title: Understanding AWS ELB Latency
body: <p>I'm keen to understand exactly what the ELB Latency Statistic provided by CloudWatch means.</p>
  <p>According to the docs:</p>
  <ul>
  <li>ELB Latency: &quot;Measures the time elapsed in seconds after the request leaves the load balancer until the response is received.&quot;</li>
  </ul>
  <p><a href="http://docs.aws.amazon.com/ElasticLoadBalancing/latest/DeveloperGuide/US_MonitoringLoadBalancerWithCW.html" rel="nofollow noreferrer">http://docs.aws.amazon.com/ElasticLoadBalancing/latest/DeveloperGuide/US_MonitoringLoadBalancerWithCW.html</a></p>
  <p>What I'm not 100% clear on is whether or not the response gets buffered to the ELB before it gets transferred to the client?</p>
  <p>Does the statement in the docs mean:</p>
  <ul>
  <li>ELB Latency: &quot;Measures the time elapsed in seconds after the request leaves the load balancer until the response is received [by the client].&quot;</li>
  </ul>
  <p>Or:</p>
  <ul>
  <li>ELB Latency: &quot;Measures the time elapsed in seconds after the request leaves the load balancer until the response is received [by the ELB].&quot;</li>
  </ul>
  <p>I want to understand whether or not a poor Maximum Latency CloudWatch metric could be explained by having a significant number of users on  3G connections, or, if it instead indicates an underlying problem with the app servers occasionally responding slowly.</p>