IIS Application Pool Recycles sometimes cause high CPU usage if .NET agent is installed

Products

• DX Application Performance Management

Issue/Introduction

When recycling an IIS application pool, after a few recycles, CPU usage becomes extremely high. We can easily recreate the issue: we just have to recycle the same pool a few times.

If we remove the .NET agent, the same never happens, regardless of how many times we repeatedly recycle the app pool. We first noticed this problem by noticing that sometimes some production servers would start hogging the CPU and becoming unresponsive. We then determined this coincides with app pool recycles - not every recycle would do this, but after a few it does occur. We set out to test changes to the systems and determined that .NET agent installation was one change on the system. By manually recycling an app pool, we were able to successfully reproduce the issue. Uninstalling the .NET agent, completely removes the issue.

Environment

OS: Windows Server 2022 Standard, Version    21H2, OS build    20348.2762

IIS: 10.0.20348.1

.NET Agent: Agent Release 24.10.1.5 (Build 990005)

Resolution

Our Development team is planning to include a fix in an upcoming release 25.2.2.  Tentative release date is end of May / beginning of June.