Application monitoring for Azure App Service and ASP.NET

Enabling monitoring on your ASP.NET-based web applications running on Azure App Service is now easier than ever. Previously, you needed to manually instrument your app. Now the latest extension/agent is built into the App Service image by default. This article will walk you through enabling Azure Monitor Application Insights monitoring and provide preliminary guidance for automating the process for large-scale deployments.


Manually adding an Application Insights site extension via Development Tools > Extensions is deprecated. This method of extension installation was dependent on manual updates for each new version. The latest stable release of the extension is now preinstalled as part of the App Service image. The files are located in d:\Program Files (x86)\SiteExtensions\ApplicationInsightsAgent and are automatically updated with each stable release. If you follow the autoinstrumentation instructions to enable monitoring, it will automatically remove the deprecated extension for you.

If both autoinstrumentation monitoring and manual SDK-based instrumentation are detected, only the manual instrumentation settings will be honored. This arrangement prevents duplicate data from being sent. To learn more, see the Troubleshooting section.


On March 31, 2025, support for instrumentation key ingestion will end. Instrumentation key ingestion will continue to work, but we'll no longer provide updates or support for the feature. Transition to connection strings to take advantage of new capabilities.

Enable autoinstrumentation monitoring

For a complete list of supported autoinstrumentation scenarios, see Supported environments, languages, and resource providers.


The combination of APPINSIGHTS_JAVASCRIPT_ENABLED and urlCompression isn't supported. For more information, see the explanation in the Troubleshooting section.

  1. Select Application Insights in the Azure control panel for your app service. Then select Enable.

    Screenshot that shows the Application Insights tab with Enable selected.

  2. Choose to create a new resource, or select an existing Application Insights resource for this application.


    When you select OK to create the new resource, you're prompted to select Apply monitoring settings. Selecting Continue links your new Application Insights resource to your app service. Doing so also triggers a restart of your app service.

    Screenshot that shows the Change your resource dropdown.

  3. After you specify which resource to use, you can choose how you want Application Insights to collect data per platform for your application. ASP.NET app monitoring is on by default with two different levels of collection.

    Screenshot that shows the Application Insights site extensions page with Create new resource selected.

    The following table summarizes the data that's collected for each route.

    Data ASP.NET basic collection ASP.NET recommended collection
    Adds CPU, memory, and I/O usage trends No Yes
    Collects usage trends, and enables correlation from availability results to transactions Yes Yes
    Collects exceptions unhandled by the host process Yes Yes
    Improves APM metrics accuracy under load, when sampling is used Yes Yes
    Correlates micro-services across request/dependency boundaries No (single-instance APM capabilities only) Yes
  4. To configure sampling, which you could previously control via the applicationinsights.config file, you can now interact with it via application settings with the corresponding prefix MicrosoftAppInsights_AdaptiveSamplingTelemetryProcessor.

    • For example, to change the initial sampling percentage, you can create an application setting of MicrosoftAppInsights_AdaptiveSamplingTelemetryProcessor_InitialSamplingPercentage and a value of 100.

    • To disable sampling, set MicrosoftAppInsights_AdaptiveSamplingTelemetryProcessor_MinSamplingPercentage to a value of 100.

    • Supported settings include:

      • MicrosoftAppInsights_AdaptiveSamplingTelemetryProcessor_InitialSamplingPercentage
      • MicrosoftAppInsights_AdaptiveSamplingTelemetryProcessor_MinSamplingPercentage
      • MicrosoftAppInsights_AdaptiveSamplingTelemetryProcessor_EvaluationInterval
      • MicrosoftAppInsights_AdaptiveSamplingTelemetryProcessor_MaxTelemetryItemsPerSecond
    • For the list of supported adaptive sampling telemetry processor settings and definitions, see the code and sampling documentation.

Enable client-side monitoring

Client-side monitoring is an opt-in for ASP.NET. To enable client-side monitoring:

  1. Select Settings > Configuration.

  2. Under Application settings, create a new application setting:

    • Value: Enter true.
  3. Save the settings and restart your app.

To disable client-side monitoring, either remove the associated key value pair from Application settings or set the value to false.

Automate monitoring

To enable telemetry collection with Application Insights, only application settings need to be set.

Screenshot that shows App Service application settings with Application Insights settings.

Application settings definitions

App setting name Definition Value
ApplicationInsightsAgent_EXTENSION_VERSION Main extension, which controls runtime monitoring. ~2
XDT_MicrosoftApplicationInsights_Mode In default mode, only essential features are enabled to ensure optimal performance. default or recommended
InstrumentationEngine_EXTENSION_VERSION Controls if the binary-rewrite engine InstrumentationEngine will be turned on. This setting has performance implications and affects cold start/startup time. ~1
XDT_MicrosoftApplicationInsights_BaseExtensions Controls if SQL and Azure table text will be captured along with the dependency calls. Performance warning: Application cold startup time will be affected. This setting requires the InstrumentationEngine. ~1

App Service application settings with Azure Resource Manager

Application settings for Azure App Service can be managed and configured with Azure Resource Manager templates. You can use this method when you deploy new App Service resources with Resource Manager automation or modify the settings of existing resources.

The basic structure of the application settings JSON for an App Service resource:

      "resources": [
          "name": "appsettings",
          "type": "config",
          "apiVersion": "2015-08-01",
          "dependsOn": [
            "[resourceId('Microsoft.Web/sites', variables('webSiteName'))]"
          "tags": {
            "displayName": "Application Insights Settings"
          "properties": {
            "key1": "value1",
            "key2": "value2"

For an example of a Resource Manager template with application settings configured for Application Insights, this template can be helpful. Specifically, see the section that starts on line 238.

To create a Resource Manager template with the default Application Insights settings, begin the process as if you were going to create a new web app with Application Insights enabled.

  1. Create a new App Service resource with your desired web app information. Enable Application Insights on the Monitoring tab.

  2. Select Review + create. Then select Download a template for automation.

    Screenshot that shows the App Service web app creation menu.

    This option generates the latest Resource Manager template with all required settings configured.

    Screenshot that shows an App Service web app template.

In the following sample, replace all instances of AppMonitoredSite with your site name:


If using Windows, set ApplicationInsightsAgent_EXTENSION_VERSION to ~2. If using Linux, set ApplicationInsightsAgent_EXTENSION_VERSION to ~3.

    "resources": [
            "name": "[parameters('name')]",
            "type": "Microsoft.Web/sites",
            "properties": {
                "siteConfig": {
                    "appSettings": [
                            "name": "APPINSIGHTS_INSTRUMENTATIONKEY",
                            "value": "[reference('microsoft.insights/components/AppMonitoredSite', '2015-05-01').InstrumentationKey]"
                            "name": "APPLICATIONINSIGHTS_CONNECTION_STRING",
                            "value": "[reference('microsoft.insights/components/AppMonitoredSite', '2015-05-01').ConnectionString]"
                            "name": "ApplicationInsightsAgent_EXTENSION_VERSION",
                            "value": "~2"
                "name": "[parameters('name')]",
                "serverFarmId": "[concat('/subscriptions/', parameters('subscriptionId'),'/resourcegroups/', parameters('serverFarmResourceGroup'), '/providers/Microsoft.Web/serverfarms/', parameters('hostingPlanName'))]",
                "hostingEnvironment": "[parameters('hostingEnvironment')]"
            "dependsOn": [
                "[concat('Microsoft.Web/serverfarms/', parameters('hostingPlanName'))]",
            "apiVersion": "2016-03-01",
            "location": "[parameters('location')]"
            "apiVersion": "2016-09-01",
            "name": "[parameters('hostingPlanName')]",
            "type": "Microsoft.Web/serverfarms",
            "location": "[parameters('location')]",
            "properties": {
                "name": "[parameters('hostingPlanName')]",
                "workerSizeId": "[parameters('workerSize')]",
                "numberOfWorkers": "1",
                "hostingEnvironment": "[parameters('hostingEnvironment')]"
            "sku": {
                "Tier": "[parameters('sku')]",
                "Name": "[parameters('skuCode')]"
            "apiVersion": "2015-05-01",
            "name": "AppMonitoredSite",
            "type": "microsoft.insights/components",
            "location": "West US 2",
            "properties": {
                "ApplicationId": "[parameters('name')]",
                "Request_Source": "IbizaWebAppExtensionCreate"
    "parameters": {
        "name": {
            "type": "string"
        "hostingPlanName": {
            "type": "string"
        "hostingEnvironment": {
            "type": "string"
        "location": {
            "type": "string"
        "sku": {
            "type": "string"
        "skuCode": {
            "type": "string"
        "workerSize": {
            "type": "string"
        "serverFarmResourceGroup": {
            "type": "string"
        "subscriptionId": {
            "type": "string"
    "$schema": "",
    "contentVersion": ""

Enable through PowerShell

To enable the application monitoring through PowerShell, only the underlying application settings must be changed. The following sample enables application monitoring for a website called AppMonitoredSite in the resource group AppMonitoredRG. It configures data to be sent to the 012345678-abcd-ef01-2345-6789abcd instrumentation key.


We recommend that you use the Azure Az PowerShell module to interact with Azure. To get started, see Install Azure PowerShell. To learn how to migrate to the Az PowerShell module, see Migrate Azure PowerShell from AzureRM to Az.


If using Windows, set ApplicationInsightsAgent_EXTENSION_VERSION to ~2. If using Linux, set ApplicationInsightsAgent_EXTENSION_VERSION to ~3.

$app = Get-AzWebApp -ResourceGroupName "AppMonitoredRG" -Name "AppMonitoredSite" -ErrorAction Stop
$newAppSettings = @{} # case-insensitive hash map
$app.SiteConfig.AppSettings | %{$newAppSettings[$_.Name] = $_.Value} # preserve non Application Insights application settings.
$newAppSettings["APPINSIGHTS_INSTRUMENTATIONKEY"] = "012345678-abcd-ef01-2345-6789abcd"; # set the Application Insights instrumentation key
$newAppSettings["APPLICATIONINSIGHTS_CONNECTION_STRING"] = "InstrumentationKey=012345678-abcd-ef01-2345-6789abcd"; # set the Application Insights connection string
$newAppSettings["ApplicationInsightsAgent_EXTENSION_VERSION"] = "~2"; # enable the ApplicationInsightsAgent
$app = Set-AzWebApp -AppSettings $newAppSettings -ResourceGroupName $app.ResourceGroup -Name $app.Name -ErrorAction Stop

Upgrade monitoring extension/agent: .NET

Upgrade from versions 2.8.9 and up

Upgrading from version 2.8.9 happens automatically, without any extra actions. The new monitoring bits are delivered in the background to the target app service. They'll be picked when the application restarts.

To check which version of the extension you're running, go to

Screenshot that shows the URL path to check the version of the extension you're running.

Upgrade from versions 1.0.0 - 2.6.5

Starting with version 2.8.9, the preinstalled site extension is used. If you're on an earlier version, you can update via one of two ways:

  • Upgrade by enabling via the portal: Even if you have the Application Insights extension for App Service installed. The UI shows only the Enable button. Behind the scenes, the old private site extension will be removed.

  • Upgrade through PowerShell:

    1. Set the application settings to enable the preinstalled site extension ApplicationInsightsAgent. For more information, see Enable through PowerShell.
    2. Manually remove the private site extension named Application Insights extension for App Service.

If the upgrade is done from a version prior to 2.5.1, check that the Application Insights DLLs are removed from the application bin folder. For more information, see the steps in the Troubleshooting section.



When you create a web app with the ASP.NET runtimes in App Service, it deploys a single static HTML page as a starter website. We do not recommend that you troubleshoot an issue with a default template. Deploy an application before you troubleshoot an issue.

Here's our step-by-step troubleshooting guide for extension/agent-based monitoring for ASP.NET-based applications running on App Service.

  1. Check that the ApplicationInsightsAgent_EXTENSION_VERSION app setting is set to a value of ~2.

  2. Browse to

    Screenshot that shows the preceding link's results page.

    • Confirm that Application Insights Extension Status is Pre-Installed Site Extension, version 2.8.x.xxxx and is running.

      If it isn't running, follow the instructions to enable Application Insights monitoring.

    • Confirm that the status source exists and looks like Status source D:\home\LogFiles\ApplicationInsights\status\status_RD0003FF0317B6_4248_1.json.

      If a similar value isn't present, it means the application isn't currently running or isn't supported. To ensure that the application is running, try manually visiting the application URL/application endpoints, which will allow the runtime information to become available.

    • Confirm that IKeyExists is true. If not, add APPINSIGHTS_INSTRUMENTATIONKEY and APPLICATIONINSIGHTS_CONNECTION_STRING with your instrumentation key GUID to your application settings.

    • Confirm that there are no entries for AppAlreadyInstrumented, AppContainsDiagnosticSourceAssembly, and AppContainsAspNetTelemetryCorrelationAssembly.

      If any of these entries exist, remove the following packages from your application: Microsoft.ApplicationInsights, System.Diagnostics.DiagnosticSource, and Microsoft.AspNet.TelemetryCorrelation.

Default website deployed with web apps doesn't support automatic client-side monitoring

When you create a web app with the ASP.NET runtimes in App Service, it deploys a single static HTML page as a starter website. The static webpage also loads an ASP.NET-managed web part in IIS. This page allows for testing codeless server-side monitoring but doesn't support automatic client-side monitoring.

If you want to test out codeless server and client-side monitoring for ASP.NET in an App Service web app, we recommend that you follow the official guides for creating an ASP.NET Framework web app. Then use the instructions in the current article to enable monitoring.

APPINSIGHTS_JAVASCRIPT_ENABLED and urlCompression isn't supported

If you use APPINSIGHTS_JAVASCRIPT_ENABLED=true in cases where content is encoded, you might get errors like:

  • 500 URL rewrite error.
  • 500.53 URL rewrite module error with the message "Outbound rewrite rules can't be applied when the content of the HTTP response is encoded ('gzip')."

An error occurs because the APPINSIGHTS_JAVASCRIPT_ENABLED application setting is set to true and content encoding is present at the same time. This scenario isn't supported yet. The workaround is to remove APPINSIGHTS_JAVASCRIPT_ENABLED from your application settings. Unfortunately, if client/browser-side JavaScript instrumentation is still required, manual SDK references are needed for your webpages. Follow the instructions for manual instrumentation with the JavaScript SDK.

For the latest information on the Application Insights agent/extension, see the release notes.

What's the difference between standard metrics from Application Insights vs. Azure App Service metrics?

Application Insights collects telemetry for the requests that made it to the application. If the failure occurs in WebApps/WebServer, and the request didn't reach the user application, Application Insights doesn't have any telemetry about it.

The duration for serverresponsetime calculated by Application Insights doesn't necessarily match the server response time observed by Web Apps. This behavior is because Application Insights only counts the duration when the request actually reaches the user application. If the request is stuck or queued in WebServer, the waiting time is included in the Web Apps metrics but not in Application Insights metrics.

Test connectivity between your application host and the ingestion service

Application Insights SDKs and agents send telemetry to get ingested as REST calls to our ingestion endpoints. You can test connectivity from your web server or application host machine to the ingestion service endpoints by using raw REST clients from PowerShell or curl commands. See Troubleshoot missing application telemetry in Azure Monitor Application Insights.

PHP and WordPress aren't supported

PHP and WordPress sites aren't supported. There's currently no officially supported SDK/agent for server-side monitoring of these workloads. You can manually instrument client-side transactions on a PHP or WordPress site by adding the client-side JavaScript to your webpages by using the JavaScript SDK.

The following table provides a more detailed explanation of what these values mean, their underlying causes, and recommended fixes.

Problem value Explanation Fix
AppAlreadyInstrumented:true This value indicates that the extension detected that some aspect of the SDK is already present in the application and will back off. It can be because of a reference to System.Diagnostics.DiagnosticSource, Microsoft.AspNet.TelemetryCorrelation, or Microsoft.ApplicationInsights. Remove the references. Some of these references are added by default from certain Visual Studio templates. Older versions of Visual Studio might add references to Microsoft.ApplicationInsights.
AppAlreadyInstrumented:true This value can also be caused by the presence of the preceding DLLs in the app folder from a previous deployment. Clean the app folder to ensure that these DLLs are removed. Check both your local app's bin directory and the wwwroot directory on the App Service resource. To check the wwwroot directory of your App Service web app, select Advanced Tools (Kudu) > Debug console > CMD > home\site\wwwroot.
AppContainsAspNetTelemetryCorrelationAssembly: true This value indicates that the extension detected references to Microsoft.AspNet.TelemetryCorrelation in the application and will back off. Remove the reference.
AppContainsDiagnosticSourceAssembly**:true This value indicates that the extension detected references to System.Diagnostics.DiagnosticSource in the application and will back off. For ASP.NET, remove the reference.
IKeyExists:false This value indicates that the instrumentation key isn't present in the app setting APPINSIGHTS_INSTRUMENTATIONKEY. Possible causes might be that the values were accidentally removed, or you forgot to set the values in the automation script. Make sure the setting is present in the App Service application settings.

System.IO.FileNotFoundException after 2.8.44 upgrade

The 2.8.44 version of autoinstrumentation upgrades Application Insights SDK to 2.20.0. The Application Insights SDK has an indirect reference to System.Runtime.CompilerServices.Unsafe.dll through System.Diagnostics.DiagnosticSource.dll. If the application has binding redirect for System.Runtime.CompilerServices.Unsafe.dll and if this library isn't present in the application folder, it might throw System.IO.FileNotFoundException.

To resolve this issue, remove the binding redirect entry for System.Runtime.CompilerServices.Unsafe.dll from the web.config file. If the application wanted to use System.Runtime.CompilerServices.Unsafe.dll, set the binding redirect as shown here:

	<assemblyIdentity name="System.Runtime.CompilerServices.Unsafe" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />
	<bindingRedirect oldVersion="" newVersion="" />

As a temporary workaround, you could set the app setting ApplicationInsightsAgent_EXTENSION_VERSION to a value of 2.8.37. This setting will trigger App Service to use the old Application Insights extension. Temporary mitigations should only be used as an interim.

Release notes

For the latest updates and bug fixes, see the release notes.

Next steps