Zero-Downtime
Cloud Migration
How we migrated 14 on-premises services to Azure with zero downtime during peak trading hours — achieving 99.99% uptime and reducing infrastructure costs by 42%.
Client Context
A New York–based financial technology firm processed 2.3 million transactions daily through 14 interconnected services running on aging on-premises hardware. Their co-location contract was expiring in 6 months, the hardware was EOL, and the vendor quoted a 65% price increase for renewal.
The challenge: the platform could not tolerate even 30 seconds of downtime. Trading operations ran 22 hours a day (closed only during the 2-hour nightly settlement window). Any service interruption during market hours would trigger regulatory reporting obligations and potential fines exceeding $500K per incident.
They needed a complete migration to Azure — infrastructure, databases, message queues, and monitoring — without a single second of user-facing downtime.
Migration Without Interruption
Traditional "lift and shift" migration was impossible. The services were tightly coupled, the databases used features specific to SQL Server on-prem, and the deployment process was manual — SSH into servers and run scripts.
⏰ Zero Downtime Mandate
22 hours/day of active trading. The 2-hour settlement window wasn't long enough for a big-bang cutover. Migration had to be incremental, service-by-service, with instant rollback capability.
🔗 Tight Coupling
14 services communicated via direct TCP connections, shared database tables, and in-memory caches. Extracting one service required understanding and rerouting all its dependencies.
🔐 Regulatory Compliance
SOC 2 Type II, PCI DSS, and SEC audit requirements meant every infrastructure change needed documented approval, encrypted data in transit and at rest, and complete audit trails.
📊 No CI/CD Pipeline
Deployments were manual SSH sessions with handwritten runbooks. No infrastructure-as-code, no automated testing, no rollback mechanisms. A single typo in a config file had caused a 4-hour outage the previous quarter.
Strangler Fig Architecture
We implemented the Strangler Fig pattern — gradually routing traffic from on-prem services to Azure equivalents, one service at a time. An API gateway controlled traffic splitting, allowing 1%, 10%, 50%, then 100% cutover with instant rollback at every stage.
On-Premises (Before)
Azure (After)
01 — Terraform Everything
All Azure infrastructure defined in Terraform with remote state in Azure Blob Storage. Every change reviewed via PR, planned automatically, and applied through GitHub Actions. No manual infrastructure changes ever.
02 — AKS with GitOps
ArgoCD manages all Kubernetes deployments declaratively. Blue-green deployments with automated canary analysis. Failed health checks automatically roll back before traffic reaches the new version.
03 — Database Migration
Azure Database Migration Service for initial sync, then continuous replication. Cutover during settlement windows with automated data integrity checks — row counts, checksums, and sample query validation.
04 — Security Hardening
HashiCorp Vault for secrets management. Azure Private Endpoints eliminate public internet exposure. Network Security Groups and Azure WAF provide defense-in-depth. All communication mTLS encrypted.
Terraform + GitHub Actions Pipeline
Every infrastructure change follows the same path: PR → automated plan → peer review → merge → automated apply. The pipeline includes security scanning, cost estimation, and drift detection.
The AKS cluster spans 3 availability zones for hardware-level redundancy. Ephemeral OS disks improve node startup time from 8 minutes to 90 seconds. Calico network policies enforce zero-trust pod communication — services can only reach their declared dependencies.
Measurable Impact
The migration was completed over 14 weeks, with each service migrated during settlement windows. Total user-facing downtime: zero seconds.
| Metric | Before | After | Improvement |
|---|---|---|---|
| User-Facing Downtime | 12 hrs/quarter (avg) | 0 seconds | ▲ 99.99% uptime |
| Infrastructure Cost | $68K/month | $39K/month | ▲ 42% reduction |
| Deploy Frequency | Monthly (manual) | 12×/day (automated) | ▲ 360× faster |
| Mean Time to Recovery | 4.2 hours | 3.5 minutes | ▲ 98.6% faster |
| Security Posture | 3 open audit findings | SOC 2 Type II certified | ▲ Full compliance |
| Auto-Scaling | Manual VM provisioning | 0→100 in 90 seconds | ▲ Fully elastic |
Our board was terrified of this migration. We process billions in daily transactions and any downtime means regulatory scrutiny. Garnet Grid's strangler fig approach let us migrate one service at a time with instant rollback — we could pull the plug in 30 seconds if anything looked wrong. It never did. We went from dreading deployments to shipping 12 times a day with zero anxiety.
More Case Studies
Planning a Cloud Migration?
Let's architect a migration path that doesn't risk your uptime.
Start Your Project →