Shifting from SOA Software Engineer to Distributed Systems Engineer

I am a generic software engineer right now and work on writing backend services, calling them from the front end and adding some monitoring and metrics to the service. Service Oriented Architecture in short. The services I contribute to already serve millions of customers. But all that is handled for me via AWS. I have used SQS, Dynamo, S3 and Lambda functions and have a good working knowledge of them. I want to shift to a job where I write code that works in a distributed environment. Something like working at Dropbox on a service that does parallel processing and uses distributed computing to serve millions of customers. Another reference would be, ability to design scalable architecture for startups that can handle growth from 50 to 5 million users. (AWS etc. kind of already does that for you. So then what's there to learn?) PS: Please let me know if the question sounds ambiguous/nonsense and I will edit it further for clarification.