Application performance FAQs for Web Apps in Azure

Article
10/04/2022

Note

Some of the below guidelines might only work on Windows or Linux App Services. For example, Linux App Services run in 64-bit mode by default.

This article has answers to frequently asked questions (FAQs) about application performance issues for the Web Apps feature of Azure App Service.

If your Azure issue is not addressed in this article, visit the Azure forums on MSDN and Stack Overflow. You can post your issue in these forums, or post to @AzureSupport on Twitter. You also can submit an Azure support request. To submit a support request, on the Azure support page, select Get support.

Why is my App Service Plan displaying CPU/Memory usage even when all Web Apps are stopped?

Azure App Service requires continuous system processes that handle several platform operations and features, such as security updates, availability of the SCM console, application monitoring, authentication, and many other vital features of your Web App.

System processes will run on App Service Plans even if there are no Web Apps running or if the App Service Plan contains no Web Apps.

The platform processes will consume a minimum amount of resources (such as CPU, Memory and Disk space), and the same should be accounted during the capacity planning, monitoring, and auto-scaling trigger configuration of an App Service Plan.

Why is my app slow?

Multiple factors might contribute to slow app performance. For detailed troubleshooting steps, see Troubleshoot slow web app performance.

How do I troubleshoot a high CPU-consumption scenario?

In some high CPU-consumption scenarios, your app might truly require more computing resources. In that case, consider scaling to a higher service tier so the application gets all the resources it needs. Other times, high CPU consumption might be caused by a bad loop or by a coding practice. Getting insight into what's triggering increased CPU consumption is a two-part process. First, create a process dump, and then analyze the process dump. For more information, see Capture and analyze a dump file for high CPU consumption for Web Apps.

How do I troubleshoot a high memory-consumption scenario?

In some high memory-consumption scenarios, your app might truly require more computing resources. In that case, consider scaling to a higher service tier so the application gets all the resources it needs. Other times, a bug in the code might cause a memory leak. A coding practice also might increase memory consumption. Getting insight into what's triggering high memory consumption is a two-part process. First, create a process dump, and then analyze the process dump. Crash Diagnoser from the Azure Site Extension Gallery can efficiently perform both these steps. For more information, see Capture and analyze a dump file for intermittent high memory for Web Apps.

How do I automate App Service web apps by using PowerShell?

You can use PowerShell cmdlets to manage and maintain App Service web apps. In our blog post Automate web apps hosted in Azure App Service by using PowerShell, we describe how to use Azure Resource Manager-based PowerShell cmdlets to automate common tasks. The blog post also has sample code for various web apps management tasks. For descriptions and syntax for all App Service web apps cmdlets, see Az.Websites.

How do I view my web app's event logs?

To view your web app's event logs:

Sign in to your Kudu website (https://*yourwebsitename*.scm.azurewebsites.net).
In the menu, select Debug Console > CMD.
Select the LogFiles folder.
To view event logs, select the pencil icon next to eventlog.xml.
To download the logs, run the PowerShell cmdlet Save-AzureWebSiteLog -Name webappname.

How do I capture a user-mode memory dump of my web app?

To capture a user-mode memory dump of your web app:

Sign in to your Kudu website (https://*yourwebsitename*.scm.azurewebsites.net).
Select the Process Explorer menu.
Right-click the w3wp.exe process or your WebJob process.
Select Download Memory Dump > Full Dump.

How do I view process-level info for my web app?

You have two options for viewing process-level information for your web app:

In the Azure portal:
1. Open the Process Explorer for the web app.
2. To see the details, select the w3wp.exe process.
In the Kudu console:
1. Sign in to your Kudu website (https://*yourwebsitename*.scm.azurewebsites.net).
2. Select the Process Explorer menu.
3. For the w3wp.exe process, select Properties.

When I browse to my app, I see "Error 403 - This web app is stopped." How do I resolve this?

Three conditions can cause this error:

The web app has reached a billing limit and your site has been disabled.
The web app has been stopped in the portal.
The web app has reached a resource quota limit that might apply to a Free or Shared scale service plan.

To see what is causing the error and to resolve the issue, follow the steps in Web Apps: "Error 403 – This web app is stopped".

Where can I learn more about quotas and limits for various App Service plans?

For information about quotas and limits, see App Service limits.

How do I decrease the response time for the first request after idle time?

By default, web apps are unloaded if they're idle for a set period of time. This way, the system can conserve resources. The downside is that the response to the first request after the web app is unloaded is longer, to allow the web app to load and start serving responses. In Basic and Standard service plans, you can turn on the Always On setting to keep the app always loaded. This eliminates longer load times after the app is idle. To change the Always On setting:

In the Azure portal, go to your web app.
Select Configuration
Select General settings.
For Always On, select On.

How do I turn on failed request tracing?

To turn on failed request tracing, follow these steps:

In the Azure portal, go to your web app.
Select All Settings > Diagnostics Logs.
For Failed Request Tracing, select On.
Select Save.
On the web app blade, select Tools.
Select Visual Studio Online.
If the setting isn't On, select On.
Select Go.
Select Web.config.

In system.webServer, add the following configuration (to capture a specific URL):

<system.webServer>
<tracing> <traceFailedRequests>
<remove path="*api*" />
<add path="*api*">
<traceAreas>
<add provider="ASP" verbosity="Verbose" />
<add provider="ASPNET" areas="Infrastructure,Module,Page,AppServices" verbosity="Verbose" />
<add provider="ISAPI Extension" verbosity="Verbose" />
<add provider="WWW Server" areas="Authentication,Security,Filter,StaticFile,CGI,Compression, Cache,RequestNotifications,Module,FastCGI" verbosity="Verbose" />
</traceAreas>
<failureDefinitions statusCodes="200-999" />
</add> </traceFailedRequests>
</tracing>

To troubleshoot slow-performance issues, add this configuration (if the capturing request is taking more than 30 seconds):

<system.webServer>
<tracing> <traceFailedRequests>
<remove path="*" />
<add path="*">
<traceAreas> <add provider="ASP" verbosity="Verbose" />
<add provider="ASPNET" areas="Infrastructure,Module,Page,AppServices" verbosity="Verbose" />
<add provider="ISAPI Extension" verbosity="Verbose" />
<add provider="WWW Server" areas="Authentication,Security,Filter,StaticFile,CGI,Compression, Cache,RequestNotifications,Module,FastCGI" verbosity="Verbose" />
</traceAreas>
<failureDefinitions timeTaken="00:00:30" statusCodes="200-999" />
</add> </traceFailedRequests>
</tracing>

To download the failed request traces, in the portal, go to your website.
Select Tools > Kudu > Go.
In the menu, select Debug Console > CMD.
Select the LogFiles folder, and then select the folder with a name that starts with W3SVC.
To see the XML file, select the pencil icon.

I see the message "Worker Process requested recycle due to 'Percent Memory' limit." How do I address this issue?

The maximum available amount of memory for a 32-bit process (even on a 64-bit operating system) is 2 GB. By default, the worker process is set to 32-bit in App Service (for compatibility with legacy web applications).

Consider switching to 64-bit processes so you can take advantage of the additional memory available in your Web Worker role. This action triggers a web app restart, so schedule accordingly.

Also note that a 64-bit environment requires a Basic or Standard service plan. Free and Shared plans always run in a 32-bit environment.

For more information, see Configure web apps in App Service.

Why does my request time out after 230 seconds?

Azure Load Balancer has a default idle timeout setting of four minutes. This setting is generally a reasonable response time limit for a web request. so, App Service returns a timeout to the client if your application does not return a response within approximately 240 seconds (230 seconds on Windows app, 240 seconds on Linux app).　If your web app requires background processing, we recommend using Azure WebJobs. The Azure web app can call WebJobs and be notified when background processing is finished. You can choose from multiple methods for using WebJobs, including queues and triggers.

WebJobs is designed for background processing. You can do as much background processing as you want in a WebJob. For more information about WebJobs, see Run background tasks with WebJobs.

ASP.NET Core applications that are hosted in App Service sometimes stop responding. How do I fix this issue?

A known issue with an earlier Kestrel version might cause an ASP.NET Core 1.0 app that's hosted in App Service to intermittently stop responding. You also might see this message: "The specified CGI Application encountered an error and the server terminated the process."

This issue is fixed in Kestrel version 1.0.2. This version is included in the ASP.NET Core 1.0.3 update. To resolve this issue, make sure you update your app dependencies to use Kestrel 1.0.2. Alternatively, you can use one of two workarounds that are described in the blog post ASP.NET Core 1.0 slow perf issues in App Service web apps.

I can't find my log files in the file structure of my web app. How can I find them?

If you use the Local Cache feature of App Service, the folder structure of the LogFiles and Data folders for your App Service instance are affected. When Local Cache is used, subfolders are created in the storage LogFiles and Data folders. The subfolders use the naming pattern "unique identifier" + time stamp. Each subfolder corresponds to a VM instance in which the web app is running or has run.

To determine whether you're using Local Cache, check your App Service Application settings tab. If Local Cache is being used, the app setting WEBSITE_LOCAL_CACHE_OPTION is set to Always.

If you aren't using Local Cache and are experiencing this issue, submit a support request.

I see the message "An attempt was made to access a socket in a way forbidden by its access permissions." How do I resolve this error?

This error typically occurs if the outbound TCP connections on the VM instance are exhausted. In App Service, limits are enforced for the maximum number of outbound connections that can be made for each VM instance. For more information, see Cross-VM numerical limits.

This error also might occur if you try to access a local address from your application. For more information, see Local address requests.

For more information about outbound connections in your web app, see the blog post about outgoing connections to Azure websites.

How do I use Visual Studio to remote debug my App Service web app?

For a detailed walkthrough that shows you how to debug your web app by using Visual Studio, see Remote debug your App Service web app.

Contact us for help

If you have questions or need help, create a support request, or ask Azure community support. You can also submit product feedback to Azure feedback community.