We decided to upgrade our website Asp.net core code from .net5 to .net6, we simply set the 'target framework' of the web application to.net6 from .net5. There were no compilation errors, we gave it a test in our development environment and all seemed well. There were no code changes at all made, and previously the .net5 application has been running for many months without issue (and before that .net framework 4.8).
When we deployed our app to our live production environment, within a few minutes we noticed a slowdown of external calls (calls to https endpoints, often REST-like), we log any calls that take more than 5 seconds, over the space of a few minutes all calls went from slow to timing out (20 seconds).
We are using System.Net.WebClient for all of our calls, which I understand is now obsolete in .net6, however, I would not expect this to suddenly change behavior, and even so, we attempted to change to HttpClient, the recommended approach, with the same results.
I feel like I must be missing something really fundamental, we just upgraded the target framework and redeployed and now all calls made by WebClient eventually timeout. It feels like a "running out of resources" issue, in code, due to the slow down then timeout, but I am at a loss to explain what is going on here.
To be clear, we are not doing anything special, just calling about 3 external services via WebClient for each user, and we have maybe 100 users a minute at peak, previously, there have been no timeouts.
Any pointers on what might be causing the timeouts would be greatly appreciated.
I guess time will tell if this is the answer, but we changed all of our calls to use DownloadStringTaskAsync and UploadStringTaskAsync, i.e. all calls from blocking to async await, and after 24hrs, we have not seen the same behaviour in our live environment under full load.
Why a web app using .net 5 core would not have these issues but .net 6 would, is hard to understand. For context, we are not under crazy high load, we are talking a peak of perhaps 150 users per minute, but that is what we are seeing.
Perhaps it was something specific to our set up, but I am writing this to save someone else the pain of trying to debug this issue in the future.