Kestrel

Kestrel is the  preferred web server for newer ASP.NET applications
it is an :
- open-source ( GitHub),
- event-driven,
- asynchronous
- I/O based
- web server to host ASP.NET applications
- on any platform

it is used in conjunction with other web servers such as IIS , apache or nginx

Because it is lightweight, Kestrel does not allow you to do SSL termination, URL rewrites, or GZip compression,
It was built to be fast;  six times faster than node.js for static and plain text operations.

install on OpenWRT

https://forum.openwrt.org/t/dotnetcore3-on-openwrt/69435
Follow instructions from this excellent article. https://davidjmclaughlin.com/projects/how-to/2020/03/15/running-.net-core-on-openwrt-and-raspberry-pi-4.html.
Don’t worry about the errors at the end, this thing now runs fine on openwrt 19.

You need to install the packages : libstdcpp6, libintl-full8, icu on openwrt

To run dotnet apps on openwrt, there are 3 different scenarios:
1. Cross build the app on your host/dev machine and copy the executable to openwrt to run it.
2. install the dotnet runtime on the openwrt router. In this case you only need to copy the assembly dll to openwrt to run it.
Note both 1 and 2 requires the router uses arm64 and x64.
3. You can also install the runtime+sdk if the router uses x64. In this case you can do the development on the openwrt router.

added additional comments on the test app:
GitLab OpenWrt test dotnet program ($1953328) · Snippets · Snippets 40