Author here. Happy to answer any questions.
Other than ec2, what AWS services were you using and how did you migrate those? At minimum, I'd guess you were using elb for load balancing, sqs for queues and elastic cache for redis.
For load balancing we have moved to a Route53 (health checks and round-robin) + a group of nginx+haproxy+lua-based frontend boxes.
Everything else was either built in-house or used open-source components and wasn't really tied to EC2 infrastructure.