October 21, 2020

Proxying Websockets With Nginx

WebSockets use HTTP/1.1 headers to do a handshake before establishing the binary connection. The client will set Upgrade: websocket and Connection: upgrade header values. Nginx’s proxy_pass directive by default does not forward these headers as there are considered hop-by-hop headers.

Nginx also only uses HTTP/1.0 by default for outbound requests. Therefore, we must override the HTTP version and set header values to make WebSockets work.

server {
  listen 8080;
  server_name backend;
  location / {
    # Upgrade from http/1.0 which is the default.
    proxy_http_version 1.1;

    # If the headers are set then proxy them.
    # Nginx will drop any headers with empty values by default.
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection $http_connection;

    # Always a good idea to pass through real client IP.
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;

    proxy_pass http://backend:8080;

See http://nginx.org/en/docs/http/websocket.html