# ADR-001: Architecture Decisions

## Status
Accepted

## Context
ISO-20022 Combo Flow system requires decisions on architecture patterns, technology choices, and design principles.

## Decisions

### 1. Two-Phase Commit (2PC) Pattern
**Decision**: Use 2PC for atomic execution across DLT and banking rails.

**Rationale**:
- Ensures atomicity across heterogeneous systems
- Provides rollback capability
- Industry standard for distributed transactions

### 2. PostgreSQL for Persistence
**Decision**: Use PostgreSQL as primary database.

**Rationale**:
- ACID compliance required for financial transactions
- JSONB support for flexible plan storage
- Strong ecosystem and tooling

### 3. Redis for Caching
**Decision**: Use Redis for caching and session management.

**Rationale**:
- High performance
- Pub/sub support for real-time updates
- Widely supported

### 4. Smart Contract Architecture
**Decision**: Separate handler, registry, and adapter contracts.

**Rationale**:
- Modularity and upgradeability
- Security isolation
- Easier testing and auditing

### 5. Next.js for Frontend
**Decision**: Use Next.js 14 with App Router.

**Rationale**:
- Server-side rendering for performance
- Built-in API routes
- Excellent developer experience

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**Date**: 2025-01-15  
**Author**: Engineering Team