nginx proxy_pass 404 error, don't understand why

Question

I am trying to pass off all calls to /api to my webservice but I keep getting 404s with the following config. Calls to / return index.html as expected. Does anyone know why?

Answer 1

By some reason proxy_pass in Nginx cuts header "Host" before passing to upstream, and request catches by default server, and even proxy_header_pass doesn't helps, so I've to explicitly set it:

location / {
    proxy_set_header Host $host;
    proxy_pass  http://backend;
}