gistfile1.txt

upstream backend {
    server 127.0.0.1:3000;
}

server {
    listen 80;

    access_log /var/log/nginx/yoursite.access.log;
    error_log /var/log/nginx/yoursite.error.log;

    server_name api.yoursite.com

    # prevents 502 bad gateway error
    large_client_header_buffers 8 32k;

    location / {
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header Host $http_host;
        proxy_set_header X-NginX-Proxy true;

        # prevents 502 bad gateway error
        proxy_buffers 8 32k;
        proxy_buffer_size 64k;

        proxy_pass http://backend;
        proxy_redirect off;

        # enables WS support
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
    }
}

I still get randomly 502 errors with this config

I had commented this line
proxy_set_header Connection "upgrade";
uncommented it and it worked. Thank you