> You can't underscale part of your app with a monolith. Your pipe has to be big enough for all of it.
Not necessarily. I owned one of Amazon’s most traffic-heavy services (3 million TPS). It was a monolith with roughly 20 APIs, all extremely high volume. To keep the monolith simple and be able to scale it up or down independently, the thousands of EC2 instances running it were separated in fleets, which serving a specific use case. Then we could for example scale the website fleet while keeping the payment fleet stable. The only catch is that teams needed to be allowed to call only the APIs representing the use case of that fleet (no calling payment-related APIs on the website fleet). Given the low number of APIs and basic ACL control, it was not a challenge.
Not necessarily. I owned one of Amazon’s most traffic-heavy services (3 million TPS). It was a monolith with roughly 20 APIs, all extremely high volume. To keep the monolith simple and be able to scale it up or down independently, the thousands of EC2 instances running it were separated in fleets, which serving a specific use case. Then we could for example scale the website fleet while keeping the payment fleet stable. The only catch is that teams needed to be allowed to call only the APIs representing the use case of that fleet (no calling payment-related APIs on the website fleet). Given the low number of APIs and basic ACL control, it was not a challenge.