Managing Geo-Replication for Azure SQL Database

This tutorial guides you through the process of setting up and managing geo-replication for your Azure SQL databases. Geo-replication is a powerful feature that allows you to maintain readable copies of your databases in different geographical regions, providing high availability and disaster recovery capabilities.

Note: Geo-replication is built on the concept of active geo-secondary databases. These are readable secondary databases that are automatically kept up-to-date with your primary database.

Prerequisites

An active Azure subscription.
An Azure SQL Database or an Azure SQL Managed Instance.
Appropriate permissions to manage Azure resources.

Understanding Geo-Replication Concepts

Geo-replication leverages the Azure SQL Database's built-in replication capabilities to create and manage read-only secondary replicas in different Azure regions. The primary database transactions are asynchronously replicated to the geo-secondary database.

Key Components:

Primary Database: The original, read-write database.
Active Geo-Secondary Database: A read-only replica in a different Azure region. It's automatically kept up-to-date with the primary.
Failover Groups: A higher-level abstraction that allows you to manage failover of multiple databases across regions and provides a listener endpoint for seamless application connectivity.

Steps to Configure Geo-Replication

1. Create a Geo-Secondary Database

You can create a geo-secondary using the Azure portal, PowerShell, or Azure CLI.

Using Azure Portal:

Navigate to your Azure SQL Database in the Azure portal.
In the database's overview page, find the "Geo-replication" section.
Click on "Create secondary".
Configure the secondary database's region, performance tier, and other settings.
Click "Create".

Using Azure CLI:

Use the following command to create a geo-secondary:

az sql db replica create --resource-group myresourcegroup --server myserver --name mydatabase --partner-resource-group mypartnerresourcegroup --partner-server mypartner

2. Monitor Replication Status

You can monitor the replication lag and status through the Azure portal or by querying system views.

Querying Replication Status:

Use the following query to check the replication status of a geo-secondary:

SELECT
                replication_state_desc,
                replication_lag_sec,
                last_replication_update_date
            FROM
                sys.dm_geo_replication_link_status
            WHERE
                partner_server = 'your_primary_server_name.database.windows.net';

3. Managing Failover

In case of a disaster or planned maintenance, you can initiate a failover to the geo-secondary database.

Manual Failover (Recommended: Failover Groups):

While direct manual failover of a single database is possible, using Failover Groups provides a more robust and manageable solution for failover.

Using Azure Portal with Failover Groups:

Navigate to your Azure SQL Server.
Under "Data management", select "Failover groups".
Configure a new failover group, linking your primary and secondary databases.
To failover, select the failover group and click "Failover now".

Tip: For minimal application downtime, plan your failover during off-peak hours. Ensure your application is configured to connect to the listener endpoint provided by the failover group.

Key Considerations

Latency: Geo-replication is asynchronous. There will always be a replication lag, which can vary based on network conditions and database load.
Cost: Geo-secondary databases incur costs similar to active databases, including storage and compute.
Failover Time Objective (FTO): While Azure aims for rapid failover, the actual time depends on several factors, including the number of databases in the failover group and the replication lag.
Application Connectivity: Using Failover Groups simplifies application connectivity by providing a consistent listener endpoint that automatically redirects to the active primary.

Advanced Geo-Replication Scenarios

Multiple Geo-Secondaries: You can create multiple geo-secondaries in different regions for enhanced redundancy.
Read-Scale Workloads: Active geo-secondaries can be used for read-intensive workloads in their respective regions to improve query performance and reduce latency for users in those locations.

Warning: Direct failover of a single database should be used with caution. Failover Groups are the recommended approach for production environments as they manage application connectivity and coordinated failover of multiple databases.

Conclusion

Geo-replication is an essential feature for ensuring the availability and durability of your Azure SQL databases. By understanding its concepts and following the steps outlined in this tutorial, you can effectively implement and manage geo-replication for your critical data.