aws-elb-util

A few utilities to let an AWS EC2 instance figure out whether it is the only instance (or 'first' instance) on a Load Balancer. The main purpose if to make it easy to ensure that single instances of a worker process can be run in an installation as servers get added and taken down.

npm install aws-elb-util


var awsUtil = require('aws-elb-utils');

Configure through config file, which must include owner_id. AWS accessKeyId and secretAccessKey can be in config file or in environment variables AWS_ACCESS_KEY and AWS_SECRET_ACCESS_KEY.

awsUtil.configure(configFilename);

Determining whether you are running on EC2

awsUtil.onEC2 (function (err, onEC2) {
  ;
});
 

Getting the instance id

awsUtil.getInstanceId (function (err, instanceId) {
  ;
});

Get information about load balancers

awsUtil.getLoadBalancers (configObject, function(err, loadBalancers)) {
  ;
});

See if you are the 'primary' instance

awsUtil.amIFirst(function (err, primary, loadBalancer) {
   // primary is a boolean
   // load balancer is the name of the load balancer 
   //   or 
   // -1 (Running on EC2 but not under a load balancer)
   //   or
   // -2 (Not running on EC2)
 });

Handle changing state

awsUtil.handlePromotionDemotion( 
  function onPromotionToPrimary() {},
  function onDemotionFromPrimary() {}
);