AWS Questions and Answers

 

1️⃣ What is the difference between EC2 and ECS?

🔹 Amazon EC2

Amazon EC2 provides virtual servers in the cloud.

You:

  • Manage OS

  • Install dependencies

  • Configure Nginx, Gunicorn

  • Handle scaling manually (or via Auto Scaling)

👉 Suitable for traditional deployments.

🔹 Amazon ECS

Amazon ECS is a container orchestration service.

You:

  • Deploy Docker containers

  • Don’t manage servers directly

  • Scale containers easily

👉 Suitable for Dockerized applications.

Key Differences

EC2ECS
Virtual machines            Container orchestration
Manual server management            Managed container scheduling
More control            More automation
Good for legacy apps            Best for microservices

If your app is Dockerized → recommend ECS.
If simple and small scale → EC2 is fine.

2️⃣ How Does Auto Scaling Work?

Amazon EC2 Auto Scaling automatically adjusts the number of EC2 instances based on load.

How It Works:

  1. Define a Launch Template (AMI + instance type)

  2. Create Auto Scaling Group (ASG)

  3. Attach scaling policies

  4. Monitor metrics via Amazon CloudWatch

Example:

  • If CPU > 70% → Add new instance

  • If CPU < 30% → Remove instance

Backend Scenario:

During sale traffic:

  • Instances scale from 2 → 6 automatically

  • Load balancer distributes traffic

3️⃣ What is IAM Role vs IAM User?

Using AWS Identity and Access Management (IAM):

🔹 IAM User

  • Permanent identity

  • Used by humans

  • Has username + password or access keys

Example:
Developer logging into AWS console.

🔹 IAM Role

  • Temporary permissions

  • Assigned to AWS services

  • No password or long-term credentials

Example:
EC2 instance accessing S3.

Use IAM Role for services.
Avoid hardcoding access keys inside applications.

4️⃣ How Does S3 Ensure Durability?

Amazon S3 provides 11 9’s durability (99.999999999%).

How?

  • Stores objects across multiple devices

  • Data replicated across multiple Availability Zones

  • Automatic integrity checks

  • Self-healing storage

Backend Use Case:

  • User profile images

  • Invoices

  • Backups

  • Static files

If one data center fails → data is still safe.

5️⃣ What is Multi-AZ in RDS?

Amazon RDS Multi-AZ deployment:

  • Primary database runs in one Availability Zone

  • Standby replica runs in another AZ

  • Automatic failover if primary fails

Why Important?

Prevents downtime in:

  • Server crashes

  • Network failure

  • Maintenance events

Multi-AZ = High Availability

Read Replica = Performance Scaling

Don’t confuse them.

6️⃣ How to Design a High-Availability API Architecture?

This is a very common system design question.

🔹 Components Required:

  • Amazon Route 53 – DNS

  • Elastic Load Balancing – Traffic distribution

  • Amazon EC2 Auto Scaling – App scaling

  • Amazon RDS – Multi-AZ DB

  • Amazon S3 – Media storage

  • Amazon CloudWatch – Monitoring

 Architecture Flow:

Users
   ↓
Route 53
   ↓
Load Balancer
   ↓
Auto Scaling EC2 Instances (Django)
   ↓
RDS (Multi-AZ)
   ↓
S3 (Media Files)
   ↓
CloudWatch Monitoring

Key Design Principles:
✔ No single point of failure
✔ Multi-AZ deployment
✔ Horizontal scaling
✔ Separate DB from app server
✔ Store files outside EC2
✔ Enable monitoring & alerts
1️⃣ What is the difference between ECS and EKS?
🔹 Amazon ECS
Amazon ECS is AWS’s native container orchestration service.
  • Fully managed by AWS
  • Easier to set up
  • Deep AWS integration
  • Uses task definitions
  • No need to manage Kubernetes control plane
👉 Best for teams that want simplicity and tight AWS integration.
🔹 Amazon EKS
Amazon EKS is a managed Kubernetes service.
  • Runs standard Kubernetes
  • Portable across cloud providers
  • More flexible
  • Steeper learning curve
Best for microservices, large-scale systems, or multi-cloud strategy.
ECSEKS
AWS-native            Kubernetes-based
Easier setup            More complex
Good for simple Docker apps            Best for microservices
Less portability            Cloud portable

If company already uses Kubernetes → choose EKS.
If simple Docker-based app → ECS is faster and easier.

2️⃣ How Does VPC Work?
Amazon VPC (Virtual Private Cloud) is your private network inside AWS.
Think of it as your own data center network.
Core Components:
  • Subnets (Public & Private)
  • Route Tables
  • Internet Gateway
  • NAT Gateway
  • Security Groups
  • Network ACLs
Example Architecture:
VPC
 ├── Public Subnet (Load Balancer)
 ├── Private Subnet (EC2 App Servers)
 └── Private Subnet (RDS Database)
How It Works:
  1. You create a VPC.
  2. Define IP range (CIDR block).
  3. Create subnets inside it.
  4. Attach Internet Gateway for public access.
  5. Use Security Groups to control traffic.
3️⃣ What is NAT Gateway?
NAT Gateway allows private subnet instances to access the internet without being publicly accessible.
Why Needed?
Example:
Your EC2 app server is in a private subnet.
It needs to:
  • Install packages
  • Access third-party APIs
  • Pull Docker images
But you don’t want it publicly exposed.
4️⃣ How Do You Secure a Public API on AWS?
This is a very common backend interview question.
Here’s a production-ready answer:
Step 1: Use HTTPS
Use:
  • SSL via ACM
  • Attach certificate to Load Balancer
Step 2: Use Security Groups
Allow:
  • Port 443 (HTTPS)
  • Restrict SSH (22) to your IP only
Step 3: Put EC2 in Private Subnet
  • Only Load Balancer should be public.
  • EC2 should not have public IP.
Step 4: Use IAM Roles
Use:
AWS Identity and Access Management
Never store:
  • AWS keys in code
  • Secrets in GitHub
Step 5: Enable WAF
Use:
AWS WAF
Protect against:
  • SQL Injection
  • XSS
  • DDoS
  • Bot attacks
Step 6: Rate Limiting
Use:
  • API Gateway throttling
  • Load Balancer rules
  • Application-level rate limiting
5️⃣ How to Reduce AWS Cost in Production?
Very important for senior roles.
1. Use Right Instance Types
Choose:
  • t3/t4g for small apps
  • Avoid over-provisioning
2. Enable Auto Scaling
Use:
Amazon EC2 Auto Scaling
Scale down during low traffic.
3. Use Reserved Instances / Savings Plans
Commit long-term usage for:
  • RDS
  • EC2
Save up to 30–60%.
4. Use S3 Lifecycle Policies
With:
Amazon S3
Move old files to:
  • S3 Glacier
  • Infrequent Access
5. Monitor with Cost Explorer
Use:
AWS Cost Explorer
Track:
  • Unused resources
  • Idle load balancers
  • Unattached EBS volumes
6. Turn Off Non-Production Environments
Stop:
  • Dev EC2 at night
  • Unused test databases
To reduce AWS cost:
  • Right-size resources
  • Enable auto scaling
  • Use reserved pricing
  • Monitor usage regularly
  • Remove unused infrastructure

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