> cs·fundamentals
interview 0% an interactive refresher
02 [J][A][I] Stage 1

Backend Engineering

HTTP, API design, auth, architecture patterns, concurrency, messaging, distributed systems, and caching.

chapters
8
objectives
33
core
15
est. time
3h 21m
  1. 01
    2.1 HTTP/HTTPS deeply ★ core

    Methods + their safe/idempotent semantics, status-code families, the headers that matter, and what TLS adds.

    5 objectives · 2 readings · 25m
  2. 02
    2.2 API design & alternatives ★ core

    REST principles and when to choose REST vs GraphQL vs gRPC vs WebSockets, plus versioning, pagination, rate limiting, and idempotency keys.

    3 objectives · 2 readings · 28m
  3. 03
    2.3 Auth & security concepts ★ core

    Authentication vs authorization, sessions+cookies vs JWT, and OAuth2 vs OIDC — distinct jobs that interviewers love to conflate.

    4 objectives · 2 readings · 24m
  4. 04
    2.4 Application architecture & patterns

    Middleware, MVC/layered + DI, the SOLID principles (one “smell it fixes” each), and the practical design patterns worth recognizing.

    4 objectives · 1 readings · 30m
  5. 05
    2.5 Concurrency & parallelism

    Concurrency vs parallelism, threads vs processes vs async I/O, and the hazards (races, deadlocks) plus locks/mutexes vs semaphores.

    3 objectives · 22m
  6. 06
    2.6 Messaging & event-driven architecture

    Queues and pub/sub (Kafka, RabbitMQ, SQS), why at-least-once delivery forces idempotent consumers, and event-driven vs request/response tradeoffs.

    4 objectives · 1 readings · 22m
  7. 07
    2.7 Distributed systems & scaling ★ core

    Monolith vs microservices, API gateway/service discovery, CAP (CP vs AP and its scalability caveat), eventual consistency, and horizontal vs vertical scaling.

    6 objectives · 3 readings · 28m
  8. 08
    2.8 Caching ★ core

    Cache-aside vs write-through vs write-back, eviction policies (LRU/LFU/FIFO/TTL), where caches live, and Redis vs Memcached.

    4 objectives · 1 readings · 22m

Section assessment

Harder, multi-concept questions drawn from across the module. Aim for 75%.

section assessment12 questions · pass ≥ 75%
  1. 01hard

    Which pagination style is most stable when rows are being inserted between page requests?

  2. 02hard

    A mutex differs from a counting semaphore in that:

  3. 03hard

    During a network partition, a strongly-consistent (CP) store will:

  4. 04hard

    Write-back (write-behind) caching's main risk is:

  5. 05medium

    A request is well-formed but fails business validation. Best status code?

  6. 06medium

    Mobile clients over-fetch and make many round-trips. Which API style best addresses this?

  7. 07medium

    High-performance internal service-to-service calls with binary payloads and streaming favour:

  8. 08medium

    A key downside of stateless JWTs versus server sessions is:

  9. 09medium

    “Login with Google” on top of OAuth2 is provided by:

  10. 10medium

    You added a new payment type and had to edit a giant switch statement. Which SOLID principle did the design violate?

  11. 11medium

    Which pattern swaps an algorithm at runtime behind a common interface?

  12. 12medium

    Concurrency vs parallelism: