables in *web.config*, see [environmentVariables child element of aspNetCore](xref:host-and-deploy/aspnet-core-module#setting-environment-variables). ### Obtain data from an app If an app is capable of responding to requests, obtain request, connection, and additional data from the app using terminal inline middleware. For more information and sample code, see . ### Slow or non-responding app (IIS) A *crash dump* is a snapshot of the system's memory and can help determine the cause of an app crash, startup failure, or slow app. #### App crashes or encounters an exception Obtain and analyze a dump from [Windows Error Reporting (WER)](/windows/desktop/wer/windows-error-reporting): 1. Create a folder to hold crash dump files at `c:\dumps`. The app pool must have write access to the folder. 1. Run the [EnableDumps PowerShell script](https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/test/troubleshoot-azure-iis/scripts/EnableDumps.ps1): * If the app uses the [in-process hosting model](xref:host-and-deploy/iis/index#in-process-hosting-model), run the script for *w3wp.exe*: ```console .\EnableDumps w3wp.exe c:\dumps ``` * If the app uses the [out-of-process hosting model](xref:host-and-deploy/iis/index#out-of-process-hosting-model), run the script for *dotnet.exe*: ```console .\EnableDumps dotnet.exe c:\dumps ``` 1. Run the app under the conditions that cause the crash to occur. 1. After the crash has occurred, run the [DisableDumps PowerShell script](https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/test/troubleshoot-azure-iis/scripts/DisableDumps.ps1): * If the app uses the [in-process hosting model](xref:host-and-deploy/iis/index#in-process-hosting-model), run the script for *w3wp.exe*: ```console .\DisableDumps w3wp.exe ``` * If the app uses the [out-of-process hosting model](xref:host-and-deploy/iis/index#out-of-process-hosting-model), run the script for *dotnet.exe*: ```console .\DisableDumps dotnet.exe ``` After an app crashes and dump collection is complete, the app is allowed to terminate normally. The PowerShell script configures WER to collect up to five dumps per app. > [!WARNING] > Crash dumps might take up a large amount of disk space (up to several gigabytes each). #### App doesn't respond, fails during startup, or runs normally When an app stops responding but doesn't crash, fails during startup, or runs normally, see [User-Mode Dump Files: Choosing the Best Tool](/windows-hardware/drivers/debugger/user-mode-dump-files#choosing-the-best-tool) to select an appropriate tool to produce the dump. #### Analyze the dump A dump can be analyzed using several approaches. For more information, see [Analyzing a User-Mode Dump File](/windows-hardware/drivers/debugger/analyzing-a-user-mode-dump-file). ## Clear package caches A functioning app may fail immediately after upgrading either the .NET Core SDK on the development machine or changing package versions within the app. In some cases, incoherent packages may break an app when performing major upgrades. Most of these issues can be fixed by following these instructions: 1. Delete the *bin* and *obj* folders. 1. Clear the package caches by executing [dotnet nuget locals all --clear](/dotnet/core/tools/dotnet-nuget-locals) from a command shell. Clearing package caches can also be accomplished with the [nuget.exe](https://www.nuget.org/downloads) tool and executing the command `nuget locals all -clear`. *nuget.exe* isn't a bundled install with the Windows desktop operating system and must be obtained separately from the [NuGet website](https://www.nuget.org/downloads). 1. Restore and rebuild the project. 1. Delete all of the files in the deployment folder on the server prior to redeploying the app. ## Additional resources * * * * * ### Azure documentation * [Application Insights for ASP.NET Core](/azure/application-insights/app-insights-asp-net-core) * [Remote debugging web apps section of Troubleshoot a web app in Azure App Service using Visual Studio](/azure/app-service/web-sites-dotnet-troubleshoot-visual-studio#remotedebug) * [Azure App Service diagnostics overview](/azure/app-service/app-service-diagnostics) * [How to: Monitor Apps in Azure App Service](/azure/app-service/web-sites-monitor) * [Troubleshoot a web app in Azure App Service using Visual Studio](/azure/app-service/web-sites-dotnet-troubleshoot-visual-studio) * [Troubleshoot HTTP errors of "502 bad gateway" and "503 service unavailable" in your Azure web apps](/azure/app-service/app-service-web-troubleshoot-http-502-http-503) * [Troubleshoot slow web app performance issues in Azure App Service](/azure/app-service/app-service-web-troubleshoot-performance-degradation) * [Application performance FAQs for Web Apps in Azure](/azure/app-service/app-service-web-availability-performance-application-issues-faq) * [Azure Web App sandbox (App Service runtime execution limitations)](https://github.com/projectkudu/kudu/wiki/Azure-Web-App-sandbox) ### Visual Studio documentation * [Remote Debug ASP.NET Core on IIS in Azure in Visual Studio 2017](/visualstudio/debugger/remote-debugging-azure) * [Remote Debug ASP.NET Core on a Remote IIS Computer in Visual Studio 2017](/visualstudio/debugger/remote-debugging-aspnet-on-a-remote-iis-computer) * [Learn to debug using Visual Studio](/visualstudio/debugger/getting-started-with-the-debugger) ### Visual Studio Code documentation * [Debugging with Visual Studio Code](https://code.visualstudio.com/docs/editor/debugging) :::moniker-end [!INCLUDE[](~/test/troubleshoot-azure-iis/includes/troubleshoot-azure-iis2.md)] [!INCLUDE[](~/test/troubleshoot-azure-iis/includes/troubleshoot-azure-iis7.md)]