25+ AWS Interview Questions & Answers (2025) for Experienced Professionals

list of 25 essential AWS interview questions and answers for experienced professionals, optimized for clarity and technical depth:

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Core AWS Services

1. Q: Explain the difference between EC2 and Lambda.
   A:

• EC2: Virtual servers you manage (persistent, scalable)
• Lambda: Serverless functions (event-driven, auto-scaling, pay-per-execution)

1. Q: What is an S3 bucket? How does versioning work?
   A:

• S3: Object storage for files
• Versioning: Keeps multiple variants of an object (protects against accidental deletes)

1. Q: When would you use RDS vs DynamoDB?
   A:

• RDS: SQL/relational data (structured queries)
• DynamoDB: NoSQL (scalable, low-latency key-value store)

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Networking & Security

4. Q: What is a VPC? Key components?
   A:

• Virtual Private Cloud: Isolated AWS network
• Components: Subnets, Route Tables, NACLs, Security Groups

4. Q: Explain IAM roles vs policies.
   A:

• IAM Role: Temporary credentials for AWS services/users
• IAM Policy: JSON document defining permissions

4. Q: How does AWS Shield protect against DDoS?
   A:

• Standard: Free layer 3/4 protection
• Advanced: Paid (layer 7 protection + WAF integration)

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Scalability & Performance

7. Q: What is Auto Scaling? Components?
   A:

• Automatically adjusts EC2 capacity
• Components: Launch Configurations, Scaling Policies, Target Groups

7. Q: How does ELB differ from ALB/NLB?
   A:

• ELB (Classic): Legacy load balancer
• ALB: Layer 7 (HTTP/HTTPS), NLB: Layer 4 (TCP/UDP)

7. Q: What is CloudFront? How does caching work?
   A:

• CDN for fast content delivery
• Caching: Uses Edge Locations (TTL-based)

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DevOps & Automation

10. Q: Explain CI/CD pipeline using AWS services.
    A:
    • CodeCommit → CodeBuild → CodeDeploy → CodePipeline
    • Alternatives: Jenkins + AWS integrations
11. Q: What is CloudFormation vs Terraform?
    A:
    • CloudFormation: AWS-native (YAML/JSON)
    • Terraform: Multi-cloud (HCL syntax)
12. Q: How does AWS EKS manage Kubernetes?
    A:
    • Managed control plane + worker nodes (EC2 or Fargate)

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Database & Storage

13. Q: When to use ElastiCache?
    A:
    • Caching layer for high-read applications (Redis/Memcached)
14. Q: What is EBS vs EFS?
    A:
    • EBS: Block storage (attached to EC2)
    • EFS: File storage (multi-AZ, NFS)
15. Q: How does Aurora improve over RDS?
    A:
    • 5x faster, auto-scaling storage, multi-master replication

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Advanced Topics

16. Q: What is AWS Lambda cold start? How to mitigate?
    A:
    • Delay when Lambda initializes
    • Fix: Provisioned Concurrency, smaller packages
17. Q: Explain VPC Peering vs Transit Gateway.
    A:
    • Peering: 1:1 connection between VPCs
    • Transit Gateway: Hub-and-spoke model
18. Q: What is AWS Organizations? Use cases?
    A:
    • Manage multiple AWS accounts
    • Use cases: Consolidated billing, SCPs for security

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Monitoring & Cost Optimization

19. Q: Key differences between CloudWatch and CloudTrail?
    A:
    • CloudWatch: Metrics/logs (performance)
    • CloudTrail: API call history (governance)
20. Q: How to reduce AWS costs?
    A:
    • Reserved Instances, Spot Instances, S3 lifecycle policies
21. Q: What is Trusted Advisor?
    A:
    • AWS tool for cost/security/performance recommendations

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Serverless & Containers

22. Q: When to use Fargate vs EC2 for ECS?
    A:
    • Fargate: Serverless (no node management)
    • EC2: More control (cost-optimized for long-running)
23. Q: Explain SQS vs SNS.
    A:
    • SQS: Queue (pull-based)
    • SNS: Pub/Sub (push-based)
24. Q: What is AWS Step Functions?
    A:
    • Orchestrates Lambda functions (state machines)

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Final Question

25. Q: How do you secure an AWS environment?A:
    • IAM least privilege, encryption (KMS), VPC flow logs, GuardDuty