Business Background
The client is a global B2B SaaS provider operating a subscription-based revenue model across multiple regions and currencies. Its billing platform supports subscription management, usage-based billing, invoicing, payments, and revenue recognition for enterprise customers.
Over more than a decade of evolution, the platform grew in complexity and became a critical constraint on scalability, compliance, and release velocity.
Problem Statement
The client’s billing platform was implemented as a monolithic application built on the .NET Framework and hosted on on-premises infrastructure. As transaction volumes increased and regulatory requirements became more stringent, the platform began to introduce significant operational and business risk.
The existing architecture limited scalability, slowed delivery, and made it increasingly difficult to meet reliability and compliance expectations for a revenue-critical system.
Key Challenges
- Billing batch jobs degraded online user performance
- Scaling required full application scale-out, increasing cost and operational risk
- Quarterly release cycles limited responsiveness to pricing and regulatory changes
- Disaster recovery processes were manual, with no regular failover testing
- Audit trails were incomplete, creating gaps in SOX and PCI compliance
- Reporting workloads negatively impacted billing execution
- Month-end and quarter-end billing runs carried high operational risk
Solution Overview
The client modernized its billing and revenue platform in a step-by-step manner using Microsoft Azure and .NET 8. Instead of changing everything at once, the platform was gradually upgraded to reduce risk and avoid disruption to ongoing billing operations.
The goal was to move away from a single, tightly connected system and build a domain-aligned, event-driven architecture that could handle growth, improve reliability, and meet compliance needs.
Solution Highlights
- The platform was broken into smaller services (microservices), each aligned to a specific billing function
- Event-driven processing was used so billing, invoicing, and revenue recognition could run independently
- Built-in Azure monitoring, security, and compliance controls were applied across the system
- A central data platform was created using Azure Data Lake Gen2 to store billing history, audit data, and analytics
Architecture Solution
The platform was designed to separate billing, analytics, and integration workloads, improving scalability, reliability, and security.
Key components
Compute
- Azure Kubernetes Service (AKS) runs the core billing services
- Azure Functions handle billing triggers and events
Data
- Azure SQL Database for transactional billing data
- Azure Data Lake Gen2 for billing history, audit logs, and analytics
- Azure Synapse Analytics for finance and revenue reporting
Integration
- Azure Service Bus enables asynchronous workflows
- Azure API Management manages internal and external APIs
Security & Governance
- Azure Entra ID with managed identities for access control
- Azure Key Vault for secrets management
- Private endpoints and network isolation to protect sensitive data
Implementation Approach
Phase 1: Discovery and Stabilization
- Analyzed existing billing logic and data relationships to fully understand platform behavior
- Introduced CI/CD pipelines to standardize builds and deployments
- Moved the legacy monolithic system to Azure IaaS to reduce immediate infrastructure risk
Phase 2: Incremental Decomposition
- Defined clear functional boundaries across subscriptions, pricing, billing, and invoicing
- Enabled event-driven workflows using Azure Service Bus to decouple processing
- Gradually separated services using the Strangler Fig approach while keeping the legacy system operational
Phase 3: Cloud Optimization
- Shifted modernized services to Azure Kubernetes Service (AKS) and managed Azure PaaS platforms
- Enabled autoscaling and dedicated compute to isolate billing workloads
- Established centralized monitoring and audit logging for operational visibility
Phase 4: Analytics and Compliance Enablement
- Created a finance-grade data lake to store long-term billing and revenue data
- Enabled revenue analytics through Azure Synapse Analytics and Power BI
- Implemented immutable audit storage with defined data retention and lifecycle policies
Outcomes and Business Impact
Operational Outcomes
- Billing workloads were fully isolated from customer-facing systems, removing performance impact during billing cycles
- Deployment processes supported zero-downtime releases through controlled blue and green deployment patterns
- Failover and disaster recovery were automated and regularly tested to improve platform resilience
- Incident detection and resolution improved through distributed tracing and centralized observability
Business Outcomes
- New pricing structures and subscription models could be introduced faster with lower operational risk
- Improved billing accuracy reduced customer disputes and rework for finance teams
- Stronger audit readiness increased confidence in regulatory and compliance processes
- Overall infrastructure and operational costs were reduced through better resource utilization
Key Performance Indicators (KPIs)
Delivery & Agility
| KPI | Before | After |
| Release frequency | Quarterly | Weekly |
| Lead time for changes | 8–10 weeks | < 2 weeks |
| Deployment failures | High | < 2% |
Scalability & Performance
| KPI | Before | After |
| Billing throughput | Baseline | 10× capacity |
| Peak billing duration | 12–14 hours | < 3 hours |
| Online user impact during billing | Frequent | None |
Reliability & Resilience
| KPI | Before | After |
| Platform availability | ~99.5% | 99.95% |
| RPO | Manual | ≤ 5 minutes |
| RTO | Several hours | ≤ 30 minutes |
Compliance & Governance
| KPI | Before | After |
| Audit evidence retrieval | Days | Minutes |
| SOX control gaps | Multiple | Eliminated |
| Billing audit coverage | Partial | 100% |
Cost Optimization
| KPI | Impact |
| Infrastructure cost | ~25–30% reduction |
| Storage cost for history | Reduced via tiering |
| Compute efficiency | Autoscaling aligned to billing cycles |
Conclusion
The modernization effort transformed the billing platform from a high-risk monolithic system into a scalable, resilient, and compliant cloud-native revenue platform.
By following an incremental modernization approach and using Azure-native services, the client improved delivery agility, platform reliability, and financial governance while ensuring that day-to-day business operations continued without disruption.