Instrument metrics and rollout decisions

Instrument RAG API with complete green/v1 and blue/v2 stacks behind one router so release engineer flipping 100% router cut after green smoke can answer: demand, errors, latency/age, saturation. Emit fields needed by cutover_seconds and postcut_error_rate with bounded labels. Sample successful high-volume traces; keep errors and rollout transitions denser within policy.

Define at least one alert that would fire for BG-SCHEMA-ONESIDE-11, with a for/pending window that survives deploy blips. Missing scrape or missing revision labels must not look like health. Include a trace/log example id format you will actually search.

Add a unit/integration check that metrics increment on the happy path and on the schema migration applied only on blue — green rollback serves 500s branch. Store machine-readable output in CI artifacts when practical.

Cardinality discipline: tenant and revision are usually enough; raw question text is not a label. Exemplars or trace links beat screenshots alone when debugging BG-SCHEMA-ONESIDE-11. Define who owns alert fatigue review. If you export to a vendor, record retention and access. Synthetic probes should use non-sensitive fixtures and still exercise router → green|blue /v1/rag/answer. Practice the query you will type at 2am once, while calm.

Document the exact PromQL or log query in the runbook stub for this service. Verify histograms have buckets around your SLO target. Add a canary synthetic check that exercises the oracle path every few minutes in staging. Confirm that PII redaction happens before export. Track build/version as a label on the golden signals. Delete noisy debug logs before they become accidental product dependencies. In this chapter the product is RAG API with complete green/v1 and blue/v2 stacks behind one router, the human stakeholder is release engineer flipping 100% router cut after green smoke, and the incident id you design against is BG-SCHEMA-ONESIDE-11. Re-state the oracle in your notes — cutover < 30s; rollback restores green with zero dual-write divergence — and keep the invariant visible: blue must pass smoke + /readyz before cut; old green kept warm for 30m rollback. Track cutover_seconds and postcut_error_rate as the scoreboard. Surface under change control: router → green|blue /v1/rag/answer. If you only have forty minutes, finish the fixture for schema migration applied only on blue — green rollback serves 500s before polishing UI. Promotion language stays ternary: promote, hold, or roll back based on evidence, not hope.

Set a timer for twelve minutes and attempt only the observability concerns for Blue-green deploy lab. Speak aloud what release engineer flipping 100% router cut after green smoke would see on success versus on schema migration applied only on blue — green rollback serves 500s. Write three bullet artifacts you must keep: a fixture name tied to BG-SCHEMA-ONESIDE-11, a metric query for cutover_seconds and postcut_error_rate, and the rollback or refuse command for router → green|blue /v1/rag/answer. Then extend the notes with one sentence on how blue must pass smoke + /readyz before cut; old green kept warm for 30m rollback would be violated if you skipped this page. Close by restating the oracle in your own words without looking: cutover < 30s; rollback restores green with zero dual-write divergence.