Architecture

Legacy system → high-availability cloud

Distributed Azure architecture replacing a single-region on-premises deployment with multi-zone HA, automated failover, and zero-downtime migration.

azurekubernetessql-hyperscalehigh-availability

Architecture overview

This architecture replaces a monolithic on-premises application with a distributed Azure deployment designed for 99.9% availability across multiple failure domains.

Key components

Azure Kubernetes Service (AKS) — Application tier deployed across multiple availability zones. Horizontal pod autoscaling handles demand spikes. Rolling updates enable zero-downtime deployments.

Azure SQL Database Hyperscale — Database tier with active geo-replication. Automatic failover group with 2-minute RTO. Read replicas offload reporting workloads from the primary.

Azure Application Gateway — Layer 7 load balancer with WAF policy. Health probes route traffic away from unhealthy pods automatically.

Azure Front Door — Global traffic distribution and DDoS protection at the edge. Enables regional failover if an availability zone becomes unavailable.

Availability design

The system is designed to survive:

  • Single pod failure → AKS restarts pod, health probe routes traffic to healthy pods
  • Node failure → AKS reschedules pods to other nodes in the zone
  • Zone failure → AKS node pools span multiple zones; SQL geo-replication handles data
  • Region degradation → Front Door routes traffic to secondary region

Migration approach

This system was migrated live using a parallel-run pattern. The new Azure environment ran in shadow mode for three weeks before receiving production traffic.

The migration used five phases:

  1. Infrastructure provisioning and validation
  2. Application containerization
  3. Data replication via Azure Database Migration Service
  4. Gradual traffic shift (5% → 25% → 50% → 100%)
  5. Old infrastructure decommission after 30-day stability window