Cell-Based Architecture Style Evaluation

Wrote docs/architecture/styles/cell-based-style-evaluation.md. Complete Cell-Based Architecture style evaluation establishing 20 self-contained cellular units, deterministic merchant routing algorithms, zero cross-cell query invariants, and 5% blast-radius containment.

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skill: cell-based-style

Architecture Style Evaluation: Cell-Based Architecture [STYLE-CELL-001]

Summary

This specification establishes the architectural style evaluation of

Cell-Based Architecture (CBA) for payment-core-processing-platform v3.0 under run ID payment-cell-style-001. It evaluates architectural candidates for clearing payment authorizations across 24 million merchant accounts sustaining 45,000 peak requests/second. The evaluation resolves the catastrophic global blast-radius failures demonstrated in incident OUT-4811 (where a corrupted database migration script in a single shared Kubernetes cluster brought down 100% of global payment operations for 4.5 hours, incurring $12M in merchant SLA penalties). The evaluation compares three primary architecture styles: Monolithic Sharded Microservices, Global Multi-Region Active-Active, and

Cell-Based Architecture (20 Autonomous Cells). It selects Cell-Based Architecture as the optimal style, specifying 20 fully self-contained cellular replicas (each hosting dedicated compute, storage, and caching capped at 5% of global merchants), an ultra-lightweight cellular routing router, strict zero cross-cell transactional queries, and canary wave deployments.

Detailed Description

Operating massive cloud systems as a single shared platform creates catastrophic blast-radius risk. When thousands of microservices share common database clusters, service meshes, or control planes, a single software bug, poisoned message, or DNS misconfiguration can cascade across the entire estate. Cell-Based Architecture bounds blast radius by deploying multiple complete, fully independent, self-contained copies of the entire application stack ("cells"). A thin, highly reliable routing layer maps incoming requests to a specific cell based on a stable partition key. If Cell 04 experiences an unhandled kernel panic, database corruption, or outage, exactly 5% of merchants are impacted, while the remaining 95% continue operating normally.

Public Merchant Traffic Ingress (45,000 req/sec)
                         │
                         ▼
[ Tier 1 Edge: Cellular Routing Layer (Anycast + Envoy) ]
  ├── 1. Extracts Partition Key: `merchant_id` (e.g. `m_corp_8812`)
  └── 2. Consistent Hashing Router: Maps Key to Target Cell ID (Cell 04)
                         │
        ┌────────────────┼────────────────┐ (Zero Cross-Cell Traffic)
        ▼                ▼                ▼
[ Cell 01 (5% AUM) ]   [ Cell 04 (5% AUM) ]   [ Cell 20 (5% AUM) ]
  ├── Dedicated EKS      ├── Dedicated EKS      ├── Dedicated EKS
  ├── Dedicated Aurora   ├── Dedicated Aurora   ├── Dedicated Aurora
  └── Dedicated Redis    └── Dedicated Redis    └── Dedicated Redis

Criteria and weights

Comparison

Result

Option C is selected. 20 autonomous cells bound failure blast radius to exactly 5% of merchants; cellular routing layer directs traffic with sub-1ms overhead; deployment waves roll out 1 cell at a time.

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Required Mechanisms

1. Cellular Partitioning Model & Sizing [MC-CP-01]

• Cell Cardinality: Exactly 20 autonomous production cells.

Cell Capacity: Each cell sustains 2,250 requests/sec normal load with a burst capacity ceiling of

4,500 requests/sec.

• Tenant Distribution: 24 million merchant accounts are partitioned evenly (~ 1.2 million merchants per cell).

Failure Envelope: If an entire cell is obliterated (e.g. database corruption or bad deployment), global merchant availability remains at

95.0%.

2. Cellular Routing Layer & Sharding Key Strategy [MC-CR-01]

• Partition Key: Immutable merchant_id string.
• Routing Algorithm:
  $$\text{Cell ID} = \text{MurmurHash3}(\text{merchant_id}) \pmod{20}$$
• Routing Layer Implementation:
  • Stateless Envoy proxy running at cloud edge.
  • Zero database lookups required: computes target cell algorithmically in < 0.2 milliseconds.
  • Returns HTTP 503 strictly to the affected merchant cohort if target cell is unreachable.

3. State Independence & Zero Cross-Cell Queries [MC-SI-01]

Strict Invariant: A microservice in Cell $X$ is

physically prohibited from connecting to a database, cache, or message broker in Cell $Y$.

Network Enforcement: AWS VPC security groups and Kubernetes Calico/Cilium network policies block all inter-cell TCP traffic.

• Cross-merchant transactions (e.g. merchant $A$ in Cell 01 transferring funds to merchant $B$ in Cell 04) are processed via external asynchronous clearing rails (SWIFT/Fedwire) as separate two-legged events.

4. Cell Management Plane & Canary Wave Deployments [MC-CD-01]

• Canary Rollout Schedule:
  • Wave 0 (Canary): Deploy new release candidate to Cell 01 (5% traffic). Soak for 4 hours.
  • Wave 1: Deploy to Cells 02–05 (20% traffic). Soak for 2 hours.
  • Wave 2: Deploy to Cells 06–12 (35% traffic).
  • Wave 3: Deploy to remaining Cells 13–20 (40% traffic).
• Any Prometheus error rate anomaly in Wave 0 rolls back Cell 01 in < 30 seconds, shielding 95% of merchants from the defect.

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Invariants and Contracts

Five Percent Blast-Radius Ceiling [INV-CELL-01]
  No single infrastructure failure, database corruption, or software bug may impact more than
  one cell (5% of active merchant accounts) simultaneously.

Absolute Prohibition of Cross-Cell Queries [INV-CELL-02]
  Workloads within a cell must not initiate network connections or distributed database queries
  to data stores belonging to other cells. Cross-cell synchronous queries are blocked by network firewalls.

Deterministic Stateless Cellular Routing [INV-CELL-03]
  Cellular routing proxies must determine target cell routing deterministically via consistent hashing
  without performing dynamic relational database queries in the critical request path.

Explicit Unknowns

• Additional cloud infrastructure cost overhead of provisioning 20 baseline RDS Aurora clusters versus a shared database (G-1).
• Operational complexity of maintaining 20 concurrent schema migrations during bi-weekly releases (G-2).

Traceability

Verification

No validator was supplied, so no command was run.

Reviewer self-check against Cell-Based Architecture standards:

• Blast Radius Control: PASS. 20 cells cap any single outage to exactly 5% of global merchants.
• State Isolation: PASS. Independent databases per cell; zero cross-cell network paths.
• Routing Efficiency: PASS. Algorithmic MurmurHash3 routing adds < 0.2ms overhead.
• Markdown Hygiene: PASS. Native Markdown syntax strictly adheres to rule_markdown.md.

Open Decisions

• DEC-CELL-01: Elena Rostova to determine whether high-profile VIP Tier-1 merchants should be isolated into dedicated single-tenant "VIP Cells" (Owner: Elena Rostova).

Next steps

1. Marcus Vance provisions pilot Cellular Routing Envoy proxies with MurmurHash3 routing filters.
2. Platform team sets up Terraform modules to stamp out cellular VPC and EKS cluster templates.
3. Conduct staging resilience game day simulating total database destruction in Cell 01 to verify 95% of traffic continues unaffected.