Moving a cross-border payments app to AWS with zero downtime

// the challenge

A cross-border payments company had outgrown its DigitalOcean setup and needed the availability and reach of AWS — but it moves real money, so it couldn't take an outage, and it couldn't drop the IPsec tunnels connecting it to banking and telecom partners. A big-bang switchover would have risked both live transactions and every partner integration at once.

// our approach

• Planned a phased cutover so traffic could shift gradually and be rolled back at any step, instead of one irreversible switch.
• Rebuilt the data tier on Multi-AZ RDS, ElastiCache, and EFS so the new environment was highly available from day one.
• Used AWS DMS with change data capture to keep the old and new databases continuously in sync right up to the final cutover.
• Tweaked network configurations to ensure the existing tunnels with partners kept working throughout the migration.

// the outcome

The application now runs on highly available, Multi-AZ AWS infrastructure with no disruption to payments during the migration. Because the databases were kept in sync with CDC, the cutover happened with no data loss and effectively zero downtime — and every partner tunnel stayed live throughout.