Go SRE Interview Gym

A monorepo of hands-on exercises covering what actually gets asked in Go live-coding rounds for SRE roles. Each numbered folder is self-contained:

• main.go — the assignment (in comments) + a scaffold with TODOs and a small runnable demo
• main_test.go — the interviewer: tests that define "correct", including the traps (goroutine leaks, races, boundary conditions)
• README.md — the deep dive: why the idiom exists, what breaks in production, and the follow-up questions interviewers reach for

Setup

Go ≥ 1.22 required (loop-variable semantics), any recent toolchain is fine — built and verified against go 1.27. Pure stdlib, zero dependencies.

Workflow

# pick an exercise, read the assignment in main.go, implement the TODOs
go test -race ./01-url-health-checker/     # -race ALWAYS. non-negotiable.

# run everything you've solved so far
go test -race ./...

# some exercises have benchmarks worth exploring
go test -bench=. -cpu=1,4,8 ./09-safe-counter/

Interview-realistic rules: timer set to 30 min, no autocomplete, no LSP if you're brave, and narrate your reasoning out loud — the talking is graded as much as the code.

The ladder

#	Exercise	Core skill	Freq in interviews
01	url-health-checker	bounded concurrency, ctx, HTTP hygiene	★★★★★
02	worker-pool	channel closing protocol, WaitGroup	★★★★★
03	rate-limiter	lazy state, mutex, monotonic time	★★★★☆
04	log-topn	streaming, Scanner limits, map→sort	★★★★☆
05	lru-cache	map+list composite, O(1) design	★★★★☆
06	retry-backoff	jitter, ctx-aware sleep, error classes	★★★☆☆
07	fan-in	leak-free cancellation, nil-channel trick	★★★☆☆
08	graceful-shutdown	signals, Shutdown ctx inversion, k8s	★★★☆☆
09	safe-counter	mutex vs atomic vs sharding, -race	★★★★☆ (as warm-up)
10	gotchas	"what does this print" trivia round	★★★★★

Suggested order: 09 → 02 → 01 → 03 → 05 → 04 → 06 → 07 → 08, with gotchas (10) sprinkled daily. 09 first because it calibrates you on -race; 01/02 are the highest-yield; 08 is the best conversation generator in on-sites.

Ground rules baked into the tests

• Tests use timeouts to catch deadlocks and missing close() — a hanging test is a failing test with extra steps.
• Several tests count goroutines or track peak concurrency with atomics — read them after solving; test-writing techniques are interview material too.
• Everything must pass under -race. A green test that fails -race is red.

Note on the gotchas folder

10-gotchas/* are predict-then-run programs: ex02 deadlocks on purpose, ex11 doesn't compile on purpose. Run them individually (go run ./10-gotchas/ex01-loopvar/), not as part of go build ./.... Answers are collapsed in 10-gotchas/README.md.