DevOps, Docker & AWS
The infrastructure side of a backend interview — AWS fundamentals (EC2, S3, VPC, IAM, RDS, DynamoDB, Lambda), and Docker from first principles through images, networking, volumes, and production security.
AWS Fundamentals
What is AWS? What are the main categories of AWS services?
beginnerTests whether you have a basic map of compute, storage, database, and networking service categories on AWS.
What is the difference between a Region, Availability Zone, and Edge Location?
beginnerTests whether you know AWS's physical infrastructure hierarchy and why it matters for latency and fault tolerance.
What is the AWS Shared Responsibility Model?
beginnerTests whether you know exactly where AWS's security responsibility ends and the customer's begins.
What is the AWS Well-Architected Framework? Name the 6 pillars.
intermediateTests whether you know the framework AWS itself uses to evaluate architecture quality across reliability, security, and cost.
Git & GitHub
Your PR has conflicts with main. What do you do?
beginnerTests whether you know the basic pull-rebase-resolve-push workflow every engineer needs cold.
You accidentally deleted a branch with unmerged commits. Can you recover it?
intermediateTests whether you know git reflog can rescue commits even after the branch pointer itself is gone.
What is the difference between HEAD, ORIG_HEAD, and FETCH_HEAD in Git?
intermediateTests whether you know these three references track genuinely different things during risky Git operations.
What is the difference between lightweight and annotated tags in Git? Why is annotated preferred for releases?
intermediateTests whether you know annotated tags carry metadata (author, message, signature) that lightweight tags don't.
How do you ensure Git history is audit-friendly for compliance purposes?
intermediateTests whether you know signed commits, linear history, and mandatory PR reviews all contribute to an auditable trail.
How do you ensure secrets are never accidentally committed to a Git repository?
intermediateTests whether you know secret scanning, pre-commit hooks, and .gitignore each catch a different failure mode.
A commit passed all tests locally but failed CI on GitHub. What do you do?
beginnerTests whether you go straight to CI logs and reproduce locally, instead of just re-pushing and hoping.
EC2 & S3
What is EC2? What are its key features?
beginnerTests whether you know the basics of AWS's core virtual machine service.
What is the difference between On-Demand, Reserved, Spot, and Dedicated instances?
beginnerTests whether you know the cost-versus-commitment-versus-interruption-risk tradeoff across EC2's four purchase models.
What are the S3 storage classes?
beginnerTests whether you know how access frequency and retrieval time trade off against storage cost across S3's tiers.
What is an S3 Pre-Signed URL? How does it enable temporary access?
intermediateTests whether you know how to grant time-limited access to a private S3 object without changing bucket permissions.
CI/CD Pipelines
What is CI/CD? What does Continuous Integration and Continuous Delivery/Deployment actually mean in practice?
beginnerTests whether you know the distinction between Delivery (ready to deploy) and Deployment (auto-deployed) specifically.
How do you write a GitHub Actions workflow that builds and tests a Spring Boot application?
intermediateTests whether you can actually write the YAML, not just describe CI/CD conceptually.
How do you add a Docker build-and-push step to a GitHub Actions pipeline, and what's the difference between DockerHub, AWS ECR, and GitHub Container Registry?
intermediateTests whether you know how to wire the build step and where to actually push the resulting image.
How do you securely pass secrets (AWS credentials, DB passwords) in a GitHub Actions workflow?
intermediateTests whether you know to use encrypted repository secrets rather than hardcoding credentials into workflow files.
How do you implement a rollback strategy in your CI/CD pipeline if a deployment fails?
advancedTests whether you've actually planned for the failure path, not just the happy deploy path.
How do you deploy a Dockerized Spring Boot app to AWS ECS/EKS from a GitHub Actions pipeline?
advancedTests whether you can connect the build, push, and deploy stages into one working end-to-end pipeline.
What is the difference between blue-green deployment and rolling deployment in a CI/CD context?
advancedTests whether you know the tradeoff between instant-switch simplicity and gradual-rollout safety.
VPC & IAM
What is a VPC? What are its core components?
beginnerTests whether you know subnets, route tables, internet gateways, and NAT gateways as the building blocks of a VPC.
What is the difference between a Security Group and a Network ACL (NACL)?
beginnerTests whether you know one is stateful and instance-level while the other is stateless and subnet-level.
What is the difference between an IAM User, Group, Role, and Policy?
beginnerTests whether you know these four building blocks and how they combine to control access on AWS.
What is an STS AssumeRole? How does cross-account access work?
advancedTests whether you know how temporary credentials let a principal in one account securely act in another.
Databases (RDS, DynamoDB)
What is the difference between RDS Single-AZ and Multi-AZ?
beginnerTests whether you know Multi-AZ is for automatic failover, not read scaling — a very common point of confusion.
What is Amazon DynamoDB? When would you choose it over RDS?
beginnerTests whether you know when predictable low-latency NoSQL access patterns beat relational flexibility.
What is DynamoDB Partition Key vs Sort Key?
intermediateTests whether you know how DynamoDB physically distributes and orders data based on your key design.
How do you handle DynamoDB hot partition problem?
advancedTests whether you know how a poorly chosen partition key can bottleneck throughput even when overall capacity is fine.
Object Storage (S3/MinIO)
Why is storing uploaded files on the local server filesystem a bad practice in production, and what should you use instead?
intermediateTests whether you know local storage breaks the moment you scale to multiple instances behind a load balancer.
What is a pre-signed URL? How does it allow temporary file access without exposing your S3 bucket publicly?
intermediateTests whether you know a signed, time-limited URL grants access without changing the bucket's actual permission policy.
How do you generate a pre-signed URL for S3 upload so the client uploads directly to S3, bypassing your server entirely?
advancedTests whether you know this pattern avoids routing large file bytes through your own application servers.
How do you implement multi-part upload for large files (over 100MB) in S3?
advancedTests whether you know large uploads are split into parallel chunks that can retry independently instead of restarting the whole upload.
What is MinIO, and why would you use it locally during development instead of connecting to real AWS S3?
intermediateTests whether you know MinIO's S3-compatible API lets you develop against object storage without any cloud dependency or cost.
How do you implement S3 lifecycle policies to automatically archive old files to Glacier?
advancedTests whether you know how to trade retrieval speed for storage cost automatically as data ages.
Lambda & Serverless
What is AWS Lambda? What are its key characteristics?
beginnerTests whether you know the basics of event-driven, pay-per-invocation serverless compute.
What is the Lambda execution model? What happens during a cold start?
beginnerTests whether you know why the first invocation after idle time is slower, and how provisioned concurrency addresses it.
What is AWS Step Functions? How does it orchestrate Lambda functions?
intermediateTests whether you know how to coordinate multiple Lambda functions with retries and branching instead of chaining them manually.
Messaging, Containers & DevOps
What is the difference between SQS and SNS?
beginnerTests whether you know one is a pull-based queue and the other a push-based pub/sub topic.
What is Amazon ECS? What is the difference between EC2 launch type and Fargate?
beginnerTests whether you know the tradeoff between managing your own EC2 capacity and letting AWS run containers serverlessly.
What is Amazon EKS? How does it differ from ECS?
beginnerTests whether you know EKS is managed Kubernetes while ECS is AWS's own simpler, non-portable orchestrator.
Database Optimization Techniques
How do you use EXPLAIN / EXPLAIN ANALYZE to find and fix a slow query?
intermediateTests whether you can actually read a query plan, not just know the command exists.
What is a composite index, and when does column order inside it actually matter?
advancedTests whether you know a composite index is only useful for queries that filter on its leftmost columns first.
Why should you always paginate large result sets, and what is keyset pagination?
advancedTests whether you know OFFSET-based pagination gets progressively slower on large tables, and keyset pagination avoids that.
Why is a batch insert/update faster than doing it row by row, and how do you batch it in JPA?
advancedTests whether you know each round trip has fixed overhead, and batching amortizes that cost across many rows.
What is a covering index and how does it eliminate table lookups entirely for a query?
advancedTests whether you know an index that already contains every selected column skips the extra trip to the actual table row.
How does a type mismatch in a WHERE clause silently kill index usage?
advancedTests whether you know an implicit conversion on the indexed column forces a full scan even though an index exists.
When is denormalization actually better than normalization for performance?
advancedTests whether you know read-heavy systems can trade some redundancy for avoiding expensive joins at query time.
How do soft deletes (an is_deleted flag) hurt performance over time, and how do you mitigate it?
advancedTests whether you know a growing pile of never-really-deleted rows bloats indexes and slows every query that scans the table.
How do you archive historical data to keep the working table small and fast?
advancedTests whether you know moving cold data to a separate archive table keeps hot-path queries fast on the active table.
How do read replicas reduce load on the primary database, and what consistency tradeoff do they introduce?
intermediateTests whether you know replicas offload read traffic at the cost of potential replication lag on reads.
Security & Networking
What is AWS KMS (Key Management Service)? What are CMKs?
beginnerTests whether you know the basics of how AWS manages encryption keys used across its services.
What is AWS WAF? What attacks does it protect against?
intermediateTests whether you know WAF filters application-layer attacks like SQL injection and XSS at the edge, before they reach your app.
Docker Fundamentals
What is Docker? What problem does it solve compared to traditional deployment?
beginnerTests whether you know Docker solves the 'works on my machine' environment-consistency problem specifically.
What is a container? How does it differ from a Virtual Machine (VM)?
beginnerTests whether you know containers share the host OS kernel while VMs each run their own full OS.
What is the difference between a Docker image and a Docker container?
beginnerTests whether you know an image is an immutable blueprint while a container is a running (or stopped) instance of it.
Dockerfile & Images
What is a Dockerfile? What is it used for?
beginnerTests whether you know a Dockerfile is a reproducible, version-controlled recipe for building an image.
What is the difference between CMD and ENTRYPOINT? How do they interact?
intermediateTests whether you know how these two instructions combine, and which one CLI arguments actually override.
What is a multi-stage build in Docker? Why is it used?
intermediateTests whether you know how to keep build tools out of your final image to drastically shrink its size.
What is Docker layer caching? How do you structure a Dockerfile to maximize cache hits?
intermediateTests whether you know to order instructions from least to most frequently changing for faster rebuilds.
AWS Comparisons
EC2 vs Lambda — when would you choose each?
intermediateTests whether you know the always-on-control versus event-driven-simplicity tradeoff between the two.
ECS vs EKS — what's the real difference for container orchestration on AWS?
intermediateTests whether you know one is AWS-native and simpler, the other is portable standard Kubernetes with more operational surface.
S3 vs EBS vs EFS — object storage vs block storage vs file storage, when do you use each?
intermediateTests whether you know these three solve fundamentally different storage access patterns, not just 'different AWS storage products.'
RDS vs DynamoDB — relational vs NoSQL, when do you choose which on AWS?
intermediateTests whether you know this is really an access-pattern-and-scale question, not just a technology preference.
ALB vs NLB vs CLB (Classic Load Balancer) — Layer 7 vs Layer 4, when do you choose which?
intermediateTests whether you know which layer each operates at and what capability that gives or takes away.
SQS vs SNS vs EventBridge — queue vs pub/sub vs event routing, how do these three actually differ?
intermediateTests whether you know the messaging pattern each is purpose-built for, not just that they're all 'AWS messaging.'
IAM User vs IAM Role — permanent vs temporary credentials, when does each apply?
intermediateTests whether you know why AWS itself recommends roles over long-lived user credentials wherever possible.
Containers & Networking
What are the Docker network types? (bridge, host, none, overlay, macvlan)
beginnerTests whether you know the different ways a container can (or can't) talk to the host and other containers.
How do you limit CPU and memory for a Docker container?
intermediateTests whether you know how to prevent one noisy container from starving every other container on the same host.
Volumes & Compose
What is the difference between a Docker volume and a bind mount?
beginnerTests whether you know Docker manages one for you while the other points at an arbitrary host filesystem path.
What is Docker Compose? What is it used for?
beginnerTests whether you know how to define and run a multi-container application from a single YAML file.
What is a health check in Docker Compose? How does it work?
intermediateTests whether you know how Compose determines a container is actually ready, not just started.
Security & Production
What are the main security risks of running containers as root?
intermediateTests whether you know why a container breakout is far more dangerous when the process inside is running as root.
How do you run a Docker container as a non-root user?
intermediateTests whether you know how to configure a Dockerfile's USER instruction correctly for production hardening.
Kubernetes & Container Orchestration
How does Kubernetes HorizontalPodAutoscaler work, and what metrics can trigger scaling?
advancedTests whether you know HPA can scale on more than just CPU — custom and external metrics too.
What is the difference between ConfigMap and Secret in Kubernetes?
intermediateTests whether you know Secrets are only base64-encoded by default, not encrypted, and what that implies for real security.
What is the sidecar container pattern in Kubernetes and when do you use it?
advancedTests whether you know a helper container can extend a pod's behavior (logging, proxying) without touching the main app's code.
How do you optimize a Docker image's size for a Spring Boot application?
intermediateTests whether you know multi-stage builds, slim base images, and layer ordering all contribute to a smaller final image.
Docker Internals & Swarm
What are cgroups (control groups)? How does Docker use them for resource limits?
intermediateTests whether you understand the actual Linux kernel mechanism Docker relies on to enforce CPU/memory limits.
When would you choose Docker Swarm over Kubernetes?
intermediateTests whether you know Swarm's simplicity-versus-ecosystem tradeoff against Kubernetes for smaller, simpler deployments.