50 Cloud & DevOps Interview Questions and Answers (2026)

#devops #aws #docker #webdev

Cloud and DevOps knowledge is no longer optional for backend engineers. AWS Lambda, Docker, and microservices show up in job requirements for roles that used to be purely application-focused. Azure Entra ID is now a standard topic for any role touching enterprise Microsoft environments.

This guide covers 50 questions across 6 categories, written to be said out loud in an interview: specific, grounded in real behavior, with working code examples throughout.

Full article with all answers, code snippets, and a quick reference table:
devencyclopedia.com/blog/cloud-devops-interview-questions

What's covered

Category 1: Serverless & AWS Lambda (Q1–Q8)

What is serverless and what problem does it solve?
How does the Lambda execution model work?
Lambda cold starts and how to reduce them (provisioned concurrency, SnapStart, runtime choice)
Reserved vs unreserved vs provisioned concurrency
Lambda Layers, invocation types, limits, and production monitoring

Category 2: AWS API Gateway (Q9–Q14)

REST API vs HTTP API vs WebSocket API
Integration types: Lambda proxy, HTTP, AWS Service, Mock
Authorization: IAM, Lambda Authorizer, JWT Authorizer
Throttling, stages, canary deployments

Category 3: AWS S3 (Q15–Q20)

Core concepts: buckets, objects, keys
Storage classes: Standard, IA, Glacier, Intelligent-Tiering, Deep Archive
Versioning, presigned URLs (GET and PUT), event notifications
Bucket policy vs ACL

Category 4: Docker (Q21–Q32)

Docker vs VM: shared kernel, boot time, resource overhead
Image vs container, layer caching, efficient Dockerfiles
Multi-stage builds (fat build image vs lean production image)
Compose, network drivers, volumes vs bind mounts
Container security: non-root, distroless, cap-drop, read-only FS
Docker Swarm vs Kubernetes

Category 5: Microservices (Q33–Q42)

Monolith vs microservices: when to use each
Synchronous (REST, gRPC) vs async (queues, Kafka) communication
Circuit Breaker pattern (Closed, Open, Half-Open states)
Saga pattern: choreography vs orchestration
Event sourcing, distributed tracing, service mesh, 12-factor app

Category 6: Azure Entra ID (Q43–Q50)

What Entra ID is and how it differs from on-premises AD
App Registration vs Service Principal
OAuth 2.0 flows: Auth Code, PKCE, Client Credentials, OBO, Device Code
Managed Identities (why they replace client secrets)
Conditional Access, Azure RBAC vs Entra ID roles, SSO, PIM

Quick sample: Q29 — Multi-stage Docker build

# Stage 1: build
FROM node:22 AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build

# Stage 2: production image
FROM node:22-alpine AS production
WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production
COPY --from=builder /app/dist ./dist
USER node
EXPOSE 3000
CMD ["node", "dist/server.js"]

The production image contains only the Alpine runtime, production deps, and compiled output. The build environment is discarded. Result: ~80MB instead of ~800MB.

Quick sample: Q36 — Circuit Breaker (Node.js)

const CircuitBreaker = require("opossum");

const breaker = new CircuitBreaker(callPaymentService, {
  timeout: 3000,
  errorThresholdPercentage: 50,
  resetTimeout: 30000,
});

breaker.fallback(() => ({ status: "deferred", message: "Payment queued for retry" }));
breaker.on("open", () => logger.warn("Circuit OPEN"));

const result = await breaker.fire(paymentData);