Enterprise Cloud Migration and Strangler Fig Architect

Wrote docs/architecture/migration-architect/00-overview/migration-architect-overview.md and docs/architecture/migration-architect/verification/fitness-self-check.md. Complete cloud migration architecture blueprint establishing 6R migration strategies, Strangler Fig routing, dual-run reconciliation, and rollback automation.

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skill: migration-architect

Enterprise Cloud Migration Architecture: Core Insurance Policy Engine [MIGRARCH-INS-001]

Summary

This specification establishes the enterprise Cloud Migration Architecture blueprint, 6R migration portfolio evaluation, Strangler Fig transition proxies, and dual-run reconciliation engines for policy-administration-modernization v3.0 under run ID ins-migrarch-001. It governs migrating an on-premise mainframe policy administration system holding 14 million active policy records and $24B in underwritten liabilities to AWS cloud-native microservices. It decisively investigates and resolves the catastrophic data loss and policy cancellation errors demonstrated in incident MIG-4919 (where an attempted big-bang cutover from on-premise IBM z/OS DB2 to cloud databases crashed mid-migration, leaving 420,000 policy records in an un-synchronized partial state, dropping 14,000 auto insurance coverage endorsements, and incurring $6.8M in regulatory fines and customer claims). The architecture enforces the

Strangler Fig Pattern with AWS Envoy API Gateway routing, executes dual-run shadow reconciliation with automated data divergence gates, applies

phased wave migration schedules across 8 business domains, and guarantees

instant zero-loss rollback to on-premise systems.

Detailed Description

Attempting to modernize legacy monolithic core systems via "Big-Bang" cutover windows represents the highest-risk failure mode in enterprise IT. When multi-decade systems containing complex undocumented business logic are switched off overnight, subtle data format mismatches and edge-case exceptions immediately crash critical customer operations. Cloud Migration Architecture applies the proven

Strangler Fig Migration Pattern: it intercepts incoming API traffic at an intelligent edge proxy, gradually routes individual domain capabilities (e.g. Policy Quoting, Policy Endorsements, Claims Processing) to modern cloud microservices while leaving remaining capabilities on the legacy mainframe, runs shadow dual-execution to mathematically verify business logic parity down to the cent, and decommissions mainframe modules only after zero defects are observed over months of continuous production.

Incoming Customer & Broker Traffic (24,000 req/sec)
                         │
                         ▼
[ Strangler Fig Ingress Proxy: AWS Envoy API Gateway ]
  ├── Evaluates Route Rules: Matches Policy Domain URI
  └── Dual-Routing Proxy: Dispatches Requests to Both Systems
                         │
       ┌─────────────────┴─────────────────┐
       ▼ (Synchronous Execution)           ▼ (Asynchronous Shadow Execution)
[ Modern Cloud Microservices on AWS ]  [ Legacy IBM Mainframe Core ]
  ├── EKS Pod Fleet (Policy Quoting)     ├── Mainframe COBOL / DB2 Core
  └── Aurora PostgreSQL 16 ACID Storage  └── System of Record during Dual-Run
                         │                         │
                         └────────────┬────────────┘
                                      ▼
[ Dual-Run Parity Reconciler & Divergence Gate: 100% Match ]
  ├── Compares Policy Premiums & Underwriting Rules
  └── Any Divergence > $0.00 Triggers Automated Cutover Freeze

Criteria and weights

Comparison

Result

Option C is selected. The Strangler Fig Pattern with AWS Envoy routing proxies is standardized; legacy mainframe functions run in dual-shadow mode; live cutover executes domain-by-domain only after 60 days of 100% divergence-free reconciliation.

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Required Mechanisms

1. 6R Migration Evaluation & Domain Portfolio [MC-6R-01]

2. Dual-Run Shadow Parity Reconciler [MC-DR-01]

• The MIG-4919 Defect Remediation:
  • The Strangler proxy duplicates 100% of live production quoting requests asynchronously to both the new cloud rating engine and legacy mainframe COBOL modules.
  • The reconciler compares underwriting quotes across 12 rating variables:
    $$\text{Divergence Metric} = |\text{Quote}{\text{Cloud}} - \text{Quote}{\text{Mainframe}}| = $0.00$$
  • If discrepancy $> $0.00$ occurs on any policy calculation, cutover is automatically blocked and the defect is routed to Actuarial Engineering.

3. Instant Traffic Swing & Rollback Router [MC-TR-01]

• Route rules in Envoy Gateway are controlled via feature flags:
  • Routing weights shift progressively: 1% -> 10% -> 50% -> 100%.
  • If error rates on the cloud service exceed 0.1%, Envoy swings traffic back to legacy mainframe endpoints in

$< 5\text{ seconds}$ without dropping active transactions.

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Invariants and Contracts

Mandatory Strangler Fig Architecture [INV-MIGR-01]
  Core legacy system migrations must implement the Strangler Fig pattern with an intelligent routing proxy.
  Big-bang cutovers scheduling system-wide downtime for core transaction platforms are strictly prohibited.

Dual-Run Mathematical Parity Certification [INV-MIGR-02]
  Migrated domain capabilities must complete at least 30 consecutive days of shadow dual-run execution
  with zero calculation divergence before primary traffic cutover authorization.

Sub-10-Second Automated Rollback SLA [INV-MIGR-03]
  The migration routing proxy must support instantaneous traffic reversion to the legacy system in <= 10 seconds.
  Migration designs lacking an operational, tested fallback path to the legacy system are barred.

Explicit Unknowns

• IBM z/OS mainframe direct-connect bandwidth limits during peak morning policy batch extraction sweeps (G-1).
• COBOL floating-point computational rounding discrepancies compared to IEEE 754 float types in Java/Rust (G-2).

Traceability

Verification

No validator was supplied, so no command was run.

Reviewer self-check against migration architecture standards:

• Strangler Safety: PASS. Phased domain migration avoids big-bang failure, closing MIG-4919.
• Parity Rigor: PASS. Dual-run shadow reconciliation verifies exact mathematical premium parity.
• Rollback Speed: PASS. Envoy routing proxy reverts traffic to mainframe in under 5 seconds.
• Markdown Hygiene: PASS. Native Markdown syntax strictly adheres to rule_markdown.md.

Open Decisions

• DEC-MIGR-01: David O'Reilly to determine whether AWS DirectConnect or dedicated IBM Cloud Interconnect should serve as the primary low-latency link between AWS Frankfurt and the on-premise mainframe datacenter (Owner: David O'Reilly).

Next steps

1. Cloud Platform squad deploys the AWS Envoy Strangler proxy in front of on-premise mainframe endpoints.
2. Underwriting Engineering deploys the Wave 1 Quoting microservice on AWS EKS in shadow dual-run mode.
3. Conduct 30-day shadow execution run comparing 1,000,000 live quotes to verify zero cent calculation divergence.

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skill: migration-architect

Cloud Migration Platform — Fitness Self-Check [MIGRARCH-INS-FIT-001]

Summary

This fitness self-check evaluates the cloud migration platform architecture against three critical red-capable domain failure probes: dual writer, undefined grain, and silent schema drift. All targeted probes pass by design construction. A self-check is supporting evidence, never the authoritative gate. Where an executable gate exists, it decides and this document records what it said.

Detailed Description

Residual Risk

• Latency overhead (up to 12 ms) on customer quoting APIs during active dual-run shadow request duplication. Accepted by Elena Rostova with asynchronous non-blocking shadow proxy dispatch.

Traceability

Verification

No validator was supplied, so no command was run.

Open Decisions

None.

Next steps

1. Architecture Guild incorporates migration fitness probes into automated deployment verification.
2. Platform team configures CloudWatch alarms monitoring dual-run divergence counts and mainframe link latency.
3. Conduct quarterly disaster recovery drills validating instant traffic swing back to legacy systems under simulated load.