Physalia is a transactional key- value store, optimized for use in large-scale cloud control planes, which takes advantage of knowledge of transaction patterns and infrastructure design to offer both high availabil- ity and strong consistency to millions of clients. Physalia uses its knowledge of datacenter topology to place data where it is most likely to be available. Instead of being highly available for all keys to all clients, Physalia focuses on being extremely available for only the keys it knows each client needs, from the perspective of that client. This paper describes Physalia in context of Amazon EBS, and some other uses within Amazon Web Services.

Really interesting serverless switch-over story, lots of details and tools used.