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ADR-009: Multi-Region Architecture

Status: Accepted

Date: 2026-01-25

Context

Need to support service deployment across multiple AWS regions to reduce latency and ensure disaster recovery.

Options Considered

  1. Single-region with manual failover
  2. Active-Active multi-region with cross-region communication
  3. Active-Active multi-region with isolated regions

Decision

Adopt Active-Active multi-region with isolated regions. Each region is self-contained, with no direct communication between services from different regions.

Rationale

  • Isolation: True disaster recovery - failure in one region does not affect others
  • Simplicity: Does not require mesh federation, cross-region service discovery, or conflict resolution
  • Latency: Users are routed to the nearest region via Route53 latency-based routing
  • Consistency: Each region has its own data, avoiding eventual consistency issues

Consequences

  • Directory structure: environments/{env}/{region}/
  • ECR centralized in us-east-1 (cross-region pull)
  • Central Grafana in prod/us-east-1 with remote datasources
  • Phased rollout: deploy region by region with configurable delays
  • Cost: resource multiplication per region

Structure

┌─────────────────────────────────────────────────────────────────┐
│                       Isolated Regions                           │
│                                                                  │
│  us-east-1 (Primary)              sa-east-1 (Secondary)         │
│  ┌─────────────────────┐         ┌─────────────────────┐        │
│  │ VPC + EKS + Keycloak│         │ VPC + EKS + Keycloak│        │
│  │ + Observability     │   ✕     │ + Observability     │        │
│  └─────────────────────┘         └─────────────────────┘        │
│         ▲                               ▲                        │
│         │     Route53 (DNS)             │                        │
│         └───────────────────────────────┘                        │
└─────────────────────────────────────────────────────────────────┘