AWS Interview Questions & Answers (2026)
These interviews test your practical knowledge of core AWS services, architecture best practices, security, and cost optimization. Demonstrate clear understanding of service limits, trade‑offs, and real‑world implementation details. Focus on concise, reasoned answers that show you can design, troubleshoot, and improve cloud solutions efficiently.
22 questions · updated Aug 29, 2026
Quick facts
| Typical rounds | Phone screen, technical deep‑dive, system design, and a final AWS‑focused coding challenge |
| Core services examined | EC2, S3, IAM, VPC, Lambda, RDS, CloudFormation, and Cost Explorer |
| Key focus areas | Security posture, scalability patterns, and cost‑effective architecture |
| Preferred experience | 2‑5 years building production workloads on AWS |
| Success metric | Ability to explain why a design choice fits the business requirement and meets AWS best practices |
Questions
Beginner
What is the difference between an IAM role and an IAM user?
An IAM user represents a permanent identity with long‑term credentials (username/password or access keys) used by a person or application. An IAM role is an identity without credentials that can be assumed by trusted entities, granting temporary security tokens. Interviewers want to hear that roles enable least‑privilege access, reduce credential leakage risk, and simplify cross‑account access, while users are suited for human operators with persistent permissions.
How does Amazon S3 achieve high durability and what trade‑offs exist with consistency?
S3 stores objects redundantly across multiple AZs, using erasure coding and checksum verification, delivering 99.999999999% durability. It provides read‑after‑write consistency for new objects and eventual consistency for overwrite and delete operations. Interviewers expect you to note that eventual consistency can cause stale reads, so applications needing immediate consistency should use versioning or DynamoDB for metadata, balancing durability against latency and complexity.
Explain the purpose of a VPC and why you would use multiple subnets.
A VPC isolates a set of AWS resources in a virtual network you control, defining IP ranges, route tables, and gateways. Multiple subnets let you separate public‑facing resources (e.g., load balancers) from private workloads (e.g., databases) and apply distinct security groups and NACLs. Interviewers look for awareness of AZ redundancy, least‑privilege networking, and the ability to design tiered architectures that limit exposure while supporting high availability.
What are the security implications of using public S3 buckets, and how can you mitigate them?
Public buckets expose data to anyone on the internet, risking data leakage, compliance violations, and potential misuse. Mitigation includes removing public ACLs, applying bucket policies that restrict access to specific principals, enabling Block Public Access settings, and using S3 Access Points with fine‑grained policies. Interviewers look for a layered approach: inventory public buckets, enforce least‑privilege, and monitor via CloudTrail and Config rules for drift.
Explain the concept of eventual consistency in DynamoDB and when it might cause issues.
DynamoDB offers eventually consistent reads that may return stale data for up to a second after a write. This improves read throughput and reduces latency. Issues arise when applications rely on immediate read‑after‑write consistency, such as inventory decrementing or financial transactions. In those cases, use strongly consistent reads or implement conditional writes. Interviewers expect you to discuss trade‑offs between consistency, latency, and cost, and how to design around them.
What is the difference between a security group and a network ACL in a VPC?
Security groups act at the instance level, are stateful (return traffic is automatically allowed), and support allow rules only. Network ACLs operate at the subnet level, are stateless (return traffic must be explicitly allowed), and support both allow and deny rules. Interviewers expect you to explain typical usage: security groups for instance‑specific access, NACLs for subnet‑wide perimeter controls, and how they combine for layered security.
Intermediate
When would you choose Amazon RDS Multi‑AZ over a single‑AZ deployment?
Multi‑AZ creates a synchronous standby in a different AZ, providing automatic failover with minimal downtime. Choose it for production databases requiring high availability, disaster recovery, and compliance with SLAs. The trade‑off is higher cost and slightly increased write latency due to synchronous replication. Interviewers expect you to discuss cost‑benefit analysis and scenarios like mission‑critical transaction processing where uptime outweighs expense.
What are the main differences between AWS Lambda and EC2 for running code?
Lambda is a serverless, event‑driven compute service that abstracts servers, scales automatically, and charges per‑invocation duration, ideal for short‑lived tasks. EC2 provides full control over OS, persistent storage, and longer‑running processes, billed per hour or second. Interviewers want you to discuss cold‑start latency, execution time limits, state management, and cost implications, showing you can select the right model based on workload characteristics.
How does AWS CloudFormation differ from Terraform, and when might you prefer one over the other?
CloudFormation is AWS‑native, using JSON/YAML templates, offering deep service integration, drift detection, and change sets. Terraform is multi‑cloud, using HCL, with a larger provider ecosystem and state management. Prefer CloudFormation when you need AWS‑specific features, seamless IAM role handling, and native rollback. Choose Terraform for multi‑cloud consistency, modularity, and when teams already use it for other providers. Interviewers look for understanding of lock‑in versus flexibility and operational impact.
Describe how you would secure data at rest and in transit for an S3 bucket used by a web application.
For data at rest, enable SSE‑S3 or SSE‑KMS encryption, optionally using bucket policies to enforce encryption. For data in transit, enforce HTTPS via bucket policy or CloudFront with an OAI, and enable TLS 1.2+. Additionally, use IAM policies limiting access to specific IAM roles, enable versioning, and configure MFA delete for extra protection. Interviewers expect you to mention defense‑in‑depth, compliance considerations, and how each control mitigates specific threats.
When would you use Amazon DynamoDB over Amazon RDS?
Choose DynamoDB for workloads requiring single‑digit millisecond latency at any scale, flexible schema, and seamless auto‑scaling without managing servers. It excels for key‑value or document patterns, such as session stores or IoT telemetry. RDS is better for relational data, complex queries, joins, and ACID transactions. Interviewers expect you to discuss cost per request versus instance pricing, consistency models, and operational overhead, showing you can match data model to service strengths.
How does AWS Auto Scaling differ from Elastic Load Balancing, and how do they work together?
Auto Scaling automatically adjusts the number of EC2 instances based on defined metrics (CPU, network, custom CloudWatch alarms). Elastic Load Balancing distributes incoming traffic across those instances, ensuring high availability. Together, Auto Scaling ensures capacity matches demand, while ELB provides a stable endpoint. Interviewers want you to explain health checks, scaling policies, and how scaling actions trigger ELB target registration, highlighting the feedback loop that maintains performance and cost efficiency.
Explain how AWS WAF works and a common rule set you would implement for a public web service.
AWS WAF attaches to CloudFront or an Application Load Balancer, inspecting incoming HTTP requests against rule groups. A common rule set includes IP reputation lists, SQL injection detection, and cross‑site scripting filters. You can also rate‑limit requests to mitigate DDoS attacks. Interviewers look for understanding of rule priority, action (allow, block, count), and how WAF integrates with CloudWatch for monitoring and automated response.
What are the benefits and limitations of using AWS Fargate for container workloads?
Fargate abstracts server management, allowing you to run containers without provisioning EC2 instances, which simplifies operations and improves security isolation. Benefits include per‑second billing, automatic scaling, and reduced patching overhead. Limitations involve higher cost compared to self‑managed EC2, limited control over underlying hardware, and constraints on networking (e.g., ENI limits). Interviewers expect you to compare Fargate to ECS on EC2, discussing when operational simplicity outweighs cost and flexibility concerns.
How does Amazon CloudWatch differ from AWS X-Ray, and when would you use each?
CloudWatch collects metrics, logs, and events for infrastructure and services, providing alarms and dashboards. X-Ray traces requests across services, offering detailed latency breakdowns and pinpointing bottlenecks in distributed applications. Use CloudWatch for overall health monitoring and alerting; use X-Ray when you need end‑to‑end visibility into request flow, especially for microservices or serverless architectures. Interviewers want you to discuss integration, cost, and the complementary nature of the two tools.
Advanced
What is a NAT Gateway and when would you use it instead of a NAT instance?
A NAT Gateway is a managed AWS service that provides outbound internet access for private subnets without exposing private IPs. It offers higher bandwidth, automatic scaling, and reduced maintenance compared to a self‑managed NAT instance, which requires patching, monitoring, and capacity planning. Use a NAT Gateway for production workloads needing reliable, high‑throughput egress; choose a NAT instance for cost‑sensitive, low‑traffic scenarios where you need custom routing or firewall rules.
Explain how AWS Cost Explorer can be used to identify and reduce unnecessary spend.
Cost Explorer visualizes usage and cost trends across services, accounts, and tags. By filtering on under‑utilized resources (e.g., low‑CPU EC2 instances, idle RDS instances) and examining Reserved Instance (RI) coverage, you can pinpoint waste. Combine with rightsizing recommendations and tag‑driven allocation to re‑architect or terminate idle assets. Interviewers want you to discuss actionable steps: enable detailed billing, apply cost allocation tags, and set budget alerts to enforce ongoing governance.
How does AWS Step Functions help orchestrate serverless workflows, and what are its limits?
Step Functions coordinate Lambda functions, ECS tasks, and other services via a state machine defined in Amazon States Language. It provides visual debugging, error handling, and retries, enabling complex business logic without custom code. Limits include a maximum of 25,000 state transitions per execution and a 90‑day execution duration. Interviewers expect you to discuss when to use Step Functions versus EventBridge or custom orchestration, emphasizing maintainability and observability benefits.
What is the purpose of AWS Organizations and how does Service Control Policies (SCPs) differ from IAM policies?
AWS Organizations lets you centrally manage multiple AWS accounts, applying consolidated billing and governance. SCPs are guardrails that restrict what services and actions any account can perform, regardless of IAM permissions. Unlike IAM policies, which grant permissions, SCPs only limit them, ensuring compliance across the organization. Interviewers look for awareness of hierarchy—root, OU, account—and how SCPs enforce security posture while IAM handles role‑based access within those bounds.
What is AWS GuardDuty and how does it complement traditional security tools?
GuardDuty is a threat detection service that continuously analyzes VPC Flow Logs, CloudTrail events, and DNS logs using machine learning to identify suspicious activity. It complements traditional firewalls and SIEMs by providing managed, real‑time insights without requiring additional agents. Interviewers want you to mention findings categories (e.g., compromised keys, port scanning), integration with CloudWatch Events for automated remediation, and how it reduces the operational burden of threat hunting.
How would you design a highly available web application using AWS services?
Deploy the front end on an Elastic Load Balancer across multiple AZs, with Auto Scaling groups for EC2 or use Lambda behind API Gateway for serverless. Store static assets in S3 with CloudFront CDN for global edge caching. Use RDS Multi‑AZ for the database, and enable read replicas for scaling reads. Add Route 53 health‑checked DNS failover and enable backups and snapshots. Interviewers look for redundancy at each tier, automated failover, and cost‑effective scaling.
What is the purpose of AWS Snowball, and when would you choose it over Direct Connect?
Snowball is a physical data transfer appliance used to move petabyte‑scale data to AWS when network bandwidth is insufficient or costly. Direct Connect provides dedicated network links for ongoing transfers but requires infrastructure and can be expensive for one‑time bulk migrations. Choose Snowball for large, infrequent migrations, especially in remote locations, whereas Direct Connect suits continuous, high‑throughput workloads. Interviewers expect you to discuss security (encryption at rest), data validation, and cost‑benefit analysis.
Common mistakes
- Confusing IAM roles with users and granting excessive permissions
- Assuming S3 is always private without verifying bucket policies
- Over‑provisioning EC2 instances instead of using auto‑scaling or serverless options
- Neglecting cost‑optimization tools like Reserved Instances and Savings Plans
- Ignoring eventual consistency implications in DynamoDB or S3 overwrites
Study plan
- Review core services (EC2, S3, IAM, VPC) and practice explaining their limits and best practices
- Build a sample multi‑AZ architecture in a personal AWS account, documenting security groups, subnets, and failover
- Solve 10+ hands‑on labs focusing on Lambda, Step Functions, and DynamoDB consistency patterns
- Analyze Cost Explorer reports and create a rightsizing plan for a mock workload
- Mock interview with a peer, focusing on concise, reasoning‑driven answers for each difficulty level
FAQ
How many AWS interview rounds are typical?
Most companies run 3‑5 rounds: an initial phone screen, a technical deep‑dive, a system‑design interview, and sometimes a final AWS‑focused coding or troubleshooting session.
Do I need AWS certifications to pass the interview?
Certifications help but are not required. Demonstrating practical experience, clear reasoning, and knowledge of best practices matters more than a badge.
What should I bring to an AWS interview?
Bring a notebook with key service limits, a list of personal AWS projects, and prepared stories that show how you solved scaling, security, or cost challenges.
How important is cost‑optimization knowledge?
Very important. Interviewers often ask how you would reduce spend, so be ready to discuss Reserved Instances, Savings Plans, rightsizing, and monitoring tools.
Can I use third‑party tools during the interview?
Usually not. Expect to answer conceptually and, if asked, write simple pseudo‑code or architecture diagrams on a whiteboard or shared screen.
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