Agentic coding Session 3 - Live Problem-Solving Under Pressure

"Design the backend for Twitter." Reciting HTTP verbs won't get you through that whiteboard session. In this deep dive we build a complete, staff-level blueprint for REST API design: the reasoning behind every rule, the trade-offs interviewers probe, and the patterns that keep large systems evolving safely.You'll learn:- Fielding's six REST constraints, and why statelessness unlocks horizontal scaling- The Richardson Maturity Model, from the "swamp of POX" to HATEOAS- URI design: stable identifiers, shallow nesting, filtering and sparse fieldsets- Safety and idempotency, PUT vs PATCH, and JSON Merge Patch vs JSON Patch- Status codes that show polish: 201 + Location, 409 Conflict, 410 Gone, 422- Offset vs cursor pagination- Versioning, breaking changes, tolerant readers and the expand-contract pattern- Deprecation headers, RFC 7807 problem details and trace IDs- OAuth 2.0, API keys, JWTs and mutual TLS- Rate limiting: fixed window, sliding log, token bucket and leaky bucket- ETags, Cache-Control, and 202 Accepted for long-running jobs- OpenAPI and consumer-driven contract testing with PactChapters00:00 The whiteboard challenge01:35 An API as a city02:20 Fielding's six constraints03:28 Code on demand04:38 Statelessness and scaling07:44 The layered system09:21 The Richardson Maturity Model12:29 HATEOAS and server-driven state15:13 Pragmatic hypermedia15:59 URI design rules17:30 Stable identifiers18:38 Nesting vs flattening20:12 Query parameters20:59 Safety and idempotency22:54 PUT vs PATCH25:39 JSON Merge Patch vs JSON Patch27:39 201, 202 and 20428:25 409 Conflict and optimistic locking30:19 410 Gone31:07 400 vs 42231:54 Response envelopes32:41 Offset pagination34:39 Cursor pagination36:11 API versioning38:55 Breaking vs non-breaking changes40:30 Tolerant readers41:40 The expand-contract pattern44:46 Deprecation and Sunset headers45:52 RFC 7807 problem details46:41 Trace IDs47:27 Never leak internals48:14 Returning all validation errors49:24 OAuth 2.0 and API keys51:25 JWTs and mutual TLS52:57 Rate-limiting algorithms56:29 429 and Retry-After57:15 ETags and Cache-Control1:01:11 Async jobs with 202 Accepted1:03:58 OpenAPI1:05:30 Consumer-driven contracts with Pact1:08:39 Recap: API design is empathy#RESTAPI #APIDesign #SystemDesign #BackendEngineering #SoftwareArchitecture #InterviewPrepInterview Prep Podcast

Your connection drops mid-checkout on a $1,000 ticket. Do you hit refresh and risk paying twice? The answer lives in the invisible architecture of REST APIs. In this deep dive we go from the basic grammar of the web to the patterns that keep global platforms fast, safe and reliable.You'll learn:- What REST really is, and why verbs never belong in your URLs- Resource naming, the two-level nesting rule, and when to flatten- Honest HTTP status codes and error responses with trace IDs- API versioning: URI vs headers vs content negotiation- Why offset pagination breaks at scale, and how cursors fix it- Safe vs idempotent methods, and how idempotency keys prevent double charges- Authentication vs authorization, OAuth 2.0, and the trade-offs of JWTs- ETags, sparse fieldsets, compression and 202 Accepted for long-running jobs- Rate-limit headers and the token bucket algorithm- The Richardson Maturity Model, HATEOAS, and API governance with OpenAPIChapters00:00 The $1,000 refresh dilemma00:45 "It works" vs "it's designed well"01:31 What REST really is02:17 Resources: nouns and verbs03:04 REST vs RPC03:52 Nesting and flattening resources05:28 Honest status codes06:16 The status code vocabulary08:36 Error responses that help you fix things10:10 API versioning strategies11:44 Why offset pagination breaks12:53 Cursor-based pagination14:03 Securing filters14:38 Safe and idempotent methods16:02 Idempotency keys16:50 Authentication vs authorization17:37 JWT trade-offs19:11 Caching with ETags20:22 Sparse fieldsets and compression21:08 Long-running jobs with 202 Accepted21:31 Rate-limit headers22:16 Rate-limiting algorithms23:28 The Richardson Maturity Model24:14 HATEOAS in theory and practice25:24 API governance26:35 Three golden rules27:22 Final thought#RESTAPI #APIDesign #BackendEngineering #SoftwareArchitecture #SystemDesign #InterviewPrepInterview Prep Podcast

"Walk me through what happens from kubectl apply to the first request hitting your container." It sounds like a warm-up question, but how you answer it can decide whether you land a senior or staff role. In this deep dive we trace a pod from creation to production and unpack the failure modes interviewers expect you to anticipate.You'll learn:- The full startup chain: API server, etcd, controllers, scheduler, kubelet and container runtime- Why init containers can't run in parallel, and why migrations belong in one for security- Startup, liveness and readiness probes, and the liveness trap that turns a 10-second database blip into an outage- Native sidecars in Kubernetes 1.29 (KEP-753) and the startup and shutdown races they fix- HashiCorp Vault: mutating webhook injection, TokenReview and system:auth-delegator, and dynamic database credentials- Zero trust with mTLS, SPIFFE identities and JWTs, plus the alg: none attack and audience checks- Service DNS, ndots:5, ClusterIP "phantom" IPs, iptables vs IPVS, and headless services for gRPC- Istio traps: DestinationRule ordering, empty AuthorizationPolicies and a stray YAML hyphen- Helm secrets, migration hooks, and a five-phase rollout for breaking API changes- A layered runbook for debugging intermittent 503sChapters00:00 Introduction00:22 What interviewers are really listening for01:31 From kubectl apply to "success"03:06 The scheduler and the kubelet04:18 Init containers05:26 Why migrations belong in an init container06:34 Startup, liveness and readiness probes08:09 The liveness probe thundering herd trap10:04 What a liveness probe should check10:53 Startup probes for slow-booting apps11:40 The sidecar startup and shutdown race12:52 Native sidecars in Kubernetes 1.2913:39 Vault injection with a mutating webhook14:48 Vault's init and sidecar agents15:34 Vault authentication and TokenReview16:43 Dynamic database credentials17:55 A Postgres quoting trap18:44 Zero trust and mutual TLS19:52 SPIFFE identities in Istio policies20:17 mTLS vs JWT20:39 Istio policy traps21:46 The alg: none attack and audience checks23:20 Service DNS and the phantom ClusterIP24:31 iptables vs IPVS and headless services25:41 Istio routing and deployment order26:29 The YAML hyphen trap26:53 Helm versions and secrets27:41 Helm migration hooks28:04 Five phases for a breaking API change29:14 Debugging 503s step by step30:00 Matching symptoms to causes30:47 Final thought: abstractions leak#Kubernetes #DevOps #SRE #CloudNative #Istio #SystemDesign #InterviewPrepInterview Prep Podcast

Senior system design interviews don't test whether you know what a load balancer is. They test how you think under pressure: how you handle ambiguity, weigh brutal trade-offs and defend every box you draw. In this deep dive we unpack the framework used to evaluate senior engineers, architects and principal candidates.You'll learn:- The RADIO framework (Requirements, API, Data model, Infrastructure, Optimize) and how to split your 45 minutes- The one question that instantly signals seniority- REST vs gRPC, API versioning, and why offset pagination breaks at scale- Choosing a database by access pattern, and justifying every component with the NFRs- Why skipping non-functional requirements is the number one reason senior candidates fail- Peak vs average TPS, P99 tail latency, latency budgets, RPO and RTO, and compliance- Sticky sessions, sharding, hot shards, read replicas, CQRS and event streaming- The math of the nines, active-active vs active-passive, circuit breakers, bulkheads and graceful degradation- Exponential backoff with jitter to survive the thundering herd- The CAP theorem, the consistency spectrum, and why banks must choose CP to prevent double spendingChapters00:00 Introduction00:49 They test judgement, not definitions02:22 The roadmap03:36 The RADIO framework04:47 Requirements in five minutes06:00 The seniority signal06:47 API design and versioning08:20 Offset vs cursor pagination09:05 Choosing the data model10:18 Justifying infrastructure with NFRs11:28 Network boundaries11:50 Attacking your own design12:39 Observability and cost14:37 The URL shortener trap15:23 The NFR cheat sheet15:46 Peak vs average traffic16:33 Tail latency and fan-out17:44 Latency budgets19:16 RPO and RTO20:02 Compliance: GDPR, PCI DSS, SOX21:37 Scaling out and sticky sessions23:13 Sharding and the hot shard24:49 Cross-shard query trade-offs25:58 Read replicas and replication lag27:08 CQRS28:41 Event streaming and idempotency31:02 The nines of availability33:04 Active-active vs active-passive34:37 Circuit breakers36:09 Bulkheads37:18 Graceful degradation38:26 Thundering herd, backoff and jitter40:25 The CAP theorem43:09 The consistency spectrum45:32 The FinTech exception: double spending47:05 Why a rejected transaction beats a duplicate48:13 Recap: every design is a trade-off49:23 Final thought#SystemDesign #SoftwareEngineering #DistributedSystems #InterviewPrep #TechInterviews #SoftwareArchitectureInterview Prep Podcast

A single misconfigured setting in Kafka doesn't just slow a page down. It can silently vaporize financial transactions. In this deep dive we walk through real production failure scenarios and the exact reasoning interviewers look for in staff-level system design interviews.You'll learn:- Why acks=1 loses data, and the four configuration layers for zero data loss- Consistency vs availability: why a healthy cluster refuses writes on purpose- Pushing from 400,000 to 2 million events/s with batching, linger.ms and compression- How retries reorder a debit and a credit, and how idempotent producers fix it- Rebalance storms, cooperative sticky assignment and static membership- Hot partitions and the irreducible trade-off between ordering and scale- How deleting and recreating a topic silently skips hours of data- A 3 AM role-play: 85 under-replicated partitions, a disk at 96%, and why you never restart the broker- Exactly-once with Kafka transactions, and exactly-once into PostgreSQL- Tiered retry topics and dead letter queues- Split brain, KRaft quorums and vanishing tombstones- System design at scale: multi-tenant topics, quotas, event-driven sagas and change data capture with DebeziumIdeal for backend and platform engineers preparing for senior and staff-level interviews.Chapters00:00 Distributed systems have no X-ray01:08 Why Kafka interviews matter02:19 acks=1 and the 200 missing payments03:27 Four layers of zero data loss05:21 The CAP theorem trade-off06:31 Throughput: taxis vs buses07:42 batch.size, linger.ms and compression09:38 When retries reorder messages11:38 Idempotent producers12:48 Message keys and partition ordering13:12 Flash sale: buffer exhausted14:22 Decoupling with a local buffer and circuit breaker16:18 Rebalance storms18:13 Eager vs cooperative sticky rebalancing19:25 Static group membership20:12 Hot partitions and the hot key problem23:18 Silent data loss after recreating a topic25:20 auto.offset.reset and topic versioning26:08 3 AM: 85 under-replicated partitions28:54 Why you never restart the broker29:42 Disk at 96%: the 15-minute response31:36 Throttled reassignment, Cruise Control, tiered storage33:36 Duplicates in consume-transform-produce34:47 Kafka transactions37:11 Exactly-once into PostgreSQL39:56 Head-of-line blocking from retries41:08 Tiered retry topics and DLQs42:42 Split brain44:38 KRaft and quorum math45:27 Log compaction tombstones48:33 Multi-tenant topic design50:07 Tenant tiers and client quotas51:40 Event-driven sagas53:15 Compensating transactions54:51 Change data capture with Debezium57:13 Recap58:46 Will offsets still matter in five years?#Kafka #SystemDesign #DistributedSystems #SoftwareEngineering #InterviewPrep #BackendEngineeringInterview Prep Podcast

Why does a chat message arrive instantly, but the web was never built for it? In this deep dive we unpack WebSockets: how engineers turned a request/response web into an open, two-way line, and what that costs at scale.You'll learn:- Why short polling, long polling and Server-Sent Events fall short (and the math behind 200,000 empty requests per second)- How the WebSocket handshake hides inside a normal HTTP request, and the "cryptographic high-five" that proves the server understood- Why clients mask every frame but servers never do, and the cache-poisoning attack it prevents- Half-open connections, idle timeouts and why heartbeats every 20–30 seconds keep sockets alive- Close code 1006, the "ghost code" every system design candidate should know- The real cost of state: 1 million connections × 20 KB = 20 GB of RAM before a single message- Gateways, pub/sub buses, the thundering herd, and exponential backoff with full jitter- Cross-site WebSocket hijacking, and why tokens never belong in the URL- When NOT to use WebSockets: SSE vs WebSockets vs gRPC- Head-of-line blocking and why QUIC and WebTransport may be nextPerfect for software engineers preparing for system design interviews.Chapters00:00 Intro: the web wasn't built for real time02:19 Short polling and the 200,000 requests/second problem03:54 Long polling04:42 Server-Sent Events05:31 WebSockets and full-duplex communication06:19 The handshake: disguised as HTTP07:55 Sec-WebSocket-Accept: the cryptographic high-five09:05 Why clients mask frames09:53 Cache poisoning explained11:50 Half-open connections12:38 Idle timeouts at every network hop13:47 Heartbeats: Ping and Pong14:36 Close code 100615:23 The cost of state16:57 Scaling with gateways and pub/sub18:34 The thundering herd19:46 Exponential backoff with full jitter20:58 Cross-site WebSocket hijacking22:32 Ticket-based authentication23:45 When not to use WebSockets24:55 The big trade-off: latency vs statefulness25:43 Head-of-line blocking26:55 What's next: QUIC and WebTransport#SystemDesign #WebSockets #SoftwareEngineering #InterviewPrep #BackendEngineeringInterview Prep Podcast

The mental model and the toolkit come together here. We cover managing a session in real time — when to course-correct, when to clear and restart — the five failure patterns that quietly tank your work and how to fix each, and a complete worked problem run end to end: explore, plan, implement in a fresh session, verify with tests, and review with an adversarial subagent. Plus scaling techniques and exactly how to demonstrate competence when someone is watching you code.

This is where the deep technical interview questions live. Claude Code has five extension points — CLAUDE.md, skills, hooks, subagents, and MCP — and knowing which to reach for is a core competency. We break down each one: why CLAUDE.md is always-on context you must keep lean, how skills load knowledge on demand and why the description field decides everything, when hooks give you deterministic guarantees, how subagents isolate heavy work in their own context, and how MCP and CLI tools connect the outside world. Ends with the decision framework that ties them all together.

The Agentic Mental Model: what "agentic" means and the loop, the context window as the governing constraint, explore→plan→implement→commit, verification, and precise prompting.Most engineers meet AI coding tools as a smarter autocomplete. Claude Code is something else: an agent that explores, plans, and writes code on its own while you direct and review. This opening episode rewires how you think about the tool. We unpack what "agentic" actually means, why the context window is the one constraint that explains every best practice, the explore-plan-implement-commit workflow, and the discipline of verification — giving the agent a check it can run so it self-corrects. The foundation for everything that follows, and for any interview that asks how you think with an AI agent.

SEASON 1 — "The Shift"Listen to - S1E1 Interview an engineer who transitioned from backend → AI engineer. Their story IS the season premise.