Business continuity and disaster recovery (BCDR): Azure Paired Regions
What are paired regions?
An Azure region consists of a set of data centers deployed within a latency-defined perimeter and connected through a dedicated low-latency network. This ensures that Azure services within an Azure region offer the best possible performance and security.
An Azure geography defines an area of the world containing at least one Azure region. Geographies define a discrete market, typically containing two or more regions, that preserve data residency and compliance boundaries. Find more information about Azure's global infrastructure here
A regional pair consists of two regions within the same geography. Azure serializes platform updates (planned maintenance) across regional pairs, ensuring that only one region in each pair updates at a time. If an outage affects multiple regions, at least one region in each pair will be prioritized for recovery.
Some Azure services take further advantage of paired regions to ensure business continuity and to protect against data loss. Azure provides several storage solutions that take advantage of paired regions to ensure data availability. For example, Azure Geo-redundant Storage (GRS) replicates data to a secondary region automatically, ensuring that data is durable even in the event that the primary region isn't recoverable.
Note that not all Azure services automatically replicate data, nor do all Azure services automatically fall-back from a failed region to its pair. In such cases, recovery and replication must be configured by the customer.
Can I select my regional pairs?
No. Some Azure services rely upon regional pairs, such as Azure's redundant storage. These services don't allow you to create new regional pairings. Similarly, because Azure controls planned maintenance and recovery prioritization for regional pairs, you can't define your own regional pairs to take advantage of these services. However, you can create your own disaster recovery solution by building services in any number of regions and leveraging Azure services to pair them.
For example, you can use Azure services such as AzCopy to schedule data backups to a Storage account in a different region. Using Azure DNS and Azure Traffic Manager, customers can design a resilient architecture for their applications that will survive the loss of the primary region.
Am I limited to using services within my regional pairs?
No. While a given Azure service may rely upon a regional pair, you can host your other services in any region that satisfies your business needs. An Azure GRS storage solution may pair data in China East with a peer in China North while using Compute resources located in China East 2.
Must I use Azure regional pairs?
No. Customers can leverage Azure services to architect a resilient service without relying on Azure's regional pairs. However, we recommend that you configure business continuity disaster recovery (BCDR) across regional pairs to benefit from isolation and improve availability. For applications that support multiple active regions, we recommend using both regions in a region pair where possible. This ensures optimal availability for applications and minimized recovery time in the event of a disaster.
Azure Regional Pairs
| Geography | Regional Pair A | Regional Pair B |
|---|---|---|
| China | China North | China East |
| China | China North 2 | China East 2 |
An example of paired regions
The image below illustrates a hypothetical application that uses the regional pair for disaster recovery. The green numbers highlight the cross-region activities of three Azure services (Azure compute, storage, and database) and how they're configured to replicate across regions. The unique benefits of deploying across paired regions are highlighted by the orange numbers.
Figure 2 – Hypothetical Azure regional pair
Cross-region activities
As referred to in figure 2.
Azure Compute (IaaS) – You must provision additional compute resources in advance to ensure resources are available in another region during a disaster. For more information, see Azure resiliency technical guidance.
Azure Storage - If you're using managed disks, learn about replicating VMs from one region to another with Azure Site Recovery. If you're using storage accounts, then geo-redundant storage (GRS) is configured by default when an Azure Storage account is created. With GRS, your data is automatically replicated three times within the primary region, and three times in the paired region. For more information, see Azure Storage Redundancy Options.
Azure SQL Database – With Azure SQL Database Geo-Replication, you can configure asynchronous replication of transactions to any region in the world; however, we recommend you deploy these resources in a paired region for most disaster recovery scenarios. For more information, see Geo-Replication in Azure SQL Database.
Azure Resource Manager - Resource Manager inherently provides logical isolation of components across regions. This means logical failures in one region are less likely to impact another.
Benefits of paired regions
Physical isolation – When possible, Azure prefers at least 300 miles of separation between datacenters in a regional pair, although this isn't practical or possible in all geographies. Physical datacenter separation reduces the likelihood of natural disasters, civil unrest, power outages, or physical network outages affecting both regions at once. Isolation is subject to the constraints within the geography (geography size, power/network infrastructure availability, regulations, etc.).
Platform-provided replication - Some services such as Geo-Redundant Storage provide automatic replication to the paired region.
Region recovery order – In the event of a broad outage, recovery of one region is prioritized out of every pair. Applications that are deployed across paired regions are guaranteed to have one of the regions recovered with priority. If an application is deployed across regions that are not paired, recovery might be delayed – in the worst case the chosen regions may be the last two to be recovered.
Sequential updates – Planned Azure system updates are rolled out to paired regions sequentially (not at the same time) to minimize downtime, the effect of bugs, and logical failures in the rare event of a bad update.
Data residency – A region resides within the same geography as its pair (with the exception of Brazil South) to meet data residency requirements for tax and law enforcement jurisdiction purposes.