Runtime error on Azure Web App

Question

Runtime error on Azure Web App

Mark Pearson 40

Hi,

We have a web that that is throwing a runtime error when trying to visit the page. The Azure ran troubleshooter is showing the following:

HTTP Server Errors Detected

HTTP Servers errors indicate something wrong either with Application code or by the platform serving the requests. The below table shows you the count of all HTTP Servers errors that happened on the instance serving your app.

The below table shows you the count of HTTP Errors by the module setting the error code.

|FailingModule|HttpStatus|FailedRequestCount|Description| |ManagedPipelineHandler|500.0|2182|| |__DynamicModule_System.Web.WebPages.WebPageHttpModule|500.0|196|| |Session|500.0|22||

Handler descriptions:

ManagedPipelineHandler - ManagedPipelineHandler is the handler used by ASP.NET to serve managed requests. Errors set by this handler would typically mean application code encountering an un-handled exception.

The below table shows failed requests grouped by their request execution time.

|HttpStatus|HttpSubStatus|FailedRequests|50thPercentile|90thPercentile|95thPercentile|99thPercentile| |500|0|1329|0 sec|2 sec|18 sec|18 sec| |503|0|7|0 sec|0 sec|0 sec|0 sec|We have attempted to restart the web app, but continue to see this error. Any and all help appreciated on this matter.

Prabhavathi Manchala 2,315 Reputation points Microsoft External Staff Moderator

2025-06-09T09:33:00.6266667+00:00
Hi Mark Pearson,

Your web app is currently encountering a high number of HTTP 500.0 errors, which means something is failing within your application code. Specifically, the ManagedPipelineHandler is reporting most of the errors, which tells us that ASP.NET is hitting unhandled exceptions during request execution.

From the diagnostic logs:

Over 2,300 total 500 errors, with ManagedPipelineHandler responsible for 2,182.

Some errors also coming from System.Web.WebPages.WebPageHttpModule and Session modules.

Response times are high (95th percentile = 18 seconds), which may indicate performance bottlenecks or timeouts.

The root cause of the HTTP 500.0 errors is an unhandled exception in your application code. Most of the failures are coming from ASP.NET’s ManagedPipelineHandler, which suggests issues like a code bug, missing configuration, database connection failure, or resource exhaustion (e.g., memory or threads). Restarting the app might give temporary relief but won't resolve the underlying problem.

1). Enable Detailed Error Messages for Debugging

To see the actual exception instead of a generic 500 error, enable detailed errors by adding this to your web.config

<system.web> <customErrors mode="Off"/> <compilation debug="true"/> </system.web> <system.webServer> <httpErrors errorMode="Detailed"/> </system.webServer>

HTTP Detailed Errors in IIS

2). Review Application Logs for Stack Trace

Use Application Insights or Log Stream to check what’s triggering the 500s.

Go to Azure Portal -> App Service -> Monitoring -> Log Stream.

Or check Application Insights -> Failures -> Exceptions for exact line of failure.

Diagnose exceptions in web apps with Application Insights

3). Check for Dependency Failures (SQL, Redis, External APIs)

500 errors often occur due to incorrect SQL connection strings, unavailable databases, failing APIs, or missing app settings like secrets or config keys.

Ensure connection strings are correct, Key Vault/settings are accessible and valid, and requests aren't timing out due to slowness.

Monitor Azure App Service

4). Monitor App Plan Resources

Long response times (up to 18 seconds) may indicate memory or CPU overload, or thread pool exhaustion.

Use the App Service Plan metrics to check usage:

Go to Azure Portal > App Service Plan > Metrics.

Check Memory Working Set, CPU, and HTTP Queue Length.

5). Use Azure App Service Diagnostics Tool

Use the "Diagnose and solve problems" tool in the Azure Portal:

Go to Web App > Diagnose and solve problems > Availability and Performance > HTTP 5xx Errors.

Azure will automatically detect bottlenecks, crashes, and even suggest code-level fixes.

Diagnostics in Azure App Service
Mark Pearson 40 Reputation points

2025-06-09T09:59:16.8533333+00:00

We are seeing the following error on one of our Azure VM's running as a domain controller
Mark Pearson 40 Reputation points

2025-06-09T10:31:45.1833333+00:00

This issue was caused by an Azure VM running as a domain controller. The Azure host the VM was running on had a disk error that triggered a live migration of the VM that had eventually cause the VM to be stuk in the above hung state.

An additional restart triggered another migration that fixed the issue. The Vm started as exoected and then the website became available again shortly afterwards.

Accepted answer

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Mark Pearson 40 Reputation points

2025-06-09T09:59:16.8533333+00:00

We are seeing the following error on one of our Azure VM's running as a domain controller
Mark Pearson 40 Reputation points

2025-06-09T10:31:45.1833333+00:00

This issue was caused by an Azure VM running as a domain controller. The Azure host the VM was running on had a disk error that triggered a live migration of the VM that had eventually cause the VM to be stuk in the above hung state.

An additional restart triggered another migration that fixed the issue. The Vm started as exoected and then the website became available again shortly afterwards.

Answer 1

Hi Mark Pearson,

I'm glad that you were able to resolve your issue and thank you for posting your solution so that others experiencing the same thing can easily reference this!

Since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others ", I'll repost your solution in case you'd like to "Accept " the answer.

Issue:

Runtime error on Azure Web App

Solution:

This issue was caused by an Azure VM running as a domain controller. The Azure host the VM was running on had a disk error that triggered a live migration of the VM that had eventually cause the VM to be stuk in the above hung state.

An additional restart triggered another migration that fixed the issue. The Vm started as exoected and then the website became available again shortly afterwards.

Please click Accept Answer and kindly upvote it so that other people who faces similar issue may get benefitted from it.

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Runtime error on Azure Web App

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