title: Can AWS ELB sticky sessions be used for backend requests?
body: <p>I currently have my web application hosted on AWS, and I use two ELB instances, one to load balance the frontend requests to the app servers, and a second to load balance the backend requests FROM the app servers TO the API servers, like so (sorry for the crappy ascii diagram):</p>
  
  <pre><code>           /--&gt;APP1--\    /--&gt;API1
  User--&gt;ELB1           ELB2
             \--&gt;APP2--/    \--&gt;API2
  </code></pre>
  
  <p>In other words, the API requests that the APP servers make are load balanced evenly across the two backend API servers.</p>
  
  <p>But, because I'm caching responses on the API servers, and use a cache invalidation mechanism which is NOT shared between the API servers, I'd like for a user's session to be stuck to one backend API server. </p>
  
  <p>I already have the user's session stuck to one APP server, using the normal ELB load balancer-generated cookie stickiness, but is there any way to get the backend ELB stuck to a session? Of course, those requests are not coming from a browser, so there's nothing to manage cookies, and it seems that ELB's can only manage stickiness with cookies. Can I emulate the necessary cookies my backend requests?</p>