nginx.conf

daemon off;

worker_processes 1;

error_log /dev/stdout debug;
pid /tmp/nginx.pid;

events {
    worker_connections 8192;
}

http {
    server_tokens off;

    server {
      listen 8001;
      access_log /dev/stdout;

      location / {
        proxy_pass http://unix:/tmp/puma.socket;
        proxy_set_header Host $http_host;
        proxy_set_header X-Request-Start "${msec}";
        proxy_read_timeout 30s;
        proxy_request_buffering on;
     }
  }
}

puma.rb

app do |env|
  sleep 5

  [
    200,
    {"Content-Type" => "text/plain"},
    [(Time.now.to_f - env["HTTP_X_REQUEST_START"].to_f).to_s]
  ]
end

threads 1, 1
environment 'production'

workers 1

preload_app!

bind 'unix:///tmp/puma.socket'