list cloufront ip ranges for nginx real ip module

nginx_config_cloudfront_real_ips.js

var request = require("request");
var fs = require("fs");
var output = "#cloudfront ip ranges\n";
request("https://ip-ranges.amazonaws.com/ip-ranges.json", function(err, res, body) {
    if (err) {
      console.error("error", err);
    }
    var j = JSON.parse(body);
    j.prefixes.forEach(function(item) {
      if (item.service ==='CLOUDFRONT') {
        output += "set_real_ip_from " + item.ip_prefix + ";\n"
      }

    })
    fs.writeFileSync(__dirname + "/etc/cloudfront_ips", output);
    console.log("write cloudfront ips");    
});