Threading exception error in azure web app premium

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Threading exception error in azure web app premium

Irukulla, Krishna Priyatham 0

We are facing this issue intermittently and its a FASTAPI app deployed on azure web app and none of our API's take 300secs however we still see this happening intermittently and can't find the root cause.

Failed to forward request to http://********:8000. Encountered a System.Threading.Tasks.TaskCanceledException exception after 300001.1ms with message: The request was canceled due to the configured HttpClient.Timeout of 300 seconds elapsing. Check app

Can someone please help on how to find the root cause for this issue?

Prabhavathi Manchala 810 Reputation points Microsoft External Staff

2025-03-28T06:00:50.9466667+00:00
Hi Irukulla, Krishna Priyatham,

The System.Threading.Tasks.TaskCanceledException occurs when an HTTP request exceeds its timeout period, meaning the application takes longer than expected to process it. Azure has a default timeout of 300 seconds for HTTP requests. Although APIs typically shouldn't take this long, occasional issues can cause delays, leading to request cancellations.

This issue can arise from various factors, such as delays caused by slow external services or databases. Performance problems may also occur when your app experiences high traffic or competes for resources. Thread pool starvation can happen if blocking calls exist in asynchronous code, restricting thread availability. Additionally, high CPU or memory usage can slow down response times, especially during peak traffic or heavy processing.

In your FASTAPI app, you can adjust the timeout value for HTTP requests, but make sure to do this only if longer wait times are necessary for your app.

import httpx async with httpx.AsyncClient(timeout=httpx.Timeout(600)) as client: response = await client.get(....)

Ensure your app's external services, like databases or APIs, are performing efficiently by reviewing database indexes, optimizing queries or evaluating the performance of third-party APIs.

Please check your Azure portal for CPU or memory spikes, review Azure Metrics for any unusual usage or scaling problems during errors and consider turning on auto-scaling to manage changing loads.

Prevent thread pool starvation by checking for blocking calls in async methods and avoiding the use of .Result or .Wait() on tasks, which can lead to deadlocks and thread starvation.

Please review application logs for errors and enable Application Insights in Azure for detailed performance analysis.

https://learn.microsoft.com/en-us/azure/azure-monitor/app/asp-net-core#enable-application-insights-server-side-telemetry-visual-studio
Prabhavathi Manchala 810 Reputation points Microsoft External Staff

2025-03-31T06:30:15.9633333+00:00

Hi Irukulla, Krishna Priyatham,

We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution, please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.
Irukulla, Krishna Priyatham 0 Reputation points

2025-03-31T21:04:55.6033333+00:00

@Prabhavathi Manchala I've checked all these things and I can confirm that we use async api's but we dont have any blocking code in it for example we use aioodbc to talk to msql via async, we use aiofiles to do read and write and we use async version of redis-py to talk to redis server. Apart from this, None of our API's take more than 8-9 secs at max and there is no chance of 300secs wait time for some of them to return the response.

We are not facing this issue on our local even when performing load tesing using locust.
Prabhavathi Manchala 810 Reputation points Microsoft External Staff

2025-04-01T19:01:44.65+00:00
Hi Irukulla, Krishna Priyatham,

Your app may experience timeouts during traffic spikes if Azure can't scale fast enough, causing resource limits (CPU/memory) to be hit. External services like databases or Redis could sometimes slow down, adding to delays. Azure may also face scaling delays or resource allocation issues under heavy traffic. If your App Service Plan has limited resources, it may struggle with high demand, causing timeouts.

Enable Application Insights to track your app’s performance in Azure and identify delays or failures. Review key metrics like request duration, database/Redis calls, and failed requests to troubleshoot issues.

Scale your Azure Web App to handle peak traffic and resource contention. You can do this by upgrading plan tiers or enabling auto-scaling based on CPU and memory usage.

https://learn.microsoft.com/en-us/azure/app-service/manage-scale-up#scale-up-your-pricing-tier

If the issue occurs intermittently in Azure but not during local load testing, it may be due to network latency between your app and external services; use Azure Network Watcher to diagnose the problem.

Please review the connection pool settings for each service to ensure they are properly configured, especially for SQL Server and Redis, to prevent delays during high traffic.
Prabhavathi Manchala 810 Reputation points Microsoft External Staff

2025-04-03T01:18:51.06+00:00

Hi Irukulla, Krishna Priyatham,

We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution, please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.
Irukulla, Krishna Priyatham 0 Reputation points

2025-04-03T02:33:31.3966667+00:00

Hello, we havent yet found the resolution and will let u know once after we fix it. However, Its very undeterministic to identify why its happening as we dont see any over cpu/memory usage and we dont see that either in our db/redis.
Prabhavathi Manchala 810 Reputation points Microsoft External Staff

2025-04-03T18:01:59.3433333+00:00

Hi Irukulla, Krishna Priyatham,

This issue may be due to network conditions or platform behavior. If you have any further queries on this issue, please feel free to post back.

Your answer

Prabhavathi Manchala 810 Reputation points Microsoft External Staff

2025-03-31T06:30:15.9633333+00:00

Hi Irukulla, Krishna Priyatham,

We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution, please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.
Irukulla, Krishna Priyatham 0 Reputation points

2025-03-31T21:04:55.6033333+00:00

@Prabhavathi Manchala I've checked all these things and I can confirm that we use async api's but we dont have any blocking code in it for example we use aioodbc to talk to msql via async, we use aiofiles to do read and write and we use async version of redis-py to talk to redis server. Apart from this, None of our API's take more than 8-9 secs at max and there is no chance of 300secs wait time for some of them to return the response.

We are not facing this issue on our local even when performing load tesing using locust.
Prabhavathi Manchala 810 Reputation points Microsoft External Staff

2025-04-01T19:01:44.65+00:00

Hi Irukulla, Krishna Priyatham,

Your app may experience timeouts during traffic spikes if Azure can't scale fast enough, causing resource limits (CPU/memory) to be hit. External services like databases or Redis could sometimes slow down, adding to delays. Azure may also face scaling delays or resource allocation issues under heavy traffic. If your App Service Plan has limited resources, it may struggle with high demand, causing timeouts.

Enable Application Insights to track your app’s performance in Azure and identify delays or failures. Review key metrics like request duration, database/Redis calls, and failed requests to troubleshoot issues.

Scale your Azure Web App to handle peak traffic and resource contention. You can do this by upgrading plan tiers or enabling auto-scaling based on CPU and memory usage.

https://learn.microsoft.com/en-us/azure/app-service/manage-scale-up#scale-up-your-pricing-tier

If the issue occurs intermittently in Azure but not during local load testing, it may be due to network latency between your app and external services; use Azure Network Watcher to diagnose the problem.

Please review the connection pool settings for each service to ensure they are properly configured, especially for SQL Server and Redis, to prevent delays during high traffic.
Prabhavathi Manchala 810 Reputation points Microsoft External Staff

2025-04-03T01:18:51.06+00:00

Hi Irukulla, Krishna Priyatham,

We haven’t heard from you on the last response and was just checking back to see if you have a resolution yet. In case if you have any resolution, please do share that same with the community as it can be helpful to others. Otherwise, will respond with more details and we will try to help.
Irukulla, Krishna Priyatham 0 Reputation points

2025-04-03T02:33:31.3966667+00:00

Hello, we havent yet found the resolution and will let u know once after we fix it. However, Its very undeterministic to identify why its happening as we dont see any over cpu/memory usage and we dont see that either in our db/redis.
Prabhavathi Manchala 810 Reputation points Microsoft External Staff

2025-04-03T18:01:59.3433333+00:00

Hi Irukulla, Krishna Priyatham,

This issue may be due to network conditions or platform behavior. If you have any further queries on this issue, please feel free to post back.

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Threading exception error in azure web app premium

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