IaaS vs PaaS vs SaaS: What's the Difference?
Understand the differences between IaaS, PaaS, and SaaS cloud service models, with AWS examples like EC2 and Elastic Beanstalk, for your next interview.
Expected Interview Answer
IaaS, PaaS, and SaaS are the three cloud service models, differing by how much of the stack the provider manages versus what the customer manages: IaaS gives raw infrastructure, PaaS gives a managed application platform, and SaaS gives a fully finished application.
In IaaS (e.g., EC2), the provider manages physical hardware, virtualization, and networking, while you manage the operating system, runtime, and application code. In PaaS (e.g., Elastic Beanstalk), the provider additionally manages the OS, runtime, and scaling, so you only deploy application code and configuration. In SaaS (e.g., Gmail, Salesforce), the provider manages the entire stack including the application itself, and you simply consume it as an end user. Moving from IaaS to SaaS trades control for convenience, shifting more operational burden onto the provider.
- IaaS gives maximum control over OS and runtime configuration
- PaaS speeds development by removing infrastructure management
- SaaS requires zero infrastructure or platform maintenance
- Each model lets teams choose the right control-vs-convenience trade-off
- Mixing models lets an org optimize different workloads independently
AI Mentor Explanation
IaaS is like renting an empty cricket ground where you bring your own team, coach, and equipment. PaaS is like renting a ground with pitch, nets, and groundstaff ready, so you just field a team and play. SaaS is like buying a ticket to watch a fully organized match — someone else runs the venue, teams, and umpiring, and you just enjoy the game.
Step-by-Step Explanation
Step 1
IaaS: infrastructure only
Provider manages physical hardware, virtualization, and network; you manage OS, runtime, and app (e.g., EC2).
Step 2
PaaS: managed platform
Provider additionally manages OS, runtime, and scaling; you deploy just app code (e.g., Elastic Beanstalk).
Step 3
SaaS: finished application
Provider manages the entire stack including the application; you consume it as an end user.
Step 4
Trade-off shifts with each model
Moving IaaS to PaaS to SaaS trades customer control for reduced operational burden.
Step 5
Choose per workload
Teams often mix models — IaaS for custom systems, SaaS for commodity functions like email.
What Interviewer Expects
- Correctly maps each model to the layer of the stack the provider manages
- Gives concrete AWS examples for each (EC2, Elastic Beanstalk, a SaaS product)
- Explains the control-versus-convenience trade-off
- Understands responsibility shifts, tying into the shared responsibility model
- Can justify when to choose each model for a given workload
Common Mistakes
- Mixing up which layer PaaS manages versus IaaS
- Claiming SaaS requires you to manage servers
- Treating the three models as mutually exclusive rather than combinable
- Failing to give real AWS service examples for each category
Best Answer (HR Friendly)
“IaaS, PaaS, and SaaS describe how much of the technology a cloud provider manages for you. IaaS gives you raw computing power you configure yourself, PaaS gives a ready-to-use platform for building apps, and SaaS gives a fully working application you just use, like email or a CRM tool.”
Code Example
aws ec2 run-instances --image-id ami-0abcdef1234567890 --instance-type t3.micro
# You SSH in and install your own runtime, dependencies, and appeb init my-app --platform node.js --region us-east-1
eb create my-app-env
eb deploy
# No server management -- Elastic Beanstalk handles provisioning and scalingFollow-up Questions
- Which AWS services fall under IaaS, PaaS, and SaaS respectively?
- How does the shared responsibility model change across IaaS, PaaS, and SaaS?
- When would you choose PaaS over IaaS for a new project?
- Is AWS Lambda considered PaaS, or something else entirely?
- What are the security implications of using more SaaS in an organization?
MCQ Practice
1. In which service model does the provider manage everything up to and including the operating system and runtime?
PaaS manages the OS, runtime, and scaling, leaving the customer to deploy only application code.
2. Which AWS service is a classic example of IaaS?
EC2 provides raw virtual servers, requiring the customer to manage the OS, runtime, and application -- the definition of IaaS.
3. What does the customer manage in a SaaS product like a hosted email service?
In SaaS, the provider manages the entire application stack; the customer only manages their data, settings, and users.
Flash Cards
What does IaaS give you? — Raw virtualized infrastructure (compute, storage, network); you manage OS, runtime, and app.
What does PaaS give you? — A managed platform where OS, runtime, and scaling are handled; you deploy just application code.
What does SaaS give you? — A fully finished application managed entirely by the provider; you just use it as an end user.
Give an AWS example of each model. — IaaS: EC2. PaaS: Elastic Beanstalk. SaaS: a finished hosted application like Amazon Chime.