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Debug exceptions in .NET applications using Snapshot Debugger

  • Article

With Snapshot Debugger, you can automatically collect a debug snapshot when an exception occurs in your live .NET application. Debug snapshots collected show the state of source code and variables at the moment the exception was thrown.

The Snapshot Debugger in Application Insights:

  • Monitors system-generated logs from your web app.
  • Collects snapshots on your top-throwing exceptions.
  • Provides information you need to diagnose issues in production.

Learn more about the Snapshot Debugger and Snapshot Uploader processes.

Supported applications and environments

This section lists the applications and environments that are supported.

Applications

Snapshot collection is available for:

Environments

The following environments are supported:

Note

Client applications (for example, WPF, Windows Forms, or UWP) aren't supported.

Prerequisites for using Snapshot Debugger

Packages and configurations

Permissions

How Snapshot Debugger works

The Snapshot Debugger is implemented as an Application Insights telemetry processor. When your application runs, the Snapshot Debugger telemetry processor is added to your application's system-generated logs pipeline.

Important

Snapshots might contain personal data or other sensitive information in variable and parameter values. Snapshot data is stored in the same region as your Application Insights resource.

Snapshot Debugger process

The Snapshot Debugger process starts and ends with the TrackException method. A process snapshot is a suspended clone of the running process, so that your users experience little to no interruption.

  1. Your application throws the TrackException.

  2. The Snapshot Debugger monitors exceptions as they're thrown by subscribing to the AppDomain.CurrentDomain.FirstChanceException event.

  3. A counter is incremented for the problem ID.

    • When the counter reaches the ThresholdForSnapshotting value, the problem ID is added to a collection plan.

    Note

    The ThresholdForSnapshotting default minimum value is 1. With this value, your app has to trigger the same exception twice before a snapshot is created.

  4. The exception event's problem ID is computed and compared against the problem IDs in the collection plan.

  5. If there's a match between problem IDs, a snapshot of the running process is created.

    • The snapshot is assigned a unique identifier and the exception is stamped with that identifier.

    Note

    The snapshot creation rate is limited by the SnapshotsPerTenMinutesLimit setting. By default, the limit is one snapshot every 10 minutes.

  6. After the FirstChanceException handler returns, the thrown exception is processed as normal.

  7. The exception reaches the TrackException method again and is reported to Application Insights, along with the snapshot identifier.

Note

Set IsEnabledInDeveloperMode to true if you want to generate snapshots while you debug in Visual Studio.

Snapshot Uploader process

While the Snapshot Debugger process continues to run and serve traffic to users with little interruption, the snapshot is handed off to the Snapshot Uploader process. The Snapshot Uploader:

  1. Creates a minidump.

  2. Uploads the minidump to Application Insights, along with any relevant symbol (.pdb) files.

Note

No more than 50 snapshots per day can be uploaded.

If you enabled the Snapshot Debugger but you aren't seeing snapshots, see the Troubleshooting guide.

Limitations

This section discusses limitations for the Snapshot Debugger.

  • Data retention

    Debug snapshots are stored for 15 days. The default data retention policy is set on a per-application basis. If you need to increase this value, you can request an increase by opening a support case in the Azure portal. For each Application Insights instance, a maximum number of 50 snapshots are allowed per day.

  • Publish symbols

    The Snapshot Debugger requires symbol files on the production server to:

    • Decode variables
    • Provide a debugging experience in Visual Studio

    By default, Visual Studio 2017 versions 15.2+ publishes symbols for release builds when it publishes to App Service.

    In prior versions, you must add the following line to your publish profile .pubxml file so that symbols are published in release mode:

         <ExcludeGeneratedDebugSymbol>False</ExcludeGeneratedDebugSymbol>

    For Azure Compute and other types, make sure that the symbol files are either:

    • In the same folder of the main application .dll (typically, wwwroot/bin), or
    • Available on the current path.

    For more information on the different symbol options that are available, see the Visual Studio documentation. For best results, we recommend that you use Full, Portable, or Embedded.

  • Optimized builds

    In some cases, local variables can't be viewed in release builds because of optimizations applied by the JIT compiler.

    However, in App Service, the Snapshot Debugger can deoptimize throwing methods that are part of its collection plan.

    Tip

    Install the Application Insights Site extension in your instance of App Service to get deoptimization support.

Next steps

Enable the Application Insights Snapshot Debugger for your application:

Release notes for Microsoft.ApplicationInsights.SnapshotCollector

This section contains the release notes for the Microsoft.ApplicationInsights.SnapshotCollector NuGet package for .NET applications, which is used by the Application Insights Snapshot Debugger.

Learn more about the Application Insights Snapshot Debugger for .NET applications.

For bug reports and feedback, open an issue on GitHub.

Note

On March 31, 2025, support for instrumentation key ingestion will end. Instrumentation key ingestion will continue to work, but we'll no longer provide updates or support for the feature. Transition to connection strings to take advantage of new capabilities.

1.4.6

A point release to address a regression when using .NET 8 applications.

Bug fixes

  • Exceptions thrown from dynamically generated methods (e.g. compiled expression trees) in .NET 8 are not being tracked correctly. Fixed.

1.4.5

A point release to address a user-reported bug.

Bug fixes

  • Fixed AccessViolationException when reading some PDBs.

Changes

  • Added a ReadMe to the NuGet package.
  • Updated msdia140.dll.

1.4.4

A point release to address user-reported bugs.

Bug fixes

Changes

  • Lowered PDB scan failure messages from Error to Warning.
  • Updated msdia140.dll.
  • Avoid making a service connection if the debugger is disabled via site extension settings.

1.4.3

A point release to address user-reported bugs.

Bug fixes

1.4.2

A point release to address a user-reported bug.

Bug fixes

Fixed ArgumentException: Delegates must be of the same type.

1.4.1

A point release to revert a breaking change introduced in 1.4.0.

Bug fixes

Fixed Method not found in WebJobs.

1.4.0

Addressed multiple improvements and added support for Microsoft Entra authentication for Application Insights ingestion.

Changes

  • Reduced Snapshot Collector package size by 60% from 10.34 MB to 4.11 MB.
  • Targeted netstandard2.0 only in Snapshot Collector.
  • Bumped Application Insights SDK dependency to 2.15.0.
  • Added back MinidumpWithThreadInfo when writing dumps.
  • Added CompatibilityVersion to improve synchronization between the Snapshot Collector agent and the Snapshot Uploader on breaking changes.
  • Changed SnapshotUploader LogFile naming algorithm to avoid excessive file I/O in App Service.
  • Added pid, role name, and process start time to uploaded blob metadata.
  • Used System.Diagnostics.Process in Snapshot Collector and Snapshot Uploader.

New features

Added Microsoft Entra authentication to SnapshotCollector. To learn more about Microsoft Entra authentication in Application Insights, see Microsoft Entra authentication for Application Insights.

1.3.7.5

A point release to backport a fix from 1.4.0-pre.

Bug fixes

Fixed ObjectDisposedException on shutdown.

1.3.7.4

A point release to address a problem discovered in testing the App Service codeless attach scenario.

Changes

The netcoreapp3.0 target now depends on Microsoft.ApplicationInsights.AspNetCore >= 2.1.1 (previously >= 2.1.2).

1.3.7.3

A point release to address a couple of high-impact issues.

Bug fixes

  • Fixed PDB discovery in the wwwroot/bin folder, which was broken when we changed the symbol search algorithm in 1.3.6.
  • Fixed noisy ExtractWasCalledMultipleTimesException in telemetry.

1.3.7

Changes

The netcoreapp2.0 target of SnapshotCollector depends on Microsoft.ApplicationInsights.AspNetCore >= 2.1.1 (again). This change reverts behavior to how it was before 1.3.5. We tried to upgrade it in 1.3.6, but it broke some App Service scenarios.

New features

Snapshot Collector reads and parses the ConnectionString from the APPLICATIONINSIGHTS_CONNECTION_STRING environment variable or from the TelemetryConfiguration. Primarily, it's used to set the endpoint for connecting to the Snapshot service. For more information, see the Connection strings documentation.

Bug fixes

Switched to using HttpClient for all targets except net45 because WebRequest was failing in some environments because of an incompatible SecurityProtocol (requires TLS 1.2).

1.3.6

Changes

  • SnapshotCollector now depends on Microsoft.ApplicationInsights >= 2.5.1 for all target frameworks. This requirement might be a breaking change if your application depends on an older version of the Microsoft.ApplicationInsights SDK.
  • Removed support for TLS 1.0 and 1.1 in Snapshot Uploader.
  • Period of PDB scans now defaults 24 hours instead of 15 minutes. Configurable via PdbRescanInterval on SnapshotCollectorConfiguration.
  • PDB scan searches top-level folders only, instead of recursive. This change might be a breaking change if your symbols are in subfolders of the binary folder.

New features

  • Log rotation in SnapshotUploader to avoid filling the logs folder with old files.
  • Deoptimization support (via ReJIT on attach) for .NET Core 3.0 applications.
  • Added symbols to NuGet package.
  • Set more metadata when you upload minidumps.
  • Added an Initialized property to SnapshotCollectorTelemetryProcessor. It's a CancellationToken, which is canceled when the Snapshot Collector is initialized and connected to the service endpoint.
  • Snapshots can now be captured for exceptions in dynamically generated methods. An example is the compiled expression trees generated by Entity Framework queries.

Bug fixes

  • AmbiguousMatchException loading Snapshot Collector due to Status Monitor.
  • GetSnapshotCollector extension method now searches all TelemetrySinks.
  • Don't start the Snapshot Uploader on unsupported platforms.
  • Handle InvalidOperationException when you're deoptimizing dynamic methods (for example, Entity Framework).

1.3.5

  • Added support for sovereign clouds (older versions don't work in sovereign clouds).
  • Adding Snapshot Collector made easier by using AddSnapshotCollector(). For more information, see Enable Snapshot Debugger for .NET apps in Azure App Service.
  • Use the FISMA MD5 setting for verifying blob blocks. This setting avoids the default .NET MD5 crypto algorithm, which is unavailable when the OS is set to FIPS-compliant mode.
  • Ignore .NET Framework frames when deoptimizing function calls. Control this behavior with the DeoptimizeIgnoredModules configuration setting.
  • Added the DeoptimizeMethodCount configuration setting that allows deoptimization of more than one function call.

1.3.4

  • Allowed structured instrumentation keys.
  • Increased Snapshot Uploader robustness. Continue startup even if old uploader logs can't be moved.
  • Reenabled reporting more telemetry when SnapshotUploader.exe exits immediately (was disabled in 1.3.3).
  • Simplified internal telemetry.
  • Experimental feature: Snappoint collection plans: Add snapshotOnFirstOccurence. For more information, see this GitHub article.

1.3.3

Fixed bug that was causing SnapshotUploader.exe to stop responding and not upload snapshots for .NET Core apps.

1.3.2

  • Experimental feature: Snappoint collection plans. For more information, see this GitHub article.
  • SnapshotUploader.exe exits when the runtime unloads the AppDomain from which SnapshotCollector is loaded, instead of waiting for the process to exit. This action improves the collector reliability when hosted in IIS.
  • Added configuration to allow multiple SnapshotCollector instances that are using the same instrumentation key to share the same SnapshotUploader process: ShareUploaderProcess (defaults to true).
  • Reported more telemetry when SnapshotUploader.exe exits immediately.
  • Reduced the number of support files SnapshotUploader.exe needs to write to disk.

1.3.1

  • Removed support for collecting snapshots with the RtlCloneUserProcess API and only support PssCaptureSnapshots API.
  • Increased the default limit on how many snapshots can be captured in 10 minutes from one to three.
  • Allow SnapshotUploader.exe to negotiate TLS 1.1 and 1.2.
  • Reported more telemetry when SnapshotUploader logs a warning or an error.
  • Stop taking snapshots when the back-end service reports the daily quota was reached (50 snapshots per day).
  • Added extra check in SnapshotUploader.exe to not allow two instances to run in the same time.

1.3.0

Changes

  • For applications that target .NET Framework, Snapshot Collector now depends on Microsoft.ApplicationInsights version 2.3.0 or later. It used to be 2.2.0 or later. We believe this change won't be an issue for most applications. Let us know if this change prevents you from using the latest Snapshot Collector.
  • Use exponential back-off delays in the Snapshot Uploader when retrying failed uploads.
  • Use ServerTelemetryChannel (if available) for more reliable reporting of telemetry.
  • Use SdkInternalOperationsMonitor on the initial connection to the Snapshot Debugger service so that dependency tracking ignores it.
  • Improved telemetry around initial connection to Snapshot Debugger.
  • Report more telemetry for the:
    • App Service version.
    • Azure compute instances.
    • Containers.
    • Azure Functions app.

Bug fixes

  • When the problem counter reset interval is set to 24 days, interpret that as 24 hours.
  • Fixed a bug where the Snapshot Uploader would stop processing new snapshots if there was an exception while disposing a snapshot.

1.2.3

Fixed strong-name signing with Snapshot Uploader binaries.

1.2.2

Changes

  • The files needed for SnapshotUploader(64).exe are now embedded as resources in the main DLL. That means the SnapshotCollectorFiles folder is no longer created, which simplifies build and deployment and reduces clutter in Solution Explorer. Take care when you upgrade to review the changes in your .csproj file. The Microsoft.ApplicationInsights.SnapshotCollector.targets file is no longer needed.
  • Telemetry is logged to your Application Insights resource even if ProvideAnonymousTelemetry is set to false. This change is so that we can implement a health check feature in the Azure portal. ProvideAnonymousTelemetry affects only the telemetry sent to Microsoft for product support and improvement.
  • When TempFolder or ShadowCopyFolder are redirected to environment variables, keep the collector idle until those environment variables are set.
  • For applications that connect to the internet via a proxy server, Snapshot Collector now autodetects any proxy settings and passes them on to SnapshotUploader.exe.
  • Lower the priority of the SnapshotUploader process (where possible). This priority can be overridden via the IsLowPrioirtySnapshotUploader option.
  • Added a GetSnapshotCollector extension method on TelemetryConfiguration for scenarios where you want to configure the Snapshot Collector programmatically.
  • Set the Application Insights SDK version (instead of the application version) in customer-facing telemetry.
  • Send the first heartbeat event after two minutes.

Bug fixes

  • Fixed NullReferenceException when exceptions have null or immutable Data dictionaries.
  • In the uploader, retry PDB matching a few times if we get a sharing violation.
  • Fix duplicate telemetry when more than one thread calls into the telemetry pipeline at startup.

1.2.1

Changes

  • XML Doc comment files are now included in the NuGet package.
  • Added an ExcludeFromSnapshotting extension method on System.Exception for scenarios where you know you have a noisy exception and want to avoid creating snapshots for it.
  • Added an IsEnabledWhenProfiling configuration property that defaults to true. This is a change from previous versions where snapshot creation was temporarily disabled if the Application Insights Profiler was performing a detailed collection. The old behavior can be recovered by setting this property to false.

Bug fixes

  • Sign SnapshotUploader64.exe properly.
  • Protect against double-initialization of the telemetry processor.
  • Prevent double logging of telemetry in apps with multiple pipelines.
  • Fixed a bug with the expiration time of a collection plan, which could prevent snapshots after 24 hours.

1.2.0

The biggest change in this version (hence the move to a new minor version number) is a rewrite of the snapshot creation and handling pipeline. In previous versions, this functionality was implemented in native code (ProductionBreakpoints.dll* and SnapshotHolder.exe*). The new implementation is all managed code with P/Invokes.

For this first version using the new pipeline, we haven't strayed far from the original behavior. The new implementation allows for better error reporting and sets us up for future improvements.

Other changes in this version

  • MinidumpUploader.exe has been renamed to SnapshotUploader.exe (or SnapshotUploader64.exe).
  • Added timing telemetry to DeOptimize/ReOptimize requests.
  • Added gzip compression for minidump uploads.
  • Fixed a problem where PDBs were locked preventing site upgrade.
  • Log the original folder name (SnapshotCollectorFiles) when shadow-copying.
  • Adjusted memory limits for 64-bit processes to prevent site restarts due to OOM.
  • Fixed an issue where snapshots were still collected even after disabling.
  • Log heartbeat events to customer's AI resource.
  • Improved snapshot speed by removing "Source" from the problem ID.

1.1.2

Changes

  • Augmented usage telemetry.
  • Detect and report .NET version and OS.
  • Detect and report more Azure environments (Azure Cloud Services, Azure Service Fabric).
  • Record and report exception metrics (number of first-chance exceptions and the number of TrackException calls) in Heartbeat telemetry.

Bug fixes

  • Correct handling of SqlException where the inner exception (Win32Exception) isn't thrown.
  • Trimmed trailing spaces on symbol folders, which caused an incorrect parse of command-line arguments to the MinidumpUploader.
  • Prevented infinite retry of failed connections to the Snapshot Debugger agent's endpoint.

1.1.0

Changes

  • Added host memory protection. This feature reduces the impact on the host machine's memory.
  • Improved the Azure portal snapshot viewing experience.