Request are stucking in AuthenticateRequest State on IIS

Question

We're facing a critical issue with our API server. It's built on C# .NET 4 with a C++ backend. The problem manifests as certain requests hitting the IIS of the backend server some instances, these requests remain stuck in the AuthenticateRequest state, which is at the very beginning of the IIS pipeline's request lifecycle. Most of them become stuck there and eventually time out.

Key points about our setup:

The implementation heavily utilizes asynchronous operations.

There are no database locks causing contention.

CPU load consistently remains at 10-20%, indicating no significant strain.

Our environment runs on Windows Server 2019 with IIS version 10.0.17763.1.

We operate two servers (server 1 and (server 2) connected to a single database, both running the same project. Additionally, we run identical APIs on both servers for synchronization purposes.

However, the issue only occurs on server 1; server 2 functions without problems.

We're open to any advice or ideas for further debugging on IIS, along with any additional information you may need.

Answer 1

AuthenticateRequest is part or the asp.net pipeline. this event handler is typically defined in global.aspx (or its code behind) file. but any HttpModule could subscribe to the event (see web.config for list of HttpModules registered). you need to debug the code (maybe add trace events).