Task Statement 2.2: Design highly available and/or fault-tolerant architectures.

📘AWS Certified Solutions Architect – (SAA-C03)

1. What Are Purpose-Built AWS Services?

Purpose-built services are AWS services designed to solve a specific type of problem very efficiently.

Instead of building everything manually (like managing servers, databases, queues), AWS provides ready-made services that are:

Highly available (HA)
Fault-tolerant (FT)
Scalable
Managed (less operational work)

Key Idea for Exam:

Use the right tool for the job instead of building everything on EC2.

2. Why Use Purpose-Built Services?

Using these services helps you:

1. Improve Availability

Built-in replication
Multi-AZ support
Automatic failover

2. Improve Fault Tolerance

Service continues even if a component fails
No single point of failure

3. Reduce Operational Effort

No server management
No patching or maintenance

4. Scale Automatically

Handle sudden traffic increases

3. Categories of Purpose-Built AWS Services

For the exam, you must understand which service to use for which workload.

3.1 Compute Services

1. Amazon EC2

Virtual servers
Full control
Needs manual HA setup

👉 Use when:

Custom applications
Legacy systems

2. AWS Lambda

Serverless compute
Runs code automatically

👉 Use when:

Event-driven workloads
No server management required

HA/FT Benefits:

Auto scaling
Multi-AZ by default

3. Amazon ECS / EKS

Container management

👉 Use when:

Microservices
Containerized applications

3.2 Storage Services

1. Amazon S3

Object storage

👉 Use when:

Static files
Backups
Logs

HA/FT Features:

99.999999999% durability
Multi-AZ storage

2. Amazon EFS

Shared file storage

👉 Use when:

Multiple EC2 instances need same files

3. Amazon FSx

Managed file systems (Windows, Lustre)

3.3 Database Services (Very Important for Exam)

1. Amazon RDS

Managed relational database

👉 Use when:

Structured data
SQL queries

HA Features:

Multi-AZ deployments
Automated backups
Read replicas

2. Amazon DynamoDB

NoSQL database

👉 Use when:

High performance at any scale

HA Features:

Serverless
Multi-AZ automatically

3. Amazon Aurora

High-performance relational DB

👉 Use when:

Need better performance than RDS

HA Features:

Auto-replication across AZs
Fast failover

3.4 Networking & Content Delivery

1. Elastic Load Balancer (ELB)

Distributes traffic

👉 Use when:

Multiple application servers

HA Benefit:

Removes single point of failure

2. Amazon CloudFront

Content Delivery Network (CDN)

👉 Use when:

Global content delivery

3. Amazon Route 53

DNS service

👉 Use when:

Traffic routing

HA Features:

Health checks
Failover routing

3.5 Messaging & Integration Services

1. Amazon SQS

Message queue

👉 Use when:

Decoupling applications

HA Features:

Highly durable
Prevents system failure due to overload

2. Amazon SNS

Notification service

👉 Use when:

Sending alerts/messages

3. Amazon EventBridge

Event routing

👉 Use when:

Event-driven architectures

3.6 Caching Services

Amazon ElastiCache

In-memory cache

👉 Use when:

Reduce database load
Improve performance

4. Key Exam Concept: Choose Managed Over Self-Managed

Example Scenario:

Instead of:

Running database on EC2 ❌

Use:

RDS / DynamoDB ✅

Why?

Built-in HA
Automatic backups
Failover handled by AWS

5. Common Design Patterns Using Purpose-Built Services

5.1 Decoupled Architecture

Use:

SQS between components

Benefit:

If one component fails → system continues

5.2 Event-Driven Architecture

Use:

Lambda + EventBridge

Benefit:

Automatic processing
No server management

5.3 Highly Available Web App

Use:

EC2 + ELB + Auto Scaling + RDS Multi-AZ

5.4 Serverless Architecture

Use:

API Gateway + Lambda + DynamoDB

6. Important Exam Tips

1. Prefer Serverless First

Lambda
DynamoDB
S3

2. Prefer Managed Services Over EC2

Less operational effort
Better reliability

3. Use Multi-AZ Services

RDS Multi-AZ
S3 (automatic)
DynamoDB (automatic)

4. Decouple Components

Use SQS, SNS

5. Avoid Single Point of Failure

Use load balancers
Use replication

7. Comparison Table (Very Important for Exam)

Requirement	Best Service
File storage	S3
Shared file system	EFS
Relational DB	RDS / Aurora
NoSQL DB	DynamoDB
Event processing	Lambda
Queue system	SQS
Notifications	SNS
Global content	CloudFront
DNS routing	Route 53
Caching	ElastiCache

8. Common Exam Questions (What AWS Expects You to Choose)

If question says:

“Fully managed” → Avoid EC2
“Automatic scaling” → Lambda / DynamoDB
“High availability with minimal effort” → Managed service
“Decouple application” → SQS
“Event-driven” → Lambda + EventBridge

9. Summary (Must Remember)

Purpose-built services are specialized AWS tools
They provide:
- High availability
- Fault tolerance
- Scalability
Always:
- Choose managed over self-managed
- Avoid single points of failure
- Use decoupling (SQS, SNS)
- Use serverless where possible