Use appropriate log level for errors

[kheardCB]

In the HttpForwarder, the log level for errors is Information. Can this be changed to Error? This may be an issue in other log messages in other files, but this is the main one I noticed.

https://github.com/microsoft/reverse-proxy/blob/5210218470a00ea5359dfefb71d193aacd60b646/src/ReverseProxy/Forwarder/HttpForwarder.cs#L757

Background:
I am using Serilog for logging and setting the MinimumLevel override for "Microsoft.AspNetCore" and "Yarp.ReverseProxy.Forwarder" to Warning. This accompanied with the "UseSerilogRequestLogging" option allows the service to omit one log line per request. In this setup, any errors are not being logged because they are set as Information, not Error.

I would gladly make the change myself and create a Pull Request, if that would be helpful.

[Tratcher]

The main concern here is that we don't want to log anything at the Error level that is caused by an external entity that you can't do anything about, that floods logs unnecessarily. Errors should be actionable within the current app. Timeouts, disconnects, etc. are all expected within normal proxy operations.

To look at the proxy results and decide which ones you want to react to check here:
https://github.com/microsoft/reverse-proxy/blob/029e731a95c08a77af37700b1ab6ecd99e694d83/docs/docfx/articles/middleware.md#error-handling

https://github.com/microsoft/reverse-proxy/blob/79a7b806688311fd2cca2ca67dc7cc418c7925ab/docs/docfx/articles/direct-forwarding.md#error-handling

[karelz]

Triage:

• Error level should be only for YARP problems that are actionable
• Warning level should be for any unsuccessful proxying, things YARP is able to recover from - e.g. destination going out, client-side problems with network - see list in code.
  • Note: Warn level is turned on by default by templates
• Information/Verbose level should be for all successful log entries.

We'd accept changing this log to Warning.

It is a one-line change in https://github.com/microsoft/reverse-proxy/blob/03a4d6a91b9b65f90e8c616bebc77e1338bec81a/src/ReverseProxy/Forwarder/HttpForwarder.cs#L992-L993
@kheardCB are you interested in submitting a PR for it?

Simple to do, brings value and more sanity. We should do it in 2.x.

[kheardCB]

@karelz Sure, I can submit a PR.

[karelz]

Great, looking forward to it @kheardCB!

Let us know if you hit any roadblocks, we will be happy to help.