What the f--k it is?
It's a very simple but quick backend for proxy servers. You can setup redirect to your main domain or just show
HTTP/1.1 404 Not Found with zero memory allocation and very fast response. Also useful when you need to serve many redirects or not found errors but don't want any overheads.
git clone firstname.lastname@example.org:kirillDanshin/llb.git cd llb go build # run in background with default ports # but custom redirect destination ((./llb -redirDest="https://google.com/" &)&)&
Than setup your proxy to send any invalid requests like invalid host etc to this backend.