On some websites there are the following headers which consist
Via: 1.1 vegur
I've tried to look for it, but I couldn't find it. Is this is generated by Varnish, some kind of reverse proxy or it's something else?
It's a Heroku proxy/load-balancer adding the
See: Vegur at GitHub.
Heroku's proxy library based on a forked Cowboy frontend (Cowboyku). This library handles proxying in Heroku's routing stack.
via header shows proxies and their names. In this case, the client went through a proxy called "vegur" - either its software or the computer name.