[lukax]

HAProxy allows easier proxying of WebSockets (without having to know all the WebSocket URLs). It also allows proxying TCP traffic without much hassle (in nginx you have to compile/enable stream module - at least in default Ubuntu package). Until long nginx did not allow proxying HTTP requests without caching request body which may be undesired behaviour if you are uploading big files and want the backend to start processing the body as soon as possible.