My team and I are trying to come up with the best way to implement blue/green for AWS ECS but we can't seem to definitively answer one question about application load balancers.
So far, the method that seems to meet our goals the most is by deploying a blue service and a green service into separate target groups and updating the listener on our application load balancer. However, we have a few longer-running transactions and according to this article:
This method of blue/green does not gracefully drain connections. However, I read a post recently by another AWS engineer that contradicts that, and claims that modifying the listener only affects new incoming connections and therefore does drain gracefully.
Can anyone shed light on what actually happens when I modify the listener for an ELB?