Top AWS Interview Questions and Answers (2026)
Cloud interviews lean heavily on trade-offs. Memorising service names won't help — being able to explain when to use one over another will.
Q01.What are the core compute services on AWS?
EC2 (virtual machines), Lambda (functions-as-a-service), ECS and EKS (containers), Fargate (serverless containers). Choose by operational ownership and runtime model.
Q02.Difference between S3 and EBS?
S3 is object storage accessed via HTTP — unlimited scale, eventual consistency for some operations. EBS is block storage attached to an EC2 instance, low-latency, single-AZ.
Q03.What is an IAM role and when do you use it?
A role is an identity with policies that any trusted entity (EC2 instance, Lambda, another account) can temporarily assume. Use roles for workloads — never embed access keys.
Q04.Difference between security groups and NACLs?
Security groups are stateful firewalls at the instance level. NACLs are stateless rules at the subnet level. Use SGs for application access, NACLs for coarse subnet defence.
Q05.What is a VPC?
A logically isolated network in AWS. You define IP ranges, subnets, route tables and gateways — like running your own data centre's network with software.
Q06.Public vs private subnet?
A public subnet has a route to an internet gateway. A private subnet does not — outbound internet from private subnets needs a NAT gateway.
Q07.What is Auto Scaling?
A service that adds or removes EC2 instances based on metrics like CPU or request count, keeping fleet size aligned with demand.
Q08.What does CloudFront do?
It's a CDN that caches your content at AWS edge locations close to users, reducing latency and origin load.
Q09.Difference between RDS and DynamoDB?
RDS is managed relational databases (Postgres, MySQL, etc.). DynamoDB is managed key-value/document NoSQL with single-digit-millisecond latency at any scale.
Q10.What is CloudFormation?
AWS's infrastructure-as-code service. You declare resources in YAML/JSON and AWS provisions and updates them as a stack.
Q11.What is Lambda?
Serverless functions billed per invocation and duration. You upload code, AWS runs it on demand without provisioning servers.
Q12.What is SQS used for?
A managed message queue that decouples producers and consumers, smoothing out spikes and enabling retries.
Q13.Difference between SNS and SQS?
SNS is pub/sub — one message to many subscribers. SQS is point-to-point — one consumer pulls each message.
Q14.What is CloudWatch?
AWS's monitoring service — metrics, logs, alarms and dashboards across services and applications.
Q15.What is the shared responsibility model?
AWS secures the cloud (hardware, networking, hypervisors). You secure what's in the cloud (IAM, encryption, application code, OS patches on EC2).
Q16.How do you secure data at rest in S3?
Enable server-side encryption (SSE-S3, SSE-KMS or SSE-C), enforce TLS via bucket policy, block public access by default, and audit with S3 Access Logs or CloudTrail.
Q17.What is the difference between scaling up and scaling out?
Scaling up (vertical) means a bigger instance. Scaling out (horizontal) means more instances. Horizontal scaling is preferred for resilience.
Q18.Explain Route 53 routing policies.
Simple, weighted, latency-based, geolocation, failover and multi-value. They control how DNS responses are chosen for a query.
Q19.What is the Well-Architected Framework?
AWS's set of best-practice pillars: operational excellence, security, reliability, performance efficiency, cost optimisation and sustainability.
Q20.How would you reduce AWS costs?
Right-size instances, switch to Graviton, use Savings Plans / Reserved Instances, delete idle resources, enable S3 lifecycle policies, and review CloudWatch + Cost Explorer monthly.
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