Amazon Web Services (AWS) is the largest public cloud platform, so AWS skills appear in job descriptions for cloud, DevOps, security and backend roles. These AWS interview questions and answers cover the services and concepts interviewers ask about most, from compute and storage to networking, security and architecture.
Core concepts
1. What is AWS?
AWS is Amazon’s cloud computing platform. It offers on-demand services, including compute, storage, databases, networking, analytics and AI, with pay-as-you-go pricing.
2. Explain IaaS, PaaS and SaaS with AWS examples.
- IaaS: you manage the operating system and above, as with Amazon EC2.
- PaaS: AWS manages the platform, as with Elastic Beanstalk or RDS.
- SaaS: a complete application, such as Amazon Connect for contact centres.
3. How are Regions and Availability Zones different?
A Region is a geographic area, such as Mumbai (ap-south-1). Each Region contains several Availability Zones (AZs): separate data centres with independent power and networking. Deploying across AZs protects against a single data-centre failure.
4. Describe the shared responsibility model.
AWS secures the cloud itself: hardware, facilities and core infrastructure. Customers, by contrast, secure what they put in the cloud: data, identities, operating systems, network rules and application settings.
Compute
5. What is Amazon EC2?
EC2 provides virtual servers, called instances. You choose the instance type, operating system, storage and network settings.
6. Compare EC2 purchasing options.
| Option | Best for |
|---|---|
| On-Demand | Short-term or unpredictable workloads |
| Savings Plans and Reserved Instances | Steady workloads, with large discounts for commitment |
| Spot Instances | Fault-tolerant jobs, using spare capacity at low prices |
| Dedicated Hosts | Licensing or compliance needs |
7. When would you use AWS Lambda?
Lambda runs code without servers, triggered by events such as an S3 upload or an API call. You pay per request and run time. Each invocation can run for up to 15 minutes.
8. How does Auto Scaling work?
An Auto Scaling group adds or removes EC2 instances based on metrics, such as CPU use, or on a schedule. As a result, you match capacity to demand.
Storage and databases
9. What is Amazon S3?
S3 is object storage. It stores files as objects in buckets and is designed for 99.999999999% (eleven nines) durability. Storage classes, such as Standard, Intelligent-Tiering, Glacier Instant Retrieval and Glacier Deep Archive, balance cost and access speed.
10. S3 vs EBS vs EFS?
- S3: object storage, accessed over HTTPS.
- EBS: block storage attached to one EC2 instance, like a virtual disk.
- EFS: a shared file system that many instances can mount over NFS.
11. RDS vs DynamoDB?
RDS runs managed relational databases, such as MySQL, PostgreSQL and SQL Server. DynamoDB, on the other hand, is a fully managed NoSQL key-value and document database built for very high scale and low latency.
Networking
12. What is a VPC?
A Virtual Private Cloud is your own isolated network in AWS. You define IP ranges, subnets, route tables and gateways.
13. Security groups vs network ACLs?
| Security group | Network ACL |
|---|---|
| Applies to instances (network interfaces) | Applies to subnets |
| Stateful: return traffic is allowed automatically | Stateless: you must allow return traffic |
| Allow rules only | Allow and deny rules |
14. Which load balancers does AWS offer?
- Application Load Balancer: layer 7, for HTTP and HTTPS, with path-based routing.
- Network Load Balancer: layer 4, for very high performance TCP and UDP.
- Gateway Load Balancer: for third-party virtual appliances, such as firewalls.
15. What does Route 53 do?
Route 53 is AWS’s DNS service. It also registers domains and supports routing policies, such as latency-based, weighted and failover routing.
Security and monitoring
16. What is IAM?
Identity and Access Management controls who can do what in your account. It uses users, groups, roles and policies. Best practice is to use roles and temporary credentials, enforce MFA and follow least privilege.
17. CloudWatch vs CloudTrail?
CloudWatch collects metrics, logs and alarms about resources and applications. CloudTrail, in contrast, records API calls: who did what, when and from where.
18. How do you secure an S3 bucket?
Keep Block Public Access on, use bucket policies and IAM with least privilege, enable encryption and versioning, and log access. Read more in our guide to securing a Linux server on AWS EC2.
Architecture
19. Name the six pillars of the Well-Architected Framework.
Operational excellence, security, reliability, performance efficiency, cost optimisation and sustainability.
20. How would you design a highly available web application?
Use an Application Load Balancer across at least two AZs, EC2 instances or containers in an Auto Scaling group, a Multi-AZ RDS database, S3 for static files with CloudFront in front, and Route 53 health checks.
Keep preparing
Practise each answer out loud, and run the commands in a lab rather than memorising them. Interviewers often ask follow-up questions, so make sure you understand why each answer is true.
Sources
Preparing for an interview? Browse more questions in our interview preparation hub. For businesses, we also offer security services such as VAPT, server hardening and ISO 27001 readiness.
