AWS Interview Questions

Top 20 Frequently Asked AWS Interview Questions (Including EMR)

1. What is AWS and what are its core services?

AWS (Amazon Web Services) is a cloud computing platform that provides on-demand infrastructure and services.
Core Services include:

• Compute – EC2, Lambda
• Storage – S3, EBS, Glacier
• Databases – RDS, DynamoDB, Redshift
• Networking – VPC, Route 53, CloudFront

2. What are the differences between Regions and Availability Zones (AZs)?

Region: A geographical area (e.g., us-east-1, ap-south-1).
Availability Zone (AZ): Isolated data centers within a region for high availability.
Example: us-east-1 has 6 AZs.

3. What is IAM (Identity and Access Management) and why is it important?

IAM helps manage users, groups, and permissions securely.

• Provides least privilege access
• Supports MFA (Multi-Factor Authentication)
• Uses policies to control access

4. Explain the concept of EC2 and the different types of EC2 instances.

EC2 (Elastic Compute Cloud) provides resizable compute capacity in the cloud.
Types:

• General Purpose – t3, m5
• Compute Optimized – c5
• Memory Optimized – r5, x1
• Storage Optimized – i3, d2
• Accelerated Computing – p3, g4 (GPU/AI workloads)

5. What are Security Groups and how do they differ from Network ACLs?

Security Groups: Instance-level firewall, stateful (return traffic is automatically allowed).
NACLs: Subnet-level firewall, stateless (return traffic must be explicitly allowed).

6. What is the difference between S3 Standard, S3 IA, and S3 Glacier?

• S3 Standard: For frequently accessed data
• S3 IA (Infrequent Access): Lower cost for rarely accessed data
• S3 Glacier: Archival storage, very cheap, but retrieval is slow (minutes–hours)

7. How does Auto Scaling work in AWS?

Auto Scaling automatically adjusts the number of EC2 instances based on demand.
Scaling Policies:

• Dynamic Scaling
• Predictive Scaling
• Scheduled Scaling

It uses CloudWatch metrics like CPU utilization.

8. What is the difference between Elastic Load Balancer (ELB) types: Classic, ALB, and NLB?

• Classic Load Balancer (CLB): Works at request & connection level (Layer 4 & 7)
• Application Load Balancer (ALB): Works at Layer 7, supports path & host-based routing
• Network Load Balancer (NLB): Works at Layer 4, provides high performance & low latency

9. What is Amazon VPC and how is it different from a default VPC?

VPC: Virtual Private Cloud — your own isolated network in AWS.
Default VPC: Comes pre-configured with subnets, IGW, and security groups.
Custom VPC: Fully user-defined, offering complete control.

10. Explain the shared responsibility model in AWS.

AWS Responsibility: Security of the cloud (infrastructure, hardware).
Customer Responsibility: Security in the cloud (applications, data, IAM).

11. What is Amazon RDS and how does it differ from Amazon Aurora?

RDS: Managed relational database service (MySQL, PostgreSQL, Oracle, SQL Server, MariaDB).
Aurora: AWS’s own high-performance DB engine, MySQL/PostgreSQL compatible, auto-scaling, 5x faster than MySQL.

12. What is DynamoDB and how does it handle scalability?

DynamoDB is a fully managed NoSQL database.
Scalability:

• Auto-scales throughput with On-Demand or Auto Scaling mode
• Supports Global Tables for multi-region replication

13. Explain the difference between EBS and Instance Store volumes.

EBS (Elastic Block Store): Persistent storage, survives instance stop/start, good for databases.
Instance Store: Temporary storage tied to EC2 lifecycle, data lost when stopped, good for cache/scratch space.

14. What is Amazon Redshift and when should you use it?

Amazon Redshift is AWS’s managed data warehouse.
Use cases: Analytics on petabyte-scale structured data.
Uses columnar storage, compression, and parallel queries for performance.

15. What is Amazon EMR and how does it work?

Amazon EMR (Elastic MapReduce) is a managed big data platform.
Features:

• Supports Hadoop, Spark, Hive, HBase, Presto, Flink
• Automatically provisions and manages clusters
• Scales compute up/down as needed
• Use cases: ETL, log analysis, ML training

16. What is AWS Glue and how does it compare to EMR?

AWS Glue: Serverless ETL service, automatically discovers & transforms data.
Amazon EMR: Full-fledged cluster for big data workloads.
➡️ Use Glue for lightweight ETL, EMR for large-scale processing.

17. What is Amazon Kinesis and its use cases?

Amazon Kinesis is a real-time data streaming service.
Components:

• Kinesis Data Streams – real-time ingest
• Kinesis Data Firehose – delivery to S3, Redshift, Elasticsearch
• Kinesis Analytics – real-time SQL-based processing

Use cases: IoT data, log ingestion, video streams.

18. What is AWS CloudTrail and how is it different from CloudWatch?

CloudTrail: Logs API calls and account activity.
CloudWatch: Monitors metrics & logs, creates dashboards & alarms.

19. How do you secure data at rest and in transit in AWS?

At Rest: KMS encryption, EBS/S3/RDS encryption.
In Transit: SSL/TLS certificates (ACM), HTTPS, secure VPC endpoints.

20. What are AWS Well-Architected Framework pillars?

• Operational Excellence
• Security
• Reliability
• Performance Efficiency
• Cost Optimization
• Sustainability