HWLoadbalancerCheckErrors

Some Hardware Load-balancers such Cisco's CSS and BigIP Products test the readiness of the backend Machines with SYN-ACK-RST.

This behavior causes a 400 error in NGINX.

With the GEO Module and the if-Statement you can omit these entries:

Http {

  geo  $lb  {
    default      0;
    10.1.1.1/32  1;   # LB IPs

    10.1.1.2/32  1;
  }

  # ...

  server {

    # ...
    Access_log   /path/to/log;
    error_page 400 /400;

    location = /400 {

      if ($lb) {
        access_log  off;
      }
      return 400;
    }

  }
}