{
  "assumption_density": 0.5,
  "assumptions": [
    "Valkey 7.2.x is API-compatible with the Redis commands and data structures currently used across the 200-node deployment — no custom Redis modules or RESP3-specific features that Valkey hasn't forked",
    "The existing deployment runs Redis 7.2 or earlier (last Apache-2.0 version) and has not yet upgraded to Redis 7.4+ under the new SSPL/RSAL license",
    "Cloud infrastructure can provision 20 additional nodes for canary without exceeding quota or budget approval timelines",
    "The 2M ops/sec workload is distributed across session cache, rate limiting, and pub/sub — not a single monolithic use case that cannot be decomposed for phased migration",
    "Envoy with redis_proxy filter can handle the dual-write throughput at the required proxy layer without becoming a bottleneck itself"
  ],
  "confidence": 0.82,
  "id": "5851eba9-8d79-4bab-9a09-6e2e22ae5b37",
  "next_action": "Deploy a 20-node Valkey 7.2.6 canary cluster in the same availability zone as the existing Redis deployment, configure Envoy with redis_proxy filter for dual-write from 10% of the production write path, and instrument Prometheus/Grafana dashboards tracking p99 latency, gossip bandwidth, pub/sub delivery latency, and node failure rate against the four abort thresholds.",
  "question": "should we replace Redis with Valkey now that Redis changed its license, or stay on Redis for a 200-node deployment handling 2M ops/sec?",
  "question_fit_score": 0,
  "rejected_alternatives": [
    {
      "path": "Hybrid architecture with Valkey at edge and commercial caching (ElastiCache) for critical workloads",
      "rationale": "Architecturally incoherent — ElastiCache IS Redis/Valkey under the hood. Introduced cache coherence problems at 2M ops/sec without naming a consistency protocol. Claimed p99 of 1.5ms while adding a synchronization layer, violating basic latency math. Fabricated budget constraints."
    },
    {
      "path": "Treat as a legal/contractual issue, negotiate commercial Redis license before any migration",
      "rationale": "SSPL/RSAL is a blanket license change, not negotiable per-customer. Redis Enterprise for 200 nodes would cost $400K-$600K/year vs. $50K one-time migration. Backup options (KeyDB unmaintained since 2022, DragonflyDB uses BSL 1.1) have the same or worse license problems. Delay accumulates unpatched CVE exposure on Redis 7.2."
    },
    {
      "path": "Reject dual-write as introducing insurmountable consistency risks and \u003e10ms p99 spikes",
      "rationale": "Overly pessimistic and unsupported by precedent. Envoy-based dual-write has been used successfully at scale (e.g., Pinterest's storage migrations). b003's abort thresholds directly address the latency concern with concrete rollback triggers."
    },
    {
      "path": "Explore technical feasibility of migration with focus on maintaining performance and 2-week rollback (b002)",
      "rationale": "Valid but strictly less specific than b003. b002 is essentially a weaker version of what b003 already provides with concrete phases, thresholds, and failure modes."
    }
  ],
  "reversal_conditions": [
    {
      "condition": "Valkey canary fails abort thresholds during Phase 1 (p99 \u003e3ms sustained, gossip \u003e100 Mbps, or \u003e2 node failures) and root cause is a fundamental Valkey architectural limitation rather than configuration",
      "flips_to": "Negotiate Redis Enterprise commercial license despite the $400K-$600K/year cost, or evaluate DragonflyDB if BSL 1.1 is legally acceptable for the organization"
    },
    {
      "condition": "Redis Ltd reverses the SSPL/RSAL license change or creates a permissive-use exemption for self-hosted non-competing deployments",
      "flips_to": "Stay on Redis, upgrade to latest version, cancel migration"
    },
    {
      "condition": "Pub/sub workload exceeds 100K messages/sec and cannot be isolated onto a dedicated cluster due to application coupling, causing cluster bandwidth saturation at scale",
      "flips_to": "Migrate session/rate-limiting to Valkey but move pub/sub workload to a dedicated message broker (Kafka, NATS) rather than running it on Valkey cluster"
    }
  ],
  "unresolved_uncertainty": [
    "Valkey 7.2.x cluster behavior at exactly 200 nodes is not widely benchmarked in public literature — the gossip bandwidth and rebalancing storm thresholds are engineering estimates, not production-validated numbers at this specific scale",
    "b003's budget of $50K is a rough estimate — actual costs depend heavily on cloud provider, instance types, and whether reserved/spot pricing is available for the canary phase",
    "The pub/sub 100K messages/sec threshold for bandwidth saturation is model-derived, not benchmarked against Valkey's specific cluster broadcast implementation",
    "Redis 7.2 security patch timeline is uncertain — Redis Ltd may continue critical CVE patches longer than expected, or may not",
    "b004 (killed) raised a valid concern about dual-write consistency during network partitions that b003 addresses only via abort thresholds, not via a formal consistency protocol"
  ],
  "url": "https://vectorcourt.com/v/5851eba9-8d79-4bab-9a09-6e2e22ae5b37",
  "verdict": "Execute a phased canary migration from Redis to Valkey 7.2.x over 4 months using a dual-write proxy pattern (Envoy with redis_proxy filter or Twemproxy). Phase 1: Stand up a 20-node Valkey canary (10% of fleet) receiving shadow writes while Redis serves all reads. Phase 2: Shift reads for session cache workload to Valkey canary, validating p99 ≤2ms and cache hit ratio ≥85%. Phase 3: Expand to 100 Valkey nodes at 50% traffic. Phase 4: Full 200-node cutover with Redis kept warm for 2-week rollback.\n\nAbort if: Valkey p99 exceeds 3ms, cluster gossip exceeds 100 Mbps, pub/sub latency exceeds 5ms, or more than 2 node failures in any 7-day canary window.\n\nKey failure mode: pub/sub at 200 nodes broadcasts to all cluster members — if real-time events exceed 100K messages/sec, internal bandwidth saturates. Mitigation: isolate pub/sub onto a dedicated 16-node cluster. Second failure mode: cluster rebalancing storms from 16,384 hash slots during node topology changes.\n\nBudget: $50K total. This avoids the $400K-$600K/year Redis Enterprise licensing cost and the security risk of staying on Redis 7.2 (last Apache-2.0 version) as patches shift to 7.4+.",
  "verdict_core": {
    "recommendation": "Execute a phased canary migration from Redis to Valkey 7.2.x using a dual-write proxy pattern over 4 months, with abort thresholds at p99 \u003e3ms, gossip bandwidth \u003e100 Mbps, pub/sub latency \u003e5ms, or \u003e2 node failures per 7-day window.",
    "mechanism": "Because a dual-write proxy (Envoy with redis_proxy filter) allows shadow writes to a 10% Valkey canary fleet while Redis continues serving all reads, enabling production-scale validation without risking the 2M ops/sec workload — and because phased traffic shifting (shadow writes → read shifting → 50% cutover → full migration) isolates each failure domain incrementally, with a 2-week warm Redis rollback window at every phase.",
    "tradeoffs": [
      "4-month migration timeline delays full license independence vs. a faster but riskier cutover",
      "$50K infrastructure and engineering cost for canary + proxy layer + scaling",
      "Operational complexity of running dual clusters and proxy layer during migration window"
    ],
    "failure_modes": [
      "PUB/SUB DIVERGENCE: At 200 nodes, pub/sub cluster-mode broadcast can saturate internal bandwidth if real-time events exceed 100K messages/sec, pushing p99 past 5ms. Mitigation: isolate pub/sub onto a dedicated 16-node Valkey cluster.",
      "CLUSTER REBALANCING STORMS: 16,384 hash slots across 200 nodes means adding/removing nodes triggers slot migration that can spike latency during rebalancing windows.",
      "Dual-write proxy introducing out-of-order writes during network partitions — mitigated by Envoy's connection pooling and b003's abort thresholds."
    ],
    "thresholds": [
      "p99 latency ≤2ms baseline, abort at \u003e3ms",
      "Cluster gossip bandwidth abort at \u003e100 Mbps aggregate",
      "Pub/sub message delivery latency abort at \u003e5ms",
      "Node failure abort at \u003e2 failures per 7-day window in canary",
      "Cache hit ratio must stay ≥85%",
      "Budget: $50K total ($15K canary, $10K proxy, $15K full scale, $10K contingency)"
    ]
  },
  "verdict_type": ""
}