Phase 07 — Production Systems: Consensus, Partitioning, and Build Modularity

Track: PMC Apache Committer Engineer
Phase: 07 of 12
Prerequisites: Phases 01–06 (code quality, review culture, patch workflow)

Why This Phase

A senior Apache committer is expected to reason about three categories of production system problems:

Consensus — how distributed nodes agree on a leader when any node can fail at any time
Partitioning — how data is mapped to shards deterministically and fairly across a consumer group
Build modularity — how large codebases are split into independently-testable, deployable modules

Each lab in this phase gives you a working Java implementation of the core algorithm, not just a description of it.

Lab	Topic	Artifact	Command
Lab 01 — Raft Leader Election	Raft consensus, terms, votes, heartbeats	`RaftCluster.java` simulation	`mvn test`
Lab 02 — Kafka Partitioning	murmur2 hash, round-robin, range assignment	`MurmurPartitioner.java`, `RangeAssignor.java`	`mvn test`
Lab 03 — Multi-module Maven	Parent POM, BOM, module dependency graph	`queue-api` / `queue-core` / `queue-app`	`mvn verify` (from parent)

Concept	One-line definition
Raft term	Logical clock that increments on each election attempt
Majority quorum	`floor(N/2) + 1` nodes must agree for any decision to commit
Election timeout	Random delay before a follower promotes itself to candidate
murmur2	Non-cryptographic hash used by Kafka to assign keys to partitions
Range assignment	Kafka's default consumer group partitioning: first N consumers get an extra partition if not evenly divisible
Reactor build	Maven builds all modules in dependency order in a single `mvn` invocation
`dependencyManagement`	Parent POM section that pins versions; child modules inherit them without specifying version
BOM	Bill of Materials — a `pom` with only `dependencyManagement`, imported by other projects

Raft election simulation: mvn test passes all 5 tests in RaftElectionTest
Kafka partitioning: mvn test passes all 8 tests in PartitionerTest
Multi-module build: mvn verify from the parent dir builds and tests all 3 modules
Written answers to at least 3 interview questions from the Hitchhiker's Guide

Company type	What they ask
Apache project PMC	"Walk me through what happens when a Kafka broker fails"
Distributed systems team	"How does Raft prevent two leaders in the same term?"
Platform/infra team	"How do you share a dependency version across 20 Maven modules without copy-paste?"
Data engineering	"Why does Kafka use murmur2 instead of Java's `hashCode()`?"