When I deploy 1 VM on multiple zones in same region, will one VM replicate to other VM automatically? If not how does this help for high availabliity? And how replication can be configured?

Question

For a requirement of resiliency/High Availability can zone redundancy be considered as single solution or it has to be VMSS or ZRS with some more configuration?

Answer 1

VM deployment across availability zones When you deploy a single VM across multiple availability zones, it does not automatically replicate to another VM. A VM resides in a specific zone, and if that zone experiences an outage, the VM will go down unless additional measures are taken.

How availability zones improve high availability Availability zones help with high availability by allowing you to deploy multiple VMs across different zones. This setup ensures that if one zone fails, other VMs in different zones remain operational. A load balancer is typically used to distribute traffic among these VMs.

Configuring replication across zones Replication is not automatic for individual VMs. To enable redundancy, you can use:

• Azure Virtual Machine Scale Sets (VMSS): Automatically distributes VMs across zones and provides scaling and load balancing. Note this doesn't actually "replicate" their content - but rather makes sure that every VM you deploy is configured the same way.
• Azure Site Recovery (ASR): This does support ongoing replication from one VM to another VM in a different availability zone for disaster recovery, but failover is manual.

Is zone redundancy enough for high availability?
Zone redundancy alone is not a complete solution. For full resilience, you'd need to take additional steps. Details depend on the workload running on your VMs. For example, for database management solutions like SQL Server or SAP HANA, you can use database native-replication. With VMSS, you'd also want to use a load balancer to distribute load or provide failover capabilities. Azure Site Recovery could be used for disaster recovery (not HA). VMSS ensures automatic scaling and failover and a load balancer ensures traffic is directed to healthy VMs.

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hth

Marcin