Database & Application Modernization Cut Licensing Costs and Improved System Performance for Tax Compliance MSP 

Facing high MSSQL overhead and technical debt from legacy architecture, Tax Compliance MSP successfully transitioned to a modern cloud-native stack centered around PostgreSQL and containerized services. The initiative ensured seamless migration of both data and logic, while preparing the platform for scalable, cost-effective growth.

The Tax Compliance MSP team recognized that while their MSSQL databases were stable, the licensing, performance limitations, and compatibility issues with modern DevOps pipelines were impeding future scalability. Refactoring efforts were delayed due to the perceived complexity of stored procedures, while platform costs continued to grow.

At the same time, their application architecture — initially designed for virtual machines — lacked containerized flexibility and had tight coupling between API layers and underlying databases. Scaling required manual efforts, and the infrastructure wasn’t optimized for elasticity or resilience.

To address this, the leadership team sought a modernization strategy that combined cost reduction, performance uplift, and operational flexibility, without interrupting the services relied on by hundreds of business users.

The legacy stack at Tax Compliance MSP was heavily reliant on Microsoft SQL Server, which introduced rising operational expenses due to high licensing fees, enterprise support contracts, and per-core pricing. The backend architecture was monolithic, making it difficult to isolate services or enable deployment independence — leading to longer release cycles and increased risk of regression. Additionally, backup and failover processes were manual, consuming valuable engineering time and creating inconsistencies in recovery procedures.

The business logic was embedded in complex T-SQL stored procedures, making any transition to open-source databases challenging. Attempts to migrate functionality using automated tools like AWS SCT often resulted in incomplete or non-optimized translations. These complexities introduced several risks, including the possibility of downtime during production migration, inconsistent function translation, and performance bottlenecks caused by heavy joins and long-running reports under MSSQL. With the cost of scaling and maintenance increasing, the leadership team recognized the urgency to modernize the database and application layers in a way that wouldn’t compromise service reliability.

Cygnet.One designed and delivered a staged modernization roadmap tailored to Tax Compliance MSP’s operational needs and risk profile. The engagement followed a hybrid approach; combining replatforming to PostgreSQL with selective refactoring — ensuring continuity of services while enhancing performance and cost efficiency.

The team began by converting the MSSQL schema using sqlserver2pgsql and AWS Schema Conversion Tool (SCT). While automated tools were used for initial translation, all critical stored procedures were manually rewritten in PL/pgSQL to ensure optimal execution and compliance with PostgreSQL best practices. This ensured data integrity and logic fidelity post-migration.

For non-production environments, the data was migrated using pgloader in a single-shot operation. For production, the team used AWS Database Migration Service (DMS) with Change Data Capture (CDC) enabled, allowing live data to sync from MSSQL to PostgreSQL without downtime. A dual-write validation window was maintained before cutover to ensure data parity and service continuity.

To support high concurrency and reduce latency, pgbouncer was implemented for connection pooling, while dblink and postgres_fdw extensions were used to replicate cross-database querying logic previously handled within MSSQL. On the application side, Cygnet engineers refactored core services for statelessness and deployed them using Amazon ECS with Fargate, enabling horizontal auto-scaling.

The final cutover was scheduled during an off-peak window. Rollback mechanisms using EBS snapshots and database dumps were pre-tested and documented. Post-switch, the team verified query performance, monitored replication health, and validated log ingestion volumes before decommissioning the legacy stack.

As a result, Tax Compliance MSP now operates on a PostgreSQL-backed architecture that is more cost-efficient, high-performing, and cloud-native. Fully prepared for rapid scaling, CI/CD-driven deployments, and future service expansions.