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.

How to use this Do one lesson, take its quiz from memory (no peeking), then skim the matching section of the cheat sheet. Come back a day later and re-take the quiz — spacing is what turns fluency into real retention. Stuck on anything? Ask me — I'm your teacher, not just the author.

Part 1 — Foundations available now

1 · What Kafka is & why it exists

The log, and pub/sub decoupling — told through your SendEmail flow.

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2 · Topics, partitions & offsets

The data model. Why partitions are the unit of ordering and parallelism.

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3 · Consumer groups & rebalancing

How work is split, how offsets are tracked, what happens when a consumer dies.

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Part 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.

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5 · Delivery semantics

At-most / at-least / exactly-once — and which our consumers get (strict vs AlwaysCommit()).

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6 · Idempotency & retries

At-least-once + our idempotentService ≈ exactly-once, without transactions.

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7 · Replication & ISR

Leaders, followers, and how Kafka survives a broker dying.

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8 · Retention vs compaction

Keeping data by age vs keeping the latest per key.

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Part 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.

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10 · The priority-lane pattern

Kafka has no message priority — so why two topics + two groups in one pod.

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11 · Failure modes & the missing DLQ

What happens when X fails — for every X — and the DLQ we don't have.

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Later / 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.
All 11 lessons are built — the full interview arc. The last mile is retrieval, not reading: ask me to run a mixed mock interview across every lesson, and where you're solid I'll record it so we both know it's locked in. Or go deeper on anything that didn't click.