AWS Interview Questions and Answers

Top AWS Interview Questions and Answers for beginners and experienced developers. Covers EC2, S3, Lambda, VPC, IAM, API Gateway, CloudWatch, DynamoDB and more.

Module 1: AWS Interview Questions – Core Concepts

✅ 1. What is AWS?

Answer:

Amazon Web Services (AWS) is a cloud computing platform provided by Amazon.

It provides:

servers
storage
databases
networking
monitoring
security
messaging services

using the internet.

Instead of managing physical servers,
companies use AWS cloud infrastructure.

Real-Time Example

Instead of buying servers manually:

deploy Spring Boot applications on AWS
scale automatically
pay only for usage

Key Benefits

✅ No physical server maintenance
✅ Scalable infrastructure
✅ High availability
✅ Global access
✅ Faster deployments

✅ 2. What are the Benefits of AWS?

Answer:

AWS provides:

scalability
flexibility
reliability
security
cost optimization

Main Benefits

1️⃣ Scalability

Increase/decrease servers automatically.

Example:

festival traffic
sale traffic
high API load

2️⃣ Pay-As-You-Go

Pay only for resources used.

No huge upfront investment.

3️⃣ High Availability

Applications can run across:

multiple regions
multiple availability zones

Improves fault tolerance.

4️⃣ Security

AWS provides:

IAM
encryption
security groups
monitoring

5️⃣ Faster Deployment

Infrastructure setup becomes quick.

Deploy applications within minutes.

✅ 3. What is EC2?

Answer:

Amazon EC2 (Elastic Compute Cloud) is a virtual server in AWS cloud.

Used to:

host applications
deploy microservices
run backend APIs

How We Use EC2

Deploy Spring Boot JARs
Configure Linux + Java
Setup environment variables
Configure security groups
Attach load balancer

Real-Time Example

Claims service deployed on:

EC2 instances

Application runs using:

java -jar claims-service.jar

EC2 Benefits

✅ Flexible
✅ Scalable
✅ Easy deployment
✅ Full server control

✅ 4. What is S3?

Answer:

Amazon S3 (Simple Storage Service) is an object storage service.

Used to store:

documents
images
backups
logs
videos
PDFs

Real-Time Example

Claims application:

upload claim documents
store files in S3
save S3 URL in database

Common Use Cases

✅ File storage
✅ Static website hosting
✅ Backups
✅ Log storage

S3 Advantages

✅ Highly scalable
✅ Durable
✅ Secure
✅ Low cost

✅ 5. What is RDS?

Answer:

Amazon RDS (Relational Database Service) is a managed relational database service.

Supports:

MySQL
PostgreSQL
Oracle
SQL Server

Features

✅ Automated backups
✅ High availability
✅ Read replicas
✅ Managed maintenance

Real-Time Example

Policy application stores:

customer data
policy details
transactions

inside RDS database.

✅ 6. What is DynamoDB?

Answer:

Amazon DynamoDB is a fully managed NoSQL database service.

Stores data using:

key-value
document-based structure

Features

✅ Highly scalable
✅ Serverless
✅ Low latency
✅ Automatic scaling

Real-Time Understanding

DynamoDB is similar to:

MongoDB

But:
AWS fully manages infrastructure.

Common Use Cases

session management
shopping carts
real-time applications
high-volume systems

✅ 7. Difference Between RDS and DynamoDB?

Answer:

Feature	RDS	DynamoDB
Type	Relational DB	NoSQL DB
Schema	Fixed	Flexible
Query Language	SQL	Key-based
Scaling	Vertical	Automatic
Relationships	Supported	Limited
Best For	Transactions	High-scale systems

Real Interview Understanding

Use RDS when:

relationships exist
joins needed
transactions important

Example:

banking
policy systems
order systems

Use DynamoDB when:

massive scalability needed
flexible schema needed
ultra-fast access required

Example:

session storage
gaming
real-time tracking

🎯 Best Final Interview Answer

RDS is relational and suitable for structured transactional systems.

DynamoDB is NoSQL and better for highly scalable distributed systems.

RDS vs DynamoDB Comparison

High-level comparison between relational and NoSQL AWS databases.

feature	rdsScore	dynamoScore
Structured Schema	10	4
Flexible Schema	4	10
SQL Support	10	2
Auto Scalability	6	10
Complex Joins	10	1
High Throughput	7	10

Module 2: AWS Compute Services 🚀

✅ 1. What is EC2?

Answer:

Amazon EC2 (Elastic Compute Cloud) is a virtual server in AWS cloud.

Used to:

deploy applications
host Spring Boot microservices
run backend APIs

How We Use EC2

Launch Linux server
Install Java
Upload Spring Boot JAR
Configure environment variables
Run application

Example

java -jar claims-service.jar

Real-Time Example

Claims service deployed on:

EC2 instances

Load balancer distributes traffic across multiple EC2 servers.

EC2 Advantages

✅ Flexible
✅ Scalable
✅ Full server control
✅ Easy deployment

Important Interview Point 🎯

EC2 gives:

Infrastructure as a Service (IaaS)

You manage:

OS
application
runtime
configurations

✅ 2. What is AWS Lambda?

Answer:

AWS Lambda is a serverless compute service.

Runs code:

without managing servers
based on events

Key Features

✅ No server management
✅ Auto scaling
✅ Pay per execution
✅ Event-driven execution

Real-Time Example

When:

claim document uploaded to S3

Lambda automatically:

validates file
resizes image
processes document

Common Lambda Triggers

S3 upload
API Gateway request
SQS message
CloudWatch event

Important Interview Point 🎯

Lambda best suited for:

short-running tasks
event-driven systems
lightweight processing

NOT ideal for:

long-running applications

EC2 vs Lambda

Feature	EC2	Lambda
Server Management	Required	Not Required
Scaling	Manual/Auto Scaling	Automatic
Billing	Per running server	Per execution
Best For	Long-running apps	Event-driven tasks

✅ 3. What is ECS?

Answer:

Amazon ECS (Elastic Container Service) is a container orchestration service.

Used to:

run Docker containers
manage containerized applications

Why ECS Used?

Instead of:
deploying JARs manually,

applications run as:

Docker containers

Real-Time Example

Spring Boot microservices packaged as:

Docker Image

Then deployed using:

ECS

ECS Responsibilities

✅ Container deployment
✅ Scaling containers
✅ Load balancing
✅ Monitoring containers

Important Interview Understanding 🎯

ECS is:

AWS-managed container orchestration service

Simpler than Kubernetes.

ECS vs EC2

EC2

deploy directly on server

ECS

deploy Docker containers

✅ 4. What is EKS?

Answer:

Amazon EKS (Elastic Kubernetes Service) is AWS-managed Kubernetes service.

Used to:

deploy Kubernetes workloads
manage containerized microservices

Why EKS Used?

Large enterprise systems often use:

Kubernetes

AWS provides:
managed Kubernetes infrastructure using EKS.

Real-Time Example

Microservices deployed as:

pods
deployments
services

inside Kubernetes cluster.

EKS Advantages

✅ Kubernetes support
✅ High scalability
✅ Container orchestration
✅ Self-healing applications
✅ Rolling deployments

Important Interview Point 🎯

EKS suitable for:

complex microservices architecture
large-scale containerized systems

ECS vs EKS

Feature	ECS	EKS
Technology	AWS Native	Kubernetes
Complexity	Simpler	More Complex
Flexibility	Moderate	Very High
Kubernetes Support	No	Yes
Learning Curve	Easier	Higher

Real Interview Understanding

Use ECS when:

simpler AWS container management needed
AWS-native architecture preferred

Use EKS when:

Kubernetes expertise exists
enterprise-scale orchestration required

✅ 5. What is Auto Scaling?

Answer:

AWS Auto Scaling automatically increases or decreases resources based on traffic/load.

Real-Time Example

Suppose:

festival sale traffic increases

AWS automatically:

adds EC2 instances

When traffic reduces:

removes unnecessary instances

Benefits

✅ Cost optimization
✅ High availability
✅ Better scalability
✅ Automatic traffic handling

Example Scenario

High Traffic

2 EC2 instances → 10 EC2 instances

Low Traffic

10 EC2 instances → 2 EC2 instances

Important Interview Point 🎯

Auto Scaling works using:

CPU usage
memory
request count
custom metrics

Real Production Example

Claims application:

normal traffic → 2 instances
high traffic → auto scale to 8 instances

This prevents:

downtime
server overload

Best Final Interview Answer 🚀

EC2 provides virtual servers.

Lambda provides serverless event-driven execution.

ECS manages Docker containers.

EKS manages Kubernetes workloads.

Auto Scaling dynamically adjusts infrastructure based on traffic.

AWS Networking Interview Questions and Answers

✅ 1. What is VPC?

Answer:

Amazon VPC (Virtual Private Cloud) is a private network inside AWS cloud.

It allows us to:

isolate applications
control networking
secure resources

similar to a private data center.

Key Components of VPC

✅ Subnets
✅ Route Tables
✅ Internet Gateway
✅ NAT Gateway
✅ Security Groups

Real-Time Example

In microservices architecture:

frontend services run in public subnet
backend services run in private subnet
databases remain private

This improves security.

Important Interview Point 🎯

VPC helps:

network isolation and security.

Example Architecture

Internet

↓

Public Subnet → Load Balancer

↓

Private Subnet → Spring Boot Microservices

↓

Private DB Subnet → RDS

Common Use Cases

✅ Secure application deployment
✅ Private databases
✅ Enterprise network isolation

✅ 2. What are Security Groups?

Answer:

Security Groups act like:

virtual firewalls

for AWS resources.

Used to:

allow
deny
control

incoming and outgoing traffic.

Example

Allow:

Port 22 → SSH

Port 80 → HTTP

Port 443 → HTTPS

Port 8080 → Spring Boot App

Real-Time Example

Claims service EC2 instance:

allow traffic only from Load Balancer
deny direct internet access

This improves security.

Important Interview Point 🎯

Security Groups are:

stateful

Meaning:
if inbound traffic allowed,
response traffic automatically allowed.

Example Scenario

Mobile App

↓

Load Balancer

↓

Security Group

↓

EC2 Instance

Common Use Cases

✅ Restrict database access
✅ Protect microservices
✅ Allow only authorized traffic

✅ 3. What is Load Balancer?

Answer:

Elastic Load Balancing (ELB) distributes traffic across multiple servers.

Used for:

scalability
high availability
fault tolerance

Why Load Balancer Needed?

Without load balancer:

one server gets overloaded

With load balancer:

requests distributed evenly

Real-Time Example

Suppose:
3 EC2 instances running claims service.

Load balancer distributes requests across all instances.

Types of Load Balancers

1️⃣ Application Load Balancer (ALB)

Used for:

HTTP/HTTPS traffic
microservices routing

2️⃣ Network Load Balancer (NLB)

Used for:

ultra-high performance
TCP/UDP traffic

Example Flow

Client Request

↓

Load Balancer

↙ ↓ ↘

EC2-1 EC2-2 EC2-3

Important Interview Point 🎯

Load balancer improves:
✅ scalability
✅ fault tolerance
✅ zero downtime deployments

Real Production Example

High traffic:

load balancer distributes requests
unhealthy servers automatically removed

✅ 4. What is API Gateway?

Answer:

Amazon API Gateway is used to expose and manage APIs.

Acts as:

single entry point

for backend microservices.

Responsibilities of API Gateway

✅ Request routing
✅ Authentication
✅ Rate limiting
✅ Monitoring
✅ Request transformation

Real-Time Example

Mobile App

↓

API Gateway

↓

Claims Service

Payment Service

Policy Service

Why API Gateway Important?

Without API Gateway:

clients directly call multiple services

This creates:
❌ tight coupling
❌ security issues
❌ complex architecture

Benefits

✅ Centralized API management
✅ Better security
✅ Easier monitoring
✅ Scalability

Important Interview Point 🎯

API Gateway commonly used in:

microservices architecture

because:
it hides internal service complexity.

Real Production Features

API Gateway can provide:

JWT validation
request throttling
logging
caching
routing

Load Balancer vs API Gateway

Feature	Load Balancer	API Gateway
Main Purpose	Traffic distribution	API management
Layer	Network/Application	Application/API
Authentication	Limited	Advanced
Rate Limiting	No	Yes
Request Transformation	No	Yes
Microservices Routing	Basic	Advanced