Amazon biases towards Systems Oriented Architecture approach that is in the middle ground between monolith and microservices.
Biasing away from lots of small services in favour of larger ones that handle more of the work so that as much as possible you avoid the costs and latency of preparing, transmitting, receiving and processing requests.
I know S3 has changed since I was there nearly a decade ago, so this is outdated. Off the top of my head it used to be about a dozen main services at that time. A request to put an object would only touch a couple of services en route to disk, and similar on retrieval. There were a few services that handled fixity and data durability operations, the software on the storage servers themselves, and then stuff that maintained the mapping between object and storage.
Biasing away from lots of small services in favour of larger ones that handle more of the work so that as much as possible you avoid the costs and latency of preparing, transmitting, receiving and processing requests.
I know S3 has changed since I was there nearly a decade ago, so this is outdated. Off the top of my head it used to be about a dozen main services at that time. A request to put an object would only touch a couple of services en route to disk, and similar on retrieval. There were a few services that handled fixity and data durability operations, the software on the storage servers themselves, and then stuff that maintained the mapping between object and storage.