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;
}
}