Is the most recent AWSALB cookie required? (AWS ELB Application Load Balancer) : <h2>Observations</h2>

<p>When using an Amazon ELB <em>Application Load Balancer</em> and working with <a href="https://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-target-groups.html#sticky-sessions" rel="noreferrer">Sticky Sessions</a> the load balancer inserts a cookie named <code>AWSALB</code> in the first request. To let the next request stick to the same target node (EC2 instance) the cookie should be included in that request. When doing so, it seems that the load balancer inserts a different cookie value in the response to the 2nd request. When including this new cookie value on the 3rd request, we get yet a new cookie value in the response. And so forth…</p>

<p>(This is different from how <a href="https://docs.aws.amazon.com/elasticloadbalancing/latest/classic/elb-sticky-sessions.html" rel="noreferrer">Sticky Sessions works with the Classic Load Balancer</a> where the cookie is named <code>AWSELB</code> and retains its value until discarded by the client or the load balancer.)</p>

<p>The reason the <code>AWSALB</code> cookie changes value all the time seems to be (as stated by the <a href="https://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-target-groups.html#sticky-sessions" rel="noreferrer">docs</a>):</p>

<blockquote>
  <p>The name of the cookie is AWSALB. The contents of these cookies are encrypted using a rotating key. You cannot decrypt or modify load balancer-generated cookies.</p>
</blockquote>

<p>So even though the contents of the cookie might be the same, we cannot tell.</p>

<h2>Question</h2>

<p>The question is whether a request to the load balancer must <em>always</em> include the most recently received value of the <code>AWSALB</code> cookie or if it ok to send some previously received value (from the same sticky session, of course).</p>

<p>If this is a requirement the AWS ELB Application Load Balancer would not be able to serve a client that performs multiple parallel requests (after having received the first <code>AWSALB</code> cookie) but only clients that performs all requests in a sequential fashion (one at a time).</p>

<p>Can anybody shed some light on this?</p>
