IaaS, PaaS and serverless are three levels of abstraction for running an application in the cloud, differing mainly in how much infrastructure management you take on versus hand off to the provider. IaaS gives raw virtual machines you configure yourself; PaaS handles the operating system and runtime, leaving you to manage just your application; serverless removes server management entirely, running your code only in response to specific triggers and billing per execution.
What Each Model Actually Means
IaaS (Infrastructure as a Service). Think AWS EC2 or Google Compute Engine, gives you virtual machines you configure from the operating system up. Maximum control, maximum responsibility: you handle OS patching, scaling logic, and security configuration yourself.
PaaS (Platform as a Service), Heroku, or App Engine, handles the operating system, runtime and often scaling automatically, letting you deploy application code without managing servers directly. Less control than IaaS, significantly less operational overhead.
Serverless, AWS Lambda, Vercel Functions, takes abstraction furthest: your code runs only when triggered by an event, and you’re billed per execution rather than for continuously running infrastructure. No server management at all, but functions face execution time limits and a “cold start” delay on infrequently used code.
What to Check Before You Buy
- Actual control needed. Custom networking, specific OS-level configuration, or unusual runtime requirements push toward IaaS; standard web application patterns fit PaaS or serverless fine.
- Traffic pattern. Serverless billing suits spiky, unpredictable traffic well; PaaS or IaaS with reserved capacity suits steady, predictable load more cost-effectively.
- Cold start tolerance. Serverless functions that run infrequently face startup latency, a real consideration for latency-sensitive applications.
- Team DevOps capacity. IaaS requires real infrastructure expertise on the team; PaaS and serverless reduce that requirement significantly.
- Vendor lock-in. Serverless functions are often tightly coupled to a specific provider’s event and execution model, making migration between providers harder than with IaaS.
Which Fits Your Project?
A steady-traffic web application with a small team and no unusual infrastructure needs fits PaaS well, deploy and let the platform handle the operational layer. A spiky-traffic API, a background job triggered occasionally, or event-driven processing fits serverless’s per-execution billing model, provided cold-start latency isn’t a problem for the use case. A project with specific compliance, networking, or custom runtime requirements that PaaS and serverless can’t accommodate needs IaaS’s full control, along with the team capacity to manage it.
Frequently Asked Questions
What’s the main difference between PaaS and serverless?
PaaS runs your application continuously on managed infrastructure you don’t configure directly; serverless runs your code only in response to specific triggers, billing per execution rather than for continuous uptime.
Is serverless always cheaper than PaaS or IaaS?
Not always, serverless is typically cheaper for spiky or low, unpredictable traffic, but can cost more than a reserved PaaS or IaaS instance under steady, high-volume traffic.
What is a cold start in serverless computing?
A startup delay that occurs when a serverless function hasn’t run recently and needs to initialize before executing, which can add noticeable latency for infrequently triggered functions.
Do I need DevOps expertise to use IaaS?
Yes, meaningfully more than for PaaS or serverless, IaaS requires configuring and maintaining the operating system, security patching, and scaling logic yourself.
Can I mix IaaS, PaaS and serverless in the same project?
Yes, and many real applications do, using serverless for event-driven background tasks while running the core application on PaaS or IaaS, matching each component to its actual traffic and control needs.
Key Takeaways
- IaaS gives maximum control at maximum operational responsibility; serverless removes server management entirely at the cost of execution limits and cold starts.
- PaaS sits in between, handling the runtime while you focus on application code.
- Serverless billing suits spiky traffic; steady high-volume load often costs less on reserved PaaS or IaaS capacity.
- Serverless functions are often tightly coupled to one provider’s model, raising migration difficulty later.
- Real applications commonly mix all three models, matching each component to its actual needs.
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