IaaS, PaaS, SaaS: A Mental Model That Actually Sticks

The textbook explanation of cloud service tiers goes like this: IaaS gives you raw servers, PaaS gives you a runtime, SaaS gives you a finished product. That's not wrong, but it skips the question that actually matters: who owns the headache?

Here's a more useful way to think about it.

The Responsibility Spectrum

Every cloud service tier is a decision about which operational problems you want to outsource and which you want to control. The trade-off is always the same: flexibility versus maintenance burden.

Where the Model Breaks Down

Real-world cloud services rarely fit neatly into one bucket. AWS Lambda is serverless compute (IaaS-like), but it also manages runtimes and auto-scaling (PaaS-like). Vercel deploys your frontend framework automatically (PaaS) but also provides edge functions (closer to IaaS). Cloudflare Workers sit somewhere between IaaS and PaaS depending on how you use them.

The lines don't matter much in practice. What matters is understanding what you're taking responsibility for:

The Migration Path

Most teams I've seen start with IaaS because it's familiar: you're basically running a data center in someone else's building. Over time, they move up the stack:

1. Start with IaaS to maintain control during migration
2. Move stateless services to PaaS to reduce ops load
3. Replace commodity tools (email, document storage, CI) with SaaS

You don't have to pick one tier for everything. A typical modern stack might run the database on IaaS (full control), the API on PaaS (auto-scaling), and use SaaS for email, monitoring, and team communication.

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