Question
In AWS, for ELBs, what are Sticky sessions (that you can disable/enable at ELB level) and why are they useful?
Answer
When enabled, Sticky sessions ensure all traffic from a user during a session go to same EC2 instance (or Target Group, for ALBs). This is useful if user data is being saves to a file on the EC2 instnaces for example, so for the whole session traffic from that user must go to same EC2 instance.