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Blue-Green Switchovers — OpsDeploy Guardrails

🧭 Quick Return to Map

You are in a sub-page of OpsDeploy.
To reorient, go back here:

Think of this page as a desk within a ward.
If you need the full triage and all prescriptions, return to the Emergency Room lobby.

A safe pattern to switch 100% of traffic between two identical stacks (Blue = current live, Green = new). Use this when you need instant rollback, reproducible cutovers, and zero surprise from schema or index drift.

Open these first

When to use

  • Model or prompt upgrades where instant rollback is required.
  • Vector index rebuilds that must cut over atomically.
  • Config, secrets, or feature-flag rewires that risk drift by region.
  • Store or analyzer changes that can shift ΔS/coverage.

Acceptance targets

  • ΔS(question, retrieved) ≤ 0.45 on 3 paraphrases after cutover.
  • Coverage ≥ 0.70 on the gold set (same as pre-switch).
  • λ convergent across 2 seeds, no flip increase vs Blue.
  • p95 latency within +15% of Blue; error rate ≤ 0.5%.
  • Instant rollback path validated (≤ 2 minutes TTR).

Architecture sketch


Users → Ingress/Edge  ─┬─> Blue: vN  (baseline: INDEX\_HASH A, PROMPT\_VER N, MODEL\_VER X)
└─> Green: vN+1 (INDEX\_HASH B, PROMPT\_VER N+1, MODEL\_VER Y)
↑
cutover switch (DNS/Ingress/ALB alias, or queue consumer pointer)

All reads/writes and side effects must point at a single active arm. If you have background writers (indexers, ETL), fence them with versioned topics or leases.

60-second checklist for a switch

  1. Freeze non-idempotent jobs
    Pause consumers that create side effects. Verify dedupe fences.
    Open: idempotency_dedupe.md

  2. Verify invariants
    INDEX_HASH, EMBED_SCHEMA, RERANK_CONF, PROMPT_VER, MODEL_VER, secrets. Green must pass the rollout gate.

  3. Warm Green
    Run smoke on 20–40 gold questions. Check ΔS, coverage, λ, latency. Prime caches.

  4. Flip the pointer
    Change the single routing knob (DNS TTL short, Ingress weight 0→100, queue consumer group pointer, or index alias swap).

  5. Hold and watch
    15–30 minutes: ΔS drift, coverage, λ flip rate, p95 latency, 5xx, tool loops.

  6. Unfreeze jobs
    Resume writers with new INDEX_HASH and contracts.

Implementation patterns

Ingress/ALB alias swap (HTTP)

  • Prefer one logical hostname. Point it to Blue or Green behind the load balancer.
  • Keep health checks strict: readiness must include secrets, index presence, and a gold QA.

DNS switch

  • Only if you can run with TTL ≤ 30s and you accept brief split-brain during propagation.
  • Safer to switch at the load balancer or service mesh layer.

Index alias swap (Vector/RAG)

  • Build Green index offline. Validate with sampled ΔS/coverage.
  • Swap an atomic alias docs_live → docs_vB. Keep docs_vA for instant rollback.
  • If store lacks aliases, emulate with a config key in a single-writer KV and block multi-writer races.

Queue consumer cutover

  • Stop Blue consumers, start Green consumers with a new CONSUMER_VER.
  • For exactly-once, commit offsets only after idempotent fences pass.

Stop & rollback rules

  • Stop if ΔS p95 drift > 0.15 or coverage < 0.60 or λ flip rate > 0.20.
  • Stop if 5xx > 1% or tool loop detection triggers.
  • Roll back by flipping the same single pointer back to Blue (or alias back to docs_vA).
  • After rollback, open: debug_playbook.md.

Observability you must pin before switch

  • Version fields: INDEX_HASH, EMBED_SCHEMA, RERANK_CONF, PROMPT_VER, MODEL_VER.
  • ΔS(question,retrieved) and ΔS(retrieved,anchor).
  • Coverage and λ states for 3 paraphrases.
  • Latency p50/p95 per stage (retrieve, rerank, reason).
  • Side-effect counts and dedupe hits.

Kubernetes example (Service selector flip)

apiVersion: v1
kind: Service
metadata:
  name: wfgy-live
spec:
  selector:
    app: wfgy-green   # flip between wfgy-blue / wfgy-green
  ports:
    - port: 80
      targetPort: http
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: wfgy-green
spec:
  replicas: 4
  selector: { matchLabels: { app: wfgy-green } }
  template:
    metadata: { labels: { app: wfgy-green } }
    spec:
      containers:
        - name: api
          image: ghcr.io/org/wfgy:canary
          readinessProbe:
            httpGet: { path: /healthz/ready, port: http }
            initialDelaySeconds: 5
            periodSeconds: 5

Vector store alias swap (pseudo)

# build green index
index_build --input corpus_vB.json --out docs_vB --metric cosine
# validate
wfgy_eval --gold gold_40.json --index docs_vB --min-cov 0.70 --max-ds 0.45
# atomic alias cutover
vec alias update docs_live --to docs_vB
# rollback
vec alias update docs_live --to docs_vA

Common pitfalls

  • Two writers during cutover → double side effects. Use a single pointer and idempotency keys.
  • Cache poisoning from mixed arms. Invalidate by INDEX_HASH or include it in cache keys.
  • Region drift. Switch one region at a time or use global flags with audit hashes.
  • Hidden analyzer/tokenizer mismatch. Re-embed or rerank deterministically if ΔS stays high.

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