Pattern 86 / MIGRATE

Parallel Run

Use this when Validating a new system against an old one.

Pressure: Validating a new system against an old one
Mechanism: Run both paths, compare outputs, and keep one authoritative until confidence is high
Toll: Double-running increases cost and comparison logic must handle legitimate differences

Diagram for Parallel Run — Architecture plate86

Executive brief

Parallel Run fits when Validating a new system against an old one. Mechanism: Run both paths, compare outputs, and keep one authoritative until confidence is high. Use it for Billing, risk scoring, recommendation rewrites. The toll: Double-running increases cost and comparison logic must handle legitimate differences.

Use when

Billing, risk scoring, recommendation rewrites.

Example

Use parallel run when billing, risk scoring, recommendation rewrites..

Review framing

Describe the pressure first, then the mechanism, then the cost. That keeps the design grounded.

Same pressure family

Migration

84Strangler Fig 85Branch by Abstraction