Debug false-ready and dependency outages

Map failure classes for GET /readyz: retryable vs fatal vs needs-human. Retries need budgets, jitter, and idempotency rules aligned to readyz fails if index digest ≠ pinned digest; rollback restores previous digest in < 2 min. The chapter’s signature failure — new pods serve empty index while old pods terminate — citation miss spike — must take a deliberate branch, not a generic catch-all.

Implement the degrade/rollback/refuse behavior platform engineer shipping faq-index@sha256:a1b2 to staging needs when DEPLOY-EMPTY-INDEX-5 repeats. Prefer scoped controls (one flag, one weight, one tenant, one secret version) over fleet-wide restarts. Preserve evidence; do not delete logs to “clean the demo.”

After containment, check ready_ratio == 1 and citation_miss_rate ≤ 0.02 during rollout moves in the safe direction and watch for retry amplification. Write the stop condition that ends the incident response for this lab.

Chaos note: inject only one fault class at a time and restore fixtures after. Watch for dual failures — dependency down and retry amplifier — which is how new pods serve empty index while old pods terminate — citation miss spike becomes an outage. Customer communication templates (even if only for the drill) beat silence. If you queue deferred work, define poison-message handling. Budget documents should state the maximum extra spend allowed during retries. Close the loop by linking the containment action to a dashboard panel for ready_ratio == 1 and citation_miss_rate ≤ 0.02 during rollout.

Draw a state diagram for degrade modes and put it in the repo as ASCII if needed. Cap concurrent retries across the process, not only per request. Ensure cancellation propagates to downstream HTTP clients. When failing closed, choose a user-visible message that does not leak internals. Practice the single command that flips the kill switch or weight to zero. After recovery, drain or inspect deferred work before declaring green. In this chapter the product is containerized café FAQ RAG with readiness probes and versioned index pin, the human stakeholder is platform engineer shipping faq-index@sha256:a1b2 to staging, and the incident id you design against is DEPLOY-EMPTY-INDEX-5. Re-state the oracle in your notes — kubectl rollout status shows ready; /readyz 200 only when index pin matches — and keep the invariant visible: readyz fails if index digest ≠ pinned digest; rollback restores previous digest in < 2 min. Track ready_ratio == 1 and citation_miss_rate ≤ 0.02 during rollout as the scoreboard. Surface under change control: GET /readyz. If you only have forty minutes, finish the fixture for new pods serve empty index while old pods terminate — citation miss spike before polishing UI. Promotion language stays ternary: promote, hold, or roll back based on evidence, not hope.