Does anyone know the exact details of what Redis is using to prevent something like this?

I think they have a clause saying you can't provide Redis as a Service without paying royalty.

It does feel like we go in circles sometimes in tech, all these license discussions, closed v/s open v/s closed.

I really hope AWS does the decent thing and acknowledges and maybe even donates to the project.

This whole bit reeks of mercenary behaviour. Sure, the license allows it, but AWS still can afford to be a better citizen.