Backend

Beginner backend engineering: the life of an HTTP request, methods, status codes, headers, cookies and CORS, a runnable HTTP server, layered application structure, configuration and the twelve-factor app, data access, validation and errors, logging, and concurrency models.

The two most common backend stacks: the Node.js runtime, event loop, worker threads and frameworks (Express, Fastify, NestJS), and Java Spring Boot 4 with dependency injection, MVC, JPA, @Transactional pitfalls and virtual threads. Runnable demos included.

Designing HTTP APIs that last: REST resource modeling, status codes, idempotency keys, conditional requests, cursor pagination, versioning, RFC 9457 problem details, long-running operations, GraphQL and DataLoader, gRPC, and webhooks with signatures. Runnable demos included.

Backend security from beginner to advanced: sessions vs tokens, password hashing, JWT pitfalls, OAuth 2.0 and 2.1 with PKCE, OIDC, MFA with TOTP and passkeys, authorization models, and the OWASP Top 10:2025 with concrete defenses. Runnable demos included.

Backend performance: measure first, profile, find where time goes, HTTP caching with ETag and 304, application caches with single-flight stampede protection, DataLoader batching, concurrency limits, database access, payload size, Node and JVM tuning, and load testing. Demos executed.

Background work and messaging for backend engineers: when to go async, job queues, retries with backoff, idempotent consumers, dead-letter queues, the transactional outbox, event schemas, scheduling, webhooks delivery, and durable workflows. Runnable queue and outbox demos.

Backend architecture and testing: layered, hexagonal and clean architecture with a runnable Java example, DDD essentials, cross-cutting concerns, the testing pyramid, test doubles, Testcontainers, contract tests, and a runnable Node test-runner example with mocks.

Getting a backend into production and keeping it healthy: Docker images, docker compose, Kubernetes essentials, probes and graceful shutdown (with a runnable demo), configuration and secrets, CI/CD pipelines, serverless, infrastructure as code, and runtime observability.

Backend interview preparation: what each level is graded on, a 60-question bank with pointers, a worked REST API design exercise, coding round tasks mapped to runnable examples, a production debugging flowchart, cheat sheets, common mistakes, and study plans.