The question is not which one wins, it is where you draw the isolation boundary. Here is how single and multi-tenant differ on cost, isolation, compliance, and ops, and why most SaaS that scales ends up running both at once.
Silo, pool, or bridge is one of the few architecture choices you cannot cheaply reverse. Here are the three models in plain terms, how they map to a real database, and a decision framework so you pick the one your customers and your margins actually need.
Your AWS bill is not a mystery, you just have not grouped it right. Cost Explorer is free and shows you where every dollar goes in about fifteen minutes. Here is the exact drill-down, which cost view to trust, and the one free alarm to set before you close the tab.
Graviton instances cost up to 20% less than the x86 equivalent for the same work. On managed services it is a setting you flip. On your own compute it is a real migration with real gotchas. Here is which workloads move for free, which take effort, and which cannot move at all.
Aurora can be cheaper than RDS or twice the price, and the deciding line item is the one nobody watches: I/O. Here is how the bill is built, when I/O-Optimized and Serverless v2 actually save money, and the traps that turn a managed database into your biggest surprise.
Both trade a commitment for a discount, but they are not interchangeable. Savings Plans buy flexibility, Reserved Instances buy the deepest rate, and the data tier plays by its own rules. Here is how to pick without locking up capital you will regret.
