I'm talking about a corporate portfolio of applications, but for my portfolio I can see DynamoDB and Lex as being services that I can't replicate in another cloud. We use DynamoDB for state management. I suppose we could use Redis since that's a service that would be available on more clouds? Or maybe we should abstract ourselves away from state management and create plug-ins for different cloud platforms?

For things like Lex, yeah, that's never going to be cleanly cross-platform. Your application architecture can isolate that technology from the rest of your application so you can cleanly port it if you have to.

Appreciate the nod to 12 factor. Thanks!