How to Determine Cause of Timeout Exceptions on App Service

Question

How to Determine Cause of Timeout Exceptions on App Service

Shawn Strayer 0

I have a web app called rpm2024r6apiRBI that is sporadically getting timeout exceptions in short periods. I need to know what is causing the timeouts and how to resolve. The latest occurrence was 4/30 @ 10:22.

Michael Taylor 59,341 Reputation points

2025-04-30T20:45:19.0033333+00:00

We have no visibility into your application so we aren't going to be able to provide much guidance without more information. If you're using a standard web framework then hopefully you're using logging to track errors in your app. Thus you'd look at your error logs to help with this.

If you are using AppInsights then refer to the AppInsights log in the Azure Portal.

If you have no logging at all then now might be a good time to start considering it. But in the meantime go to your app service in Azure Portal and then Monitoring tab. Within here you can see recent HTTP events including HTTP response codes and requests and response times. In the case of HTTP errors from your service you can click on the details and then look at what is going on. For requests you can do the same thing. You can drill into the details of exceptions (such as timeouts) to get an idea of what was going on. Depending on your web framework and whether you deploy debug symbols, if applicable, when determine how much or little information you are getting.

If necessary, you can dynamically enable more logging from the Logs tab. This has a cost but might be useful if the other tab doesn't provide enough details.
Kyle Burns 91 Reputation points Microsoft Employee

2025-05-01T13:14:37.0933333+00:00

To extend somewhat on Michael's advice which I agree with completely, you may want to take a little bit of time to check out the following learning module and then apply what you have learned to your issue - https://learn.microsoft.com/en-us/training/paths/az-204-instrument-solutions-support-monitoring-logging/
Kantamsetti Aslesha 250 Reputation points Microsoft External Staff

2025-05-05T05:26:39.1633333+00:00

Hi @Shawn Strayer

Just checking in to see if above information was helpful. If you have any further updates on this issue, please feel free to post back.
Kantamsetti Aslesha 250 Reputation points Microsoft External Staff

2025-05-06T04:45:05.6133333+00:00

Hi @Shawn Strayer
Following up to check if the issue is resolved or if you need any further assistance. Let me know how it's going!
Sampath 2,925 Reputation points Microsoft External Staff Moderator

2025-05-06T08:26:55.29+00:00
Hi @Shawn Strayer,

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. Therefore, 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.

can you check this below steps:

Go to App Service Diagnostics

Choose Diagnostic Tools .

Click on Collect Memory Dump tile and follow the instructions.

check if Local Cache can be enable for their app.

Since you have only one instance you can expect downtime because when the App Service platform is upgraded, the instance on which your web app is running will be upgraded. Therefore, your web app process will be restarted and will experience downtime.

You can find the reasons for Slowest by running the KQL query below.

dependencies | where cloud_RoleName =~ 'rp' | where timestamp >= datetime(2025-04-30 07:20:00) and timestamp <= datetime(2025-05-03 07:20:00) | where type != "sampath" | summarize ["Average Latency (ms)"] = round(avg(duration), 2), ["50th Percentile Latency (ms)"]=round(percentile(duration, 50), 2), ["90th Percentile Latency (ms)"]=round(percentile(duration, 90), 2), ["95th Percentile Latency (ms)"]=round(percentile(duration, 95), 2), ["Total Execution Count"]=count() by name, type | where ["Average Latency (ms)"] > 100 | top 5 by ["Average Latency (ms)"] desc

Your answer

Michael Taylor 59,341 Reputation points

2025-04-30T20:45:19.0033333+00:00

We have no visibility into your application so we aren't going to be able to provide much guidance without more information. If you're using a standard web framework then hopefully you're using logging to track errors in your app. Thus you'd look at your error logs to help with this.

If you are using AppInsights then refer to the AppInsights log in the Azure Portal.

If you have no logging at all then now might be a good time to start considering it. But in the meantime go to your app service in Azure Portal and then Monitoring tab. Within here you can see recent HTTP events including HTTP response codes and requests and response times. In the case of HTTP errors from your service you can click on the details and then look at what is going on. For requests you can do the same thing. You can drill into the details of exceptions (such as timeouts) to get an idea of what was going on. Depending on your web framework and whether you deploy debug symbols, if applicable, when determine how much or little information you are getting.

If necessary, you can dynamically enable more logging from the Logs tab. This has a cost but might be useful if the other tab doesn't provide enough details.
Kyle Burns 91 Reputation points Microsoft Employee

2025-05-01T13:14:37.0933333+00:00

To extend somewhat on Michael's advice which I agree with completely, you may want to take a little bit of time to check out the following learning module and then apply what you have learned to your issue - https://learn.microsoft.com/en-us/training/paths/az-204-instrument-solutions-support-monitoring-logging/
Kantamsetti Aslesha 250 Reputation points Microsoft External Staff

2025-05-05T05:26:39.1633333+00:00

Hi @Shawn Strayer

Just checking in to see if above information was helpful. If you have any further updates on this issue, please feel free to post back.
Kantamsetti Aslesha 250 Reputation points Microsoft External Staff

2025-05-06T04:45:05.6133333+00:00

Hi @Shawn Strayer
Following up to check if the issue is resolved or if you need any further assistance. Let me know how it's going!

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How to Determine Cause of Timeout Exceptions on App Service

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