Summary
This community article applies to Dynatrace OneAgent for Windows /.NET running on Microsoft IIS with deep monitoring enabled. It helps you diagnose and resolve IIS application pool crashes that occur because the application is obfuscated with ConfuserEx or a similar tool, which includes protection that terminates the process when a instrumentation is detected.
Problem
- IIS application pools crash shortly after application startup when OneAgent deep monitoring is enabled.
- Dynatrace OneAgent logs show that assemblies/modules cannot be instrumented
- Example logs line from OneAgent logs -
Module is unsupported (obfuscated or unsupported version). Skipping instrumentation. (AppConfig.dll)
Why this happens
ConfuserEx is a .NET obfuscation tool that includes anti‑debugging and anti‑tampering protections.
When ConfuserEx detects:
- a debugger,
- a profiler,
- or runtime instrumentation (such as Dynatrace OneAgent deep monitoring), it intentionally terminates the process by calling:
Environment.FailFast
This behavior is implemented directly in ConfuserEx, as shown here:
ConfuserEx source (AntiDebug.Safe.cs)
https://github.com/yck1509/ConfuserEx/blob/v1.0.0/Confuser.Runtime/AntiDebug.Safe.cs#L13
Microsoft documentation- Environment.FailFast MethodIt's important to note that Applications using ConfuserEx are known to be incompatible with the Dynatrace OneAgent, and crashes in such scenarios are expected. As a result, using ConfuserEx with the Dynatrace .NET agent is not supported.
Troubleshooting steps
- Confirm with the application Developers whether ConfuserEx or any other obfuscator is used.
- Check for OneAgent logs with entry -
Module is unsupported (obfuscated or unsupported version). Skipping instrumentation. (AppConfig.dll) - Check the windows event logs. You may search for following entry in the Windows Events.
Resolution
Option 1: Disable deep monitoring for the affected process group.
Option 2: Rebuild the application without ConfuserEx obfuscation.
Option 2: Rebuild the application without ConfuserEx obfuscation.
Note:
In some scenarios the obfuscation tool may not crash the process but might lead to missing code-level data in trace and break some trace correlation.
What's next
If this article did not help, please open a support ticket, mention that this article was used and provide the following in the ticket:
- OneAgent Support Archive from the affected host.
