5.1.3.2. Design for Database Migration Services

💡 First Principle: A purpose-built database migration service is essential for facilitating the secure, efficient, and often near-zero downtime transfer of databases to the cloud, addressing the unique challenges of data consistency, schema conversion, and continuous replication.

Scenario: You are tasked with migrating a large on-premises PostgreSQL database to Azure Database for PostgreSQL with minimal disruption to a 24/7 production application. You need a service that can keep the data synchronized during the migration and allow for a quick cutover.

Database migration services are Azure services designed to help you move your databases to Azure.

Key Design Considerations:

• Azure Database Migration Service (DMS):
  • Purpose: A fully managed service designed to enable seamless migrations from various database sources to Azure data platforms with minimal downtime.
  • Supported Sources: SQL Server, MySQL, PostgreSQL, Oracle, MongoDB.
  • Supported Targets: Azure SQL Database, Azure Database for MySQL/PostgreSQL/MariaDB, Azure Cosmos DB.
  • Migration Types: Supports offline (downtime required) and online (minimal downtime via continuous data synchronization) migrations.
• Migration Strategy:
  • Offline Migration: Suitable for applications that can tolerate downtime. Simpler and lower cost.
  • Online Migration: Ideal for mission-critical applications. DMS continuously synchronizes data, allowing for a seamless cutover.
• Assessment and Planning: Before migration, use tools like Data Migration Assistant (DMA) to assess database compatibility and identify potential migration blockers.
• Data Consistency and Integrity: Ensure data integrity throughout the migration process. DMS handles data synchronization and validation.

⚠️ Common Pitfall: Attempting a heterogeneous migration (e.g., Oracle to PostgreSQL) without using the associated Schema Conversion Tool. DMS migrates the data, but you often need a separate tool to convert the schema, stored procedures, and application code.

Key Trade-Offs:

• Online vs. Offline Migration: Online migration provides minimal downtime but is more complex and can be more costly due to the need for continuous replication infrastructure. Offline migration is simpler but requires a significant downtime window.

Reflection Question: How do database migration services (specifically Azure Database Migration Service (DMS) with its online migration capabilities) address the unique challenges of migrating databases (e.g., data consistency, downtime minimization) to ensure a secure and efficient transfer to Azure, particularly for mission-critical workloads?