EventSource / Server-Sent Events through Nginx

Question

On server-side using Sinatra with a stream block.

get '/stream', :provides => 'text/event-stream' do
  stream :keep_open do |out|
    connections << out
    out.callback { connections.delete(out) }
  end
end

On client side:

var es = new EventSource('/stream');
es.onmessage = function(e) { $('#chat').append(e.data + "\n") };

When i using app directly, via http://localhost:9292/, everything works perfect. The connection is persistent and all messages are passed to all clients.

However when it goes through Nginx, http://chat.dev, the connection are dropped and a reconnection fires every second or so.

Nginx setup looks ok to me:

upstream chat_dev_upstream {
  server 127.0.0.1:9292;
}

server {
  listen       80;
  server_name  chat.dev;

  location / {
    proxy_pass http://chat_dev_upstream;
    proxy_buffering off;
    proxy_cache off;
    proxy_set_header Host $host;
  }
}

Tried keepalive 1024 in upstream section as well as proxy_set_header Connection keep-alive;in location.

Nothing helps :(

No persistent connections and messages not passed to any clients.

Answer 1

Your Nginx config is correct, you just miss few lines.

Here is a "magic trio" making EventSource working through Nginx:

proxy_set_header Connection '';
proxy_http_version 1.1;
chunked_transfer_encoding off;

Place them into location section and it should work.

You may also need to add

proxy_buffering off;
proxy_cache off;

That's not an official way of doing it.

I ended up with this by "trial and errors" + "googling" :)