Azure App Service
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How to disable adaptive sampling in Application Insights for .NET Core Web App using environment variables?
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Daniel-4204
105
Reputation points
We are running a .NET Core API (written in C#) hosted in Azure App Service, and using Application Insights for telemetry and diagnostic logging. We’ve been missing certain telemetry entries when under load, and suspect this is due to adaptive sampling being enabled by default.
I’ve found documentation suggesting that adaptive sampling can be disabled by setting an environment variable like: (https://learn.microsoft.com/en-us/azure/azure-monitor/app/java-standalone-sampling-overrides)
APPINSIGHTS_SAMPLING_PERCENTAGE = 100
I added this as an environment variable under Configuration > Application Settings in the Azure Web App and restarted the service before the weekend. However, I’m still seeing the following message in Application Insights:
“Data received from your application is being sampled to reduce the volume of telemetry data retained; only sampled documents will be returned. The sampling may be applied by the Application Insights SDK or on ingestion by Application Insights.”
Additionally, the sampling rate under the Usage and Costs blade in Application Insights to 100%, but I understand that this doesn’t impact SDK-level sampling.
I’m now wondering:
- Are enviroment variables like APPINSIGHTS_SAMPLING_PERCENTAGE even supported for .NET Core SDKs or does this just apply to Java? Because the only suppor doc mentioning using an Envirpment Variable appears to be for Java.
- Or must sampling be disabled explicitly in code for dotnetcore bassed apps?
- Is there an alternative environment variable that applies to .NET Core (not Java/Node)?
My goal is to disable adaptive sampling without changing the app code so we can dynamically control this through configuration only.
Azure App Service
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Shree Hima Bindu Maganti 6,200 Reputation points Microsoft External Staff Moderator2025-06-30T16:37:57.66+00:00 Hi @Daniel-4204
To disable adaptive sampling in Application Insights for a .NET Core Web App using environment variables,Set the
MicrosoftAppInsights_AdaptiveSamplingTelemetryProcessor_MinSamplingPercentageto100. This effectively disables adaptive sampling.You can also set
MicrosoftAppInsights_AdaptiveSamplingTelemetryProcessor_InitialSamplingPercentageto100to ensure that no telemetry is sampled initially.These environment variables are specifically designed for .NET Core applications and allow you to control sampling behavior without modifying the application code.
References:
- Enable application monitoring in Azure App Service for .NET, Node.js, Python, and Java applications
- Sampling in Application Insight
Let me know if you have any further assistances needed.
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Daniel-4204 105 Reputation points
2025-07-01T16:04:52.8766667+00:00 Thank you for the reply with the additional 2 varibles to set. I set this variables this morning as shown in the image, applied them and restarted the web application. After waiting 4 hours, I reviewed Application Insights for the Web App for the last 3 hours and I am still seeing the Sampling Warning Banner. Is this normal behavior to still see the warning, even with the varibles set? See attahed images.
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Shree Hima Bindu Maganti 6,200 Reputation points Microsoft External Staff Moderator
2025-07-01T18:17:56.4333333+00:00 Hi @Daniel-4204
To disable adaptive sampling in Application Insights for a .NET Core Web App using environment variables, you can set the following variable in your environment:-
APPLICATIONINSIGHTS_ENABLEADAPTIVESAMPLING=false
After setting this variable, ensure that you restart your application for the changes to take effect. If you continue to see the Sampling Warning Banner after making this change and waiting for a period, it may take some time for the Application Insights data to reflect the updated settings.
It's not uncommon to still see the warning initially, as it may take a while for the telemetry data to update. However, if the warning persists beyond a reasonable timeframe, consider checking your configuration or reviewing the Application Insights logs for any potential issues.
References:
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Daniel-4204 105 Reputation points
2025-07-07T18:47:49.2166667+00:00 @Shree Hima Bindu Maganti I still need a bit of help here. Thanks in advance for any guidance. We’re currently troubleshooting inconsistent request sampling behavior with Application Insights in our ASP.NET Core Web App.
As of July 1st at 2:00 PM CST, we confirmed that all relevant Application Insights environment variables are correctly set in the Web App’s configuration. (note: there aren't any requests on days that show 100 below) The Web App was also restarted to ensure the new settings were applied. We’ve verified the Environment variables set are listed via the Kudu (Advanced Tools) settings blade at: https://app-ourWebAppName-dev.scm.azurewebsites.net/api/settings
I’ve reviewed the codebase, and aside from the single line services.AddApplicationInsightsTelemetry();, there is no additional Application Insights configuration present in the webapp code (See image below). I’ve followed all recommended steps for Environment Varibles (See photo above), and there’s no indication of request throttling. This is a development environment but we are using production (P0v3) webapp service plans (not basic) with minimal traffic, so we would expect 100% of telemetry to be ingested.
Thank you in advance for any additional info you can provide.
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Shree Hima Bindu Maganti 6,200 Reputation points Microsoft External Staff Moderator
2025-07-09T16:44:10.2833333+00:00 Hi @Daniel-4204
Apology for your inconvenience
Microsoft.ApplicationInsights.AspNetCore 1.0.2)Currently, this is these are the only configuration I can find and there isn't anything on sampling:
var appInsightsConfiguration = new ConfigurationBuilder() .AddApplicationInsightsSettings( developerMode: false, instrumentationKey: Configuration["ApplicationInsights:InstrumentationKey"]) .Build(); services.AddApplicationInsightsTelemetry(appInsightsConfiguration);You can disable sampling by using the
ApplicationInsightsServiceOptions class.var aiOptions = new Microsoft.ApplicationInsights.AspNetCore.Extensions.ApplicationInsightsServiceOptions(); aiOptions.EnableAdaptiveSampling = false; services.AddApplicationInsightsTelemetry(Configuration, aiOptions);https://stackoverflow.com/questions/40156377/disable-application-insights-sampling-with-the-asp-net-core-libraries?rq=4
https://learn.microsoft.com/en-us/previous-versions/azure/azure-monitor/app/sampling-classic-apiLet me know if you have any further assistance needed.
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Daniel-4204 105 Reputation points
2025-07-09T19:21:02.62+00:00 @Shree Hima Bindu Maganti Thank you very much for the information; much appreciated. Would you mind reviewing this below and offering a second opinion?
From what I can tell, the environment variables you provided aren't having an effect on the sampling behavior in our application. I am starting to suspect this may be due to the app using a legacy Application Insights package with .NETCore.
As I mentioned earlier, I reviewed the codebase and aside from a single line "services.AddApplicationInsightsTelemetry();" and there’s no additional Application Insights configuration present in the web app (see image below).
Based on this Microsoft documentation (link below), it seems we should consider migrating to the newer OpenTelemetry instrumentation libraries. That said, I haven’t been able to find definitive guidance in a Microsoft Doc on whether the Environment Variables in question are supported under the legacy SDK, OpenTelemetry, or both. I am guessing they are just valid for OpenTelemetry...
https://learn.microsoft.com/en-us/azure/azure-monitor/app/opentelemetry-dotnet-migrate?tabs=aspnetcoreDo you have any insight on this? Is this the reason that the Environment Variables have no bearing on our telemetry behaivor?
Thanks again,
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Shree Hima Bindu Maganti 6,200 Reputation points Microsoft External Staff Moderator
2025-07-10T18:51:41.1633333+00:00 Hi @Daniel-4204
Apology for your inconvenience
To disable adaptive sampling in Application Insights for a .NET Core web application using environment variables, you typically need to set the appropriate environment variable for the Application Insights SDK. However, if you are using a legacy Application Insights package, the environment variables may not have the desired effect, as they are primarily supported in the newer OpenTelemetry instrumentation libraries.From the context, it appears that the legacy SDK does not support the same configuration options as the newer versions, which could explain why the environment variables you set are not impacting the sampling behavior. Migrating to the newer OpenTelemetry libraries is recommended for better support and features, including the ability to configure adaptive sampling through environment variables.
If your application is still using the legacy SDK and lacks additional configuration, it may not recognize the environment variables as intended. Therefore, confirming the SDK version and considering an upgrade would be a prudent step.
References:
- Sampling in Application Insights
- OpenTelemetry Support and Feedback for Application Insights
Let me know if you have any further assistance needed.
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Shree Hima Bindu Maganti 6,200 Reputation points Microsoft External Staff Moderator
2025-07-14T17:37:46.52+00:00 Hi @Daniel-4204
Just checking in to see if information in comment was helpful. If you have any further updates on this issue, please feel free to post/comment back. -
Daniel-4204 105 Reputation points
2025-07-21T14:33:20.2+00:00 @Shree Hima Bindu Maganti Thank you, Apologies for the delayed response. I believe the information provided was helpful. However, I’m unable to confirm whether the issue is fully resolved, as migrating to OpenTelemetry requires changes to the application code making it a future-to-do effort. That said, we’ve added the migration to our DevOps backlog and plan to implement it in a future update. If this support forum allows then, I’ll post an update once the migration is complete to confirm whether this solution worked for us.
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Shree Hima Bindu Maganti 6,200 Reputation points Microsoft External Staff Moderator
2025-07-21T18:20:07.9333333+00:00 Hi @Daniel-4204
Thanks for your Update.
Let me know if you have any further assistances needed. -
Daniel-4204 105 Reputation points
2025-10-21T16:32:05.3266667+00:00 Shree, As of recently, I can confirm that OpenTelemetry has been adopted in the Azure Web Apps previously discussed in this thread. The development team has migrated away from the legacy codebase, and features like Live Metrics are now working.
Unfortunately, the Environment Variables you previously suggested have still not resolved the issue now that OpenTelemetry is in use. Application Insights is still believed to be sampling lower than 100%, as shown in the attached logs.
What steps can be taken now to ensure that all HTTP requests to the Web App are consistently captured in Application Insights, as previously discussed? Thank you for your help with this.
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