Introduction to Azure Cosmos DB Migration

Azure Cosmos DB is a globally distributed, multi-model database service that allows you to create and interact with NoSQL databases. This tutorial provides a step-by-step guide to help you migrate your existing data to Azure Cosmos DB, ensuring a smooth and efficient transition.

Why Migrate to Azure Cosmos DB?

  • Global Distribution: Distribute your data worldwide with multi-region writes and read replication.
  • Elastic Scalability: Scale throughput and storage elastically and independently across any number of regions.
  • Guaranteed SLAs: Achieve industry-leading, comprehensive SLAs covering availability, throughput, storage, and latency.
  • Multiple APIs: Support for various APIs including SQL (Core), MongoDB, Cassandra, Gremlin, and Table.
  • High Availability: Built-in high availability and disaster recovery capabilities.

Migration Strategies

There are several approaches to migrating your data to Azure Cosmos DB. The best strategy depends on your current data source, application dependencies, and downtime tolerance.

1. Lift and Shift (Offline Migration)

This method involves taking your existing database offline, migrating the data, and then bringing the new Cosmos DB instance online. It's suitable for applications that can tolerate downtime.

Steps:

  1. Export Data: Export your data from the source database into a portable format (e.g., JSON, CSV).
  2. Prepare Data: Cleanse and format the exported data to match the structure of your target Cosmos DB collection.
  3. Create Cosmos DB Account: Set up an Azure Cosmos DB account and create a database and container.
  4. Import Data: Use tools like the Azure Cosmos DB Data Migration Tool, Azure Data Factory, or custom scripts to import the data.
  5. Update Connection Strings: Reconfigure your application to connect to Azure Cosmos DB.
  6. Test and Deploy: Thoroughly test your application and deploy it.

2. Online Migration (Zero Downtime)

This strategy minimizes or eliminates application downtime by migrating data while the application remains online. It often involves continuous data synchronization.

Tools for Online Migration:

  • Azure Data Factory: A cloud-based ETL and data integration service that allows you to create data-driven workflows.
  • Azure Databricks: A unified, cloud-based platform for big data analytics and machine learning, which can be used for complex migration scenarios.
  • Cosmos DB Change Feed: Utilize the change feed to capture ongoing data changes in the source and replicate them to Cosmos DB.

Using the Azure Cosmos DB Data Migration Tool

The Azure Cosmos DB Data Migration Tool is a client-side GUI application that helps you migrate data from various sources (including SQL Server, MongoDB, CSV files, and Azure Table storage) into Azure Cosmos DB.

Installation and Usage

You can download the Data Migration Tool from the Azure portal. Once installed, you'll configure connection strings for both your source and target databases.

-- Example: Connecting to Azure Cosmos DB SQL API
<add key="CosmosDbConnectionString" value="AccountEndpoint=https://yourcosmosdb.documents.azure.com:443/;AccountKey=yourkeyhere="/>" />

Key Features:

  • Supports SQL API, Table API, Cassandra API, and MongoDB API.
  • Provides options for schema mapping and data transformation.
  • Allows for batch processing and monitoring of migration progress.

Best Practices for Migration

  • Plan Thoroughly: Understand your data, schema, and application dependencies before starting.
  • Choose the Right API: Select the Cosmos DB API that best matches your existing data model and application needs.
  • Optimize Throughput: Provision adequate Request Units (RUs) for your containers to handle the initial import and ongoing workload.
  • Monitor Performance: Continuously monitor your Cosmos DB performance during and after migration.
  • Test Rigorously: Conduct comprehensive testing to ensure data integrity and application functionality.
  • Consider Indexing: Understand Cosmos DB's indexing policies and optimize them for your query patterns.

Example: Migrating from SQL Server to Cosmos DB (SQL API)

This involves exporting SQL data, potentially transforming it to JSON, and then importing it using the Data Migration Tool or Azure Data Factory.

  1. Export SQL data to a CSV file.
  2. Use the Data Migration Tool to map CSV columns to Cosmos DB document properties.
  3. Configure your target Cosmos DB container.
  4. Run the import process.

Post-Migration Steps

  • Performance Tuning: Adjust RUs, indexing policies, and partition keys based on observed performance.
  • Application Validation: Confirm all application features work as expected with Cosmos DB.
  • Backup and Disaster Recovery: Configure and test backup and restore procedures for your Cosmos DB data.
  • Decommission Source: Once confident, decommission your old database system.