By mining your nginx log with LOGSTASH (you'll need ELASTICSEARCH for database and KIBANA for see information)

forwarding.conf

# into Nginx server
# how install: https://github.com/elastic/logstash-forwarder#building-it
#  git clone git://github.com/elasticsearch/logstash-forwarder.git
#  cd logstash-forwarder
#  go build // it's necessary to install go interpreter
# vi forwarding.conf
# cmd to start service> ./logstash-forwarder -config forwarding.conf 

#### ATTENTION when you generate the certificate
# the name on CN flag into comand openssl will be the same of servers configuration into file
# exemple:
# cmd: openssl req -x509 -subj '/CN=logstashserver.mycompany.com:5000/' -nodes -newkey rsa:2048 -keyout logstash-forwarder.key -out logstash-forwarder.crt
# see more: https://github.com/elastic/logstash-forwarder#important-tlsssl-certificate-notes
{
  "network": {
    "servers": [ "logstashserver.mycompany.com:5000" ],

    "ssl certificate": "/usr/local/etc/logstash-forwarder/logstash-forwarder.crt",
    "ssl key": "/usr/local/etc/logstash-forwarder/logstash-forwarder.key",
    "ssl ca": "/usr/local/etc/logstash-forwarder/logstash-forwarder.crt",

    "timeout": 15
  },
  "files": [
    {
      "paths": ["/usr/local/nginx/logs/access.log"],
      "fields": { "type": "nginx-access" }
    }
  ]
}

logstash.conf

# On Logstashserver
#wget -O https://download.elasticsearch.org/logstash/logstash/logstash-1.4.2.tar.gz
#tar zxvf logstash-1.4.2.tar.gz
#vi logstash-1.4.2/logstash.conf
input {
  # * You'll need logstash-forwarder for use lumberjack in another computer - to centralize your logs in a server logstash
  #        it's necessary start a service to send info log
  #        cmd: ./logstash-forwarder -config forwarding.conf 
  lumberjack {
    host => "localhost"
    # The port to listen on
    port => 5000

    # The paths to your ssl cert and key
    ssl_certificate => "/etc/pki/tls/certs/logstash-forwarder.crt"
    ssl_key         => "/etc/pki/tls/private/logstash-forwarder.key"

    # Set this to whatever you want.
    type => "nginx-access"
  }
}
filter {
  # see nginx-access
  if [type] == "nginx-access" {
    grok {
      match => { "message" => "%{NGINXACCESS}" }
    }
  }
}
output {
  elasticsearch {
    cluster => "logstash-dev"
    protocol => http
    node_name => "logstash"
  }
  stdout {}
}

nginx

# On Logstashserver
# vi ./logstash-1.4.2/patterns/nginx
NGUSERNAME [a-zA-Z\.\@\-\+_%]+
NGUSER %{NGUSERNAME}
NGINXACCESS %{IPORHOST:clientip} %{NGUSER:ident} %{NGUSER:auth} \[%{HTTPDATE:timestamp}\] "%{WORD:verb} %{URIPATHPARAM:request} HTTP/%{NUMBER:httpversion}" %{NUMBER:response} (?:%{NUMBER:bytes}|-) (?:"(?:%{URI:referrer}|-)"|%{QS:referrer}) %{QS:agent}

start two services:

On logstashserver

$./logstash-1.4.2/bin/logstash agent -f logstash.conf -w 10 &

On nginx server

LIVINGSTONE:/usr/local/etc/logstash-forwarder/logstash-forwarder -config forwarding.conf

LIVINGSTONE:/usr/local/etc/logstash-forwarder
LIVINGSTONE:/usr/local/go/