aws负载平衡器引脚到一个实例

in my project I have two instances (based on ECS) which run Node.js app. Both of them are the same (just for HA purposes) use cookies and are located behind load balancer. Problem is that instances don't share session between themselves and when I login to first instance and do back action, load balancer sometimes switch me to second instance which doesn't have any session data (cookie generated by first instance) and I need to login again. I know that there is option to force two instances to share session between themselves but this approach require some modification in app code. So instead of it I would like to force my load balancer to hold and use this one instance which he had chosen for first time until the user finished his job and log off (or close the browser). Is it possible? in my project I have two instances (based on EC