Core banking migration to a hybrid cloud

The primary data centre of a mid-sized joint-stock bank was approaching the end of its lease, and most of its servers were already out of warranty. Rather than fund another hardware refresh, the bank chose a hybrid cloud model: sensitive data stays in a certified private facility, while everything else runs on a public cloud region located in Vietnam. Zentrova owned the programme end to end, from the initial assessment to post-migration operations.

The challenge

The bank ran 46 systems holding roughly 180 TB of data, with many undocumented dependencies between applications. Provisioning a single test environment took three weeks on average, slowing every new initiative. Regulation required disaster recovery within four hours, yet the existing recovery plan had never been rehearsed in full. Any plan also had to keep branches, ATMs and digital channels running throughout, and leadership wanted infrastructure spending to move from large up-front purchases to a predictable, usage-based model.

Our solution

• Application assessment sorting every workload into one of six paths: retain, rehost, replatform, re-architect, replace or retire.
• Standardised landing zone built with Terraform, with network segmentation by data sensitivity and centralised key management.
• Continuous data replication between old and new environments, allowing a full rollback within 30 minutes if anything went wrong.
• 28 applications containerised and run on Kubernetes with load-based autoscaling.
• Five migration waves, each executed over a weekend and rehearsed twice beforehand.
• Compliance controls mapped to ISO 27001 and PCI DSS, with centralised access logs ready for audit at any time.

Results

Within 14 months all 46 systems were running on the new platform, and the bank's 1.8 million customers did not lose a single business day of service.

• Annual infrastructure cost reduced by 32%.
• Test environment provisioning cut from three weeks to 45 minutes.
• Core system availability of 99.98% in the first 12 months.
• Disaster recovery measured in rehearsal at 1 hour 50 minutes.
• End-of-day batch processing reduced from five hours to 2 hours 10 minutes.

Beyond the numbers, the migration changed how the technology team works. Infrastructure is now defined as code and reviewed like any other change, new environments are requested through a self-service portal, and the bank's own engineers run the platform day to day, with Zentrova acting as a second-line support partner.

For the first time, we ran a full disaster recovery drill without holding our breath for the outcome. — Chief Technology Officer, client bank