Evaluate HA/DR for hybrid deployments

When implementing a hybrid deployment of Microsoft Azure SQL solutions, it is crucial to evaluate high availability (HA) and disaster recovery (DR) options. HA/DR ensures the availability and resiliency of your SQL databases, protecting against potential downtime and data loss. In this article, we will explore the various HA/DR strategies you can employ for hybrid deployments in accordance with the guidelines provided by Microsoft.

Understanding Hybrid Deployments

A hybrid deployment involves combining on-premises and cloud-based resources. It allows you to leverage the benefits of cloud computing while maintaining certain workloads locally. In the context of Azure SQL solutions, this typically means having on-premises SQL Server instances alongside Azure SQL Databases or Managed Instances.

High Availability for On-Premises SQL Server

For on-premises SQL Server instances, HA can be achieved using features like failover clustering and database mirroring. Failover clustering enables multiple SQL Server instances to work together, providing failover support in case one becomes unavailable. Database mirroring, on the other hand, allows databases to have hot standby copies on separate servers, ensuring data availability.

Hybrid HA/DR Options for Azure SQL Solutions

Azure offers several HA/DR options for hybrid deployments:

• Geo-Replication: Azure SQL Database and Managed Instance support geo-replication, allowing you to create readable secondary replicas in different Azure regions. These replicas can be used for disaster recovery, and they also enable read-only access to offload reporting or analytics workloads.
• Always On Availability Groups: By leveraging Windows Server Failover Cluster (WSFC) on-premises and combining it with Azure Virtual Machines (VMs), you can create an Always On Availability Group (AG). AGs provide both HA and DR capabilities, ensuring automatic failover and availability across regions.
• Active Geo-Replication: In addition to geo-replication, Azure SQL Database offers Active Geo-Replication, which allows you to create up to four readable secondary databases in different regions. This feature provides low recovery point objective (RPO) and recovery time objective (RTO) for DR scenarios.
• Log Shipping: For hybrid deployments with SQL Server instances, you can implement log shipping. Log shipping involves regularly backing up and copying transaction logs from the primary on-premises database to a secondary database in Azure. In case of a failure, the secondary database can be brought online quickly.
• Azure Site Recovery: Azure Site Recovery (ASR) is a comprehensive DR solution that replicates virtual machines, physical servers, and Azure VMs to a secondary Azure region. By using ASR, you can protect your entire hybrid deployment, including SQL Server instances, from site-wide outages or disasters.

Considerations for Hybrid HA/DR

When evaluating HA/DR strategies for hybrid deployments, consider the following aspects:

• RPO and RTO: Define your recovery point objective (RPO) and recovery time objective (RTO) to determine the appropriate HA/DR solution. RPO specifies the maximum acceptable data loss, while RTO defines the target time for recovery.
• Bandwidth and Latency: Assess the available network bandwidth and latency between your on-premises environment and Azure. This evaluation is crucial, especially when choosing options like active geo-replication or log shipping, as they rely on data synchronization.
• Costs: Consider the costs associated with the different HA/DR options. Some solutions may have additional licensing requirements or incur higher data transfer costs, which should be factored into your decision-making process.

Implementation and Testing

After selecting the appropriate HA/DR strategy for your hybrid deployment, thoroughly test the failover and recovery processes. Regularly perform drills and exercises to ensure that your HA/DR mechanisms are functioning as expected and meeting the defined RPO and RTO objectives.

In conclusion, evaluating HA/DR options is essential when deploying hybrid Azure SQL solutions. By understanding the available options and considering factors like RPO, RTO, bandwidth, latency, and costs, you can implement a robust and resilient architecture. Remember to regularly test your HA/DR mechanisms to maintain confidence in the recoverability of your hybrid deployment.