Table of Contents

• Examples — Month 6 (Production, Observability & Capstone)
• Week 1 — logging, metrics, tracing, health
• Week 2 — packaging, CI, config, shutdown
• Week 3 — profiling, allocations, optimization, rate limiting
• Week 4 — capstone architecture

Examples — Month 6 (Production, Observability & Capstone)

Standard-library-only programs that teach this month's observability concepts. The real production stack uses third-party libraries (prometheus/client_golang, go.opentelemetry.io/otel), but the concepts — structured records, trace propagation, probe semantics, request correlation — are reproducible with the stdlib, so these compile and run with nothing installed. Where a topic genuinely needs a third-party SDK (Prometheus client, OTel exporter), the day note shows the real API as a snippet instead.

Week 1 — logging, metrics, tracing, health

Topic	Run	Teaches	Day
slog	go run ./examples/month-06/slog	structured logging with log/slog: JSON/Text handlers, levels, typed attrs, With/WithGroup, SetDefault, ReplaceAttr redaction	141
tracecontext	go run ./examples/month-06/tracecontext	W3C Trace Context traceparent: trace-id vs span-id, parent/child hops, sampling flag, strict parsing	143
healthcheck	go run ./examples/month-06/healthcheck	liveness vs readiness vs shutdown: /healthz ignores deps, /readyz aggregates them and drains on shutdown	144
correlation	go run ./examples/month-06/correlation	correlation IDs end to end: middleware extract-or-mint, context propagation, a context-reading slog.Handler	145

Day 142 (Prometheus client_golang) and Day 143's OpenTelemetry SDK need third-party libraries, so their real APIs live as snippets in the day notes; the stdlib tracecontext example covers the propagation format that ties traces together.

Week 2 — packaging, CI, config, shutdown

Topic	Run	Teaches	Day
buildinfo	go run ./examples/month-06/buildinfo	version stamping: runtime/debug.ReadBuildInfo + an ldflags-overridden var (VCS revision, deps)	148
config	go run ./examples/month-06/config	12-factor config: typed env parse, defaults, accumulate-and-errors.Join validation, fail-fast	152
secrets	go run ./examples/month-06/secrets	*_FILE-first secret resolution (Docker/K8s pattern) + redaction for safe logging	152
graceful	go run ./examples/month-06/graceful (Ctrl-C)	signal-driven graceful HTTP shutdown: signal.NotifyContext + srv.Shutdown(ctx) draining in-flight requests	153

Docker multi-stage builds, docker compose, distroless hardening, and GitHub Actions (Days 148–151) are tooling/config, not Go code — their Dockerfile, compose.yaml, and ci.yml snippets live inline in the day notes.

Week 3 — profiling, allocations, optimization, rate limiting

Topic	Run	Teaches	Day
pprof	go run ./examples/month-06/pprof	collect CPU & heap profiles with runtime/pprof; the net/http/pprof endpoint for live services; what go tool pprof reads	155
escape	go run ./examples/month-06/escape	escape analysis: stack vs heap, measuring with testing.AllocsPerRun, seeing the compiler's decision via -gcflags=-m	156
syncpool	go run ./examples/month-06/syncpool	sync.Pool to reuse allocations on a hot path; Reset-after-Get discipline; GC-may-drain caveats	157
ratelimit	go run ./examples/month-06/ratelimit	token-bucket rate limiter from scratch; burst vs rate; HTTP middleware + 429/Retry-After shape	160

Load testing (k6 / vegeta, Day 158), govulncheck/gosec (Day 159), and the AuthN/Z hardening on Day 160 are CLI tools and HTTP middleware whose real APIs live inline in the day notes (k6 is JS, vegeta/govulncheck/gosec are external commands). The stdlib ratelimit example covers the rate-limiting algorithm itself.

Week 4 — capstone architecture

Topic	Run	Teaches	Day
architecture	go run ./examples/month-06/architecture	ports & adapters / dependency inversion: a Service depending on a Repository interface, with an in-memory adapter swappable for Postgres; sentinel wrapping with %w	162
restapi	go run ./examples/month-06/restapi	the REST transport layer with Go 1.22 net/http method+wildcard routing (POST /links, GET /links/{code}), JSON DTOs, DisallowUnknownFields, driven by an in-process httptest.Server	163
cacheaside	go run ./examples/month-06/cacheaside	the cache-aside read path (the Redis layer's concept) as a bounded LRU + TTL cache built from container/list + sync.Mutex, with a GetOrLoad loader	164

The capstone's gRPC API, Postgres (pgx) persistence, Redis cache, Prometheus metrics, and OpenTelemetry tracing need third-party SDKs, so their real APIs live as snippets in the Day 162–167 notes; these stdlib programs teach the underlying shapes (layering, routing, cache-aside) those libraries plug into.

Every program imports only the standard library.