title: Elastic beanstalk auto scaling - how long to bring up a new instance
body: <p>I'm trying to decide what metric to use as a trigger for eb auto scaling to fire up a new instance, and what I'm leaning towards atm is response time - so if a user doesn't get a response in say 4 seconds another ec2 instance is fired up.</p>
  
  <p>What I'm struggling to find out, however, is how long it takes on average for eb to bring another instance online. I'm just concerned that if it gets to the point where the existing instances aren't coping with the load, are people going to be refused a connection and/or experience an extremely slow website for several minutes until auto scaling detects the problem and brings another instance online?</p>
  
  <p>If anyone has experience of this with an ecommerce solution I would love to hear what auto scaling configuration you find works to ensure a seamless user experience.</p>