[kovidgoyal]

Why have you got both proxy_pass and proxy_redirect? You cannot acces it both as a top level and under /calibre -- that makes no sense. Pick one, for example, if you want it under /calibre

location /calibre
{
proxy_pass http://localhost:8080/calibre;
}

And run the calibre server with

calibre-server --url-prefix /calibre

or if you want to devote a whole virtual host to it

server http://whatever
location / {
proxy_pass http://localhost:8080;
}

and run calibre without --url-prefix