AWS Interview Questions For Cloud, Data, and Backend Roles

AWS (Amazon Web Services) is a cloud platform offering on-demand compute, storage, database, and networking. Core services include EC2 (virtual servers), S3 (object storage), RDS (managed databases), Lambda (serverless functions), and IAM (access control).

A region is a geographic area (like Mumbai or N. Virginia) containing multiple, isolated availability zones. An availability zone is one or more discrete data centers within a region. Spreading resources across zones gives high availability.

S3 is scalable object storage for files of any size. It's used for backups, static websites, data lakes, and storing images or logs. Objects live in buckets and are accessed by key, with strong durability and lifecycle rules.

EC2 (Elastic Compute Cloud) provides resizable virtual servers in the cloud. You choose an instance type for CPU/memory, an AMI for the OS, and pay per second/hour. Use it when you need full control over the server environment.

EC2 gives you a persistent virtual server you manage and pay for while it runs. Lambda is serverless — it runs your function on demand, scales automatically, and you pay only per invocation and duration. Use Lambda for short, event-driven tasks.

IAM (Identity and Access Management) controls who can do what in your account through users, groups, roles, and policies. Best practice is least privilege — grant only the permissions needed — and using roles instead of long-lived access keys.

A security group is a stateful firewall attached to an instance — return traffic is automatically allowed. A network ACL is a stateless firewall at the subnet level where you must allow both inbound and outbound rules explicitly.

S3 offers Standard (frequent access), Standard-IA and One Zone-IA (infrequent access), Intelligent-Tiering (auto-moves data), and Glacier/Glacier Deep Archive (cheap archival with slower retrieval). Lifecycle rules move data between them to save cost.

RDS is a managed relational database (MySQL, PostgreSQL, etc.) with SQL and joins. DynamoDB is a managed NoSQL key-value/document store with single-digit-millisecond latency and automatic scaling. Choose RDS for relational data, DynamoDB for high-scale key lookups.

Auto Scaling automatically adds or removes EC2 instances based on demand using policies tied to metrics like CPU. Combined with a load balancer, it keeps performance steady during spikes and reduces cost during quiet periods.

SQS is a message queue where consumers pull messages and process them one at a time (decoupling and buffering). SNS is a pub/sub service that pushes a message to many subscribers at once. They're often combined in fan-out patterns.

A VPC (Virtual Private Cloud) is your isolated network in AWS. You define subnets (public/private), route tables, internet and NAT gateways, and security controls, giving you fine-grained control over how resources connect to each other and the internet.

Common ones are S3 (data lake), Glue (serverless ETL and catalog), EMR (managed Spark/Hadoop), Redshift (data warehouse), Athena (query S3 with SQL), Kinesis (streaming), and Lambda for lightweight transforms.

Redshift is a columnar, massively parallel data warehouse for analytics on large datasets. Use it for BI and reporting workloads that aggregate billions of rows, where it outperforms row-based OLTP databases like RDS.