How to fix Azure App service F1 free tier Web API The SSL connection could not be established & Cannot determine the frame size or a corrupted frame was received

Question

I have migrated a .NET core 3.1 Web API deployed on Azure App services. I migrated it to .NET 8 version and deployed to same Azure App services. We are using the app services plan F1 free tier. Same was used for .NET 3.1 API also, earlier it is used to work outside the network, but after the upgrade it works only inside the corporate network. and doesn't work outside the corporate network. Its returning the Error as "The SSL connection could not be established" "Cannot determine the frame size or a corrupted frame was received.". What could be the reason, and what configurations to be changed on the App services using the F1 free tier only?

The same upgraded API also deployed on other App service TEST, which has the same configuration as DEV and it works there in TEST. All configurations are same for both DEV and TEST.

Answer

Hello,

Welcome to Microsoft Q&A,

.NET 8 may enforce stricter TLS settings compared to .NET Core 3.1, and the App Service may not has configurations affecting external access.

Solution:
1. Verify that the app service supports the TLS version.
  - Azure App Services support TLS 1.2 by default. Ensure no outdated protocols (e.g., TLS 1.0 or 1.1) are in use in your API or external clients.
2. Configure .NET 8 API to explicitly use TLS 1.2 or higher:
```
      ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;
```
3. Check if your corporate network or a firewall is enforcing specific SSL/TLS settings and adjust as needed.

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How to fix Azure App service F1 free tier Web API The SSL connection could not be established & Cannot determine the frame size or a corrupted frame was received

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