Cloud Service Models on AWS (IaaS, PaaS, SaaS)

Cloud services are commonly categorised into three models — Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS). Each model represents a different level of abstraction and determines what you manage versus what AWS manages for you.

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The Service Model Spectrum

Think of cloud service models as a spectrum from "you manage everything" to "you manage nothing":

  More Control                                    Less Control
  ◄──────────────────────────────────────────────────────────►

  On-Premises    IaaS          PaaS          SaaS
  ──────────    ──────        ──────        ──────
  You manage    You manage    You manage    You manage
  everything    OS upwards    app & data    nothing

                AWS manages   AWS manages   AWS manages
                hardware      hardware +    everything
                + network     OS + runtime

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The Responsibility Stack

To understand the models clearly, consider the full technology stack:

Layer	On-Premises	IaaS	PaaS	SaaS
Application	You	You	You	Provider
Data	You	You	You	Provider
Runtime	You	You	Provider	Provider
Middleware	You	You	Provider	Provider
Operating System	You	You	Provider	Provider
Virtualisation	You	Provider	Provider	Provider
Servers	You	Provider	Provider	Provider
Storage	You	Provider	Provider	Provider
Networking	You	Provider	Provider	Provider
Physical Security	You	Provider	Provider	Provider

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Infrastructure as a Service (IaaS)

IaaS gives you the fundamental building blocks of cloud IT. You rent virtualised compute, storage, and networking resources and manage everything from the operating system upwards.

Characteristics

• Maximum flexibility and control
• You choose the operating system, install software, configure security
• You are responsible for patching, updates, and maintenance of the OS and applications
• Closest to traditional IT but without owning hardware

AWS IaaS Services

Service	What It Provides
Amazon EC2	Virtual servers (instances) — you choose the OS, instance type, and configure everything
Amazon EBS	Block storage volumes that attach to EC2 instances (like virtual hard drives)
Amazon VPC	Virtual private networks — you define subnets, routing, firewalls
AWS Direct Connect	Dedicated network connection from your premises to AWS
Amazon S3	Object storage (often considered IaaS, though highly managed)

Example: Running a Web Server on EC2

# Launch an EC2 instance with Amazon Linux 2023
aws ec2 run-instances \
  --image-id ami-0c02fb55956c7d316 \
  --instance-type t3.micro \
  --key-name my-key-pair \
  --security-group-ids sg-0123456789abcdef0

# Then YOU:
# 1. SSH into the instance
# 2. Install nginx or Apache
# 3. Deploy your application
# 4. Configure SSL
# 5. Set up monitoring
# 6. Patch the OS regularly

When to Use IaaS

• You need full control over the OS and runtime
• You are migrating existing on-premises applications ("lift and shift")
• Your application has specific OS-level requirements
• You need custom networking configurations

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Platform as a Service (PaaS)

PaaS removes the burden of managing the underlying infrastructure. You provide your application code and configuration; AWS handles the OS, runtime, patching, and scaling.

Characteristics

• Focus on writing code, not managing servers
• Automatic scaling, load balancing, and health monitoring
• Less operational overhead, but less control
• Ideal for developers who want to ship features quickly

AWS PaaS Services