72 Hours into the migration and we are finally starting to see production issues with performance. Sad thing is, these guys (not AWS) we're working with aren't quick at finding issues. It might be a CPU/memory problem because we ruled out a database issue, so something else must be causing the slowness. Must be an application server issue. The post migration fun has begun.
But otherwise, the migration during the weekend was very successful and we didn't encounter any big issues. AWS said it was one of the most smooth transitions they have ever seen, which was basically in 5 months. Shit ton of more work coming my way.