Fintech Core to AWS: Zero-Downtime Migration

Replatforming 80 core banking and ledger services to AWS with shadow dual-write cutover, multi-AZ Aurora PostgreSQL, and automated rollback guardrails.

Client Industry Fintech / Payments

Duration 8 Weeks Cutover

Role Lead Cloud Architect

Primary Stack AWS · EKS · Aurora · IaC

0 sec

Downtime during cutover

Deploy frequency increase

34%

Monthly AWS spend cut

99.995%

Production API availability

Financial trading charts on a monitor for the fintech platform migration

Architectural Flow Blueprint

Route 53 DNS Weighted Canary Routing

→

Dual-Write Proxy Replication & Sync Gateway

→

EKS Microservices Karpenter Autoscaling Pods

→

Aurora Multi-AZ Global Read Replicas

The Challenge

The client processed over $40M daily across a legacy colocation data centre. Deployments were monthly 6-hour night shifts prone to rollbacks. Any transaction drop would breach strict banking SLAs and risk financial penalties.

Zero Downtime Constraint

Payment settlement endpoints had to stay live without dropping inflight transactions or generating duplicate debits during the cutover window.

PCI-DSS Compliance

All data in transit and at rest required dedicated KMS customer-managed encryption keys with strict IAM least-privilege boundaries.

The Architecture Strategy

Rather than a risky "big bang" migration, we implemented a phased shadow dual-write pattern:

Phase 1 · Foundations

Terraform Landing Zone & VPC Peering

Set up AWS Organizations with dedicated Accounts for staging, compliance, and production. Deployed encrypted multi-AZ transit gateways and Direct Connect.

Phase 2 · Dual-Write & Shadow Testing

Asynchronous Data Replication

Built an event-driven replication layer using AWS DMS and Kafka to mirror all live transactions to Amazon Aurora with sub-10ms divergence monitoring.

Phase 3 · Live Cutover

Canary Traffic Shift via Route 53

Shifted user traffic 5% → 25% → 100% over 48 hours with continuous automated anomaly detection and immediate fallback paths.

Technologies Employed

AWS EKS Amazon Aurora PostgreSQL Terraform AWS Direct Connect ArgoCD (GitOps) Prometheus & Datadog AWS KMS Karpenter

Key Deliverables Handed to Client

14 audited, reusable Terraform modules

Automated canary deployment pipelines

Disaster recovery drill runbooks (RTO < 15 min)

8 hands-on training sessions with client engineers