{
  "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,
  "evidence_boundary": {
    "observed_facts": [
      "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?"
    ],
    "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",
      "team size defaulted: standard team (5-10 engineers) (not_addressed)",
      "existing stack defaulted: greenfield assumed (not_addressed)",
      "connection pooler defaulted: not specified (not_addressed)",
      "current state defaulted: not specified (not_addressed)",
      "rollback plan defaulted: not specified (not_addressed)",
      "data volume defaulted: not specified (not_addressed)"
    ],
    "inferred_specifics": [
      "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+.",
      "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.",
      "b003 had the highest confidence (0.90) among surviving branches, survived 3 rounds of adversarial challenge including a direct attack on dual-write feasibility (b004, killed), and provided the most concrete architecture: named proxy technology (Envoy redis_proxy), specific phase timeline, quantified abort thresholds, named failure modes with mitigations, and a budget breakdown. b002 (0.70) was a strictly weaker version of the same recommendation without the specificity.",
      "Deploy 20-node Valkey 7.2.6 canary cluster with identical configuration to current Redis nodes (maxmemory policy, persistence settings, cluster-enabled yes)",
      "Configure Envoy proxy with redis_proxy filter for dual-write, routing 10% of write traffic to Valkey canary while Redis continues serving 100% of reads",
      "Build Prometheus/Grafana dashboards tracking the four abort thresholds: p99 \u003e3ms, gossip \u003e100 Mbps, pub/sub \u003e5ms, \u003e2 node failures/7 days, plus cache hit ratio ≥85%",
      "Run canary for 2 weeks under shadow write load, comparing Valkey p99/p999 latency distributions against Redis baseline at equivalent traffic volume",
      "Benchmark Valkey pub/sub message throughput on the 20-node canary to validate the 100K messages/sec threshold before Phase 2 read shifting"
    ],
    "unknowns": [
      "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"
    ],
    "notice": "Concrete components, topology, and thresholds named below are candidate mitigations or example implementations inferred by the Council. They were not confirmed in your filing or established as part of your current environment."
  },
  "grounding_note": "Concrete components, topology, and thresholds named below are candidate mitigations or example implementations inferred by the Council. They were not confirmed in your filing or established as part of your current environment.",
  "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": "recommendation"
}