Use all the defined unicorn processes.

templates/nginx_unicorn.conf.j2

@@ -7,7 +7,7 @@ upstream unicorn {
     # server unix:/tmp/.sock fail_timeout=0;
 
     # for TCP setups, point these to your backend servers
-    {% for i in range(0, unicorn_worker_processes - 1) %}
+    {% for i in range(0, unicorn_worker_processes) %}
     server 127.0.0.1:{{ unicorn_listen_port + i }} fail_timeout=0;
     {% endfor %}
   }