Hi @Ryan Tay ,
There shouldn't be any perceivable downtime during scale up operations; however, you can always refer to these best practices to ensure you're scaling in an optimum fashion. The operation should take all of few seconds to obtain the additional/upgraded scale units and for those units to start receiving traffic.
One thing to note though. If your application is session based however, there will be disconnect between your clients and your app since the AAR cookie is based on the instance. If you fall in this scenario, it would be best to plan a window for your upscale operation
