A course grounded in your services
Apache Kafka, from zero to interview-ready
Every concept anchored to real Kafka flows in conversationmgmt, notification & spike.
You're starting from zero and heading toward an interview. The plan below builds the concepts interviews actually test — the data model, consumer groups, delivery semantics, replication — and pins each one to code you already own, so an abstract idea lands on something familiar. Lessons are short: one win each. Read them in order.
Part 1 — Foundations available now
1 · What Kafka is & why it exists
The log, and pub/sub decoupling — told through your SendEmail flow.
2 · Topics, partitions & offsets
The data model. Why partitions are the unit of ordering and parallelism.
ready3 · Consumer groups & rebalancing
How work is split, how offsets are tracked, what happens when a consumer dies.
readyPart 2 — The reliability core available now
The heart of most Kafka interviews. Do them in order — each builds on the last.
4 · Producers, keys & acks
How a write becomes durable; why our producer uses RequireOne.
5 · Delivery semantics
At-most / at-least / exactly-once — and which our consumers get (strict vs AlwaysCommit()).
6 · Idempotency & retries
At-least-once + our idempotentService ≈ exactly-once, without transactions.
7 · Replication & ISR
Leaders, followers, and how Kafka survives a broker dying.
ready8 · Retention vs compaction
Keeping data by age vs keeping the latest per key.
readyPart 3 — Applied to your services available now
Synthesis: every earlier concept, composed in your real code. The interview payoff.
9 · Trace one event end-to-end
Produce → partition → group → handler → DB, through spike's email flow.
ready10 · The priority-lane pattern
Kafka has no message priority — so why two topics + two groups in one pod.
ready11 · Failure modes & the missing DLQ
What happens when X fails — for every X — and the DLQ we don't have.
readyPart 4 — Senior Kafka practice new
The senior stretch — partition strategy, lag and rebalance judgment, schema evolution, retry/DLQ design, design review, and interview-grade answers.
12 · Partition strategy & hotspots
Choose partition shape from workload, not from habit.
new13 · Rebalances, lag & backpressure
Read lag correctly and explain the real cost of unstable groups.
new14 · Schema evolution & contract safety
Keep JSON event changes safe when producer and consumer deploy apart.
new15 · Retries, retry topics & DLQ design
Design retry escalation and dead-letter behavior honestly.
new16 · Reviewing Kafka designs
Judge durability, liveness, ordering, and hidden trade-offs like a senior engineer.
new17 · Senior interview questions
High-signal Kafka questions with the right answer shape.
new18 · Mock senior interview pack
A retrieval-first mock round with scoring and strong answer points.
newLater / out of scope
Deliberately parked so they don't crowd the interview core: Kafka Streams & ksqlDB, Kafka Connect, and production cluster operations/tuning. We'll revisit if the mission shifts.
Reference shelf
Cheat sheet
Dense revision sheet + interview one-liners.
Glossary
The canonical vocabulary, opinionated.
Repo Kafka map
Ground truth: our topics, wrapper, semantics.
Resources
Trusted courses, docs, the free book, and senior Kafka design topics.
Senior backend playbook
The compressed version of the new senior part: hotspots, lag, contracts, retry/DLQ design, review judgment, and interview answers.