With VMware Cloud on AWS (VMConAWS) you can consume an SDDC-as-a-service that contains vSphere, vSAN, NSX and HCX. By default VMConAWS provides an SLA of 99,9%, this can be increased to 99,99% by implementing a stretched cluster configuration. Take into account the specific FTT requirements that apply based on the number of hosts per site and the stretched cluster configuration, more details in the Service Level Agreement for VMConAWS.
With this option a vSAN stretched cluster configuration is deployed, half of the hosts in a cluster are deployed in an availability zone (AZ), the other half in the second AZ and the witness node is deployed in the third AZ.
In this scenario vSAN is stretched, NSX segments are stretched while HA and DRS will take care about redistributing your workloads after a site failure. The RPO for a stretched cluster configuration is 0 because of synchronous replication, while the RTO depends on HA restart times.
Update on pricing
At VMworld Europe a price reduction for stretched clusters on VMConAWS was announced:
VMware is now announcing up to a 16% reduction in price for a Stretched Cluster deployment – we are eliminating the add-on charges for Stretched Clusters software – this will result in cost savings of ~9% for an on-demand purchase of a stretched cluster, ~12% for a 1-year subscription and ~16% for a 3-year subscription.
These add-on charges had to do with the extra management efforts and extra systems that are required to run a stretched cluster.
Earlier this week another price reduction was announced, this one is regarding the cross Availability Zone (AZ) data charges. Let’s first look how cross AZ data charges were originally applied:
The stretched clusters feature synchronously replicates data between Availability Zones. Since these data transfers go across AZs, they will incur AWS intra-region data transfer charges in each direction (e.g., when you write data from AZ1 to AZ2, and the intra-region data transfer charge is $0.01/GB, it implies that each GB of data exits from AZ1 and enters AZ2, so there will be data transfer charge for exiting AZ1 and entering AZ2 which will sum up to $0.02/GB). These AWS charges are additional and are part of your VMware Cloud on AWS bill. Please see AWS pricing page for intra-region data transfer charges.
So, like with any other cloud, AWS charges you for certain network traffic based on the amount of generated traffic. These costs are on top of the regular costs for running your SDDC. Some data charges costs are paid by VMware (and charged back to the customer), some data charges are paid directly to AWS.
The following diagram, created by my colleague Gilles Chekroun, provides some additional details on this:
Additional information on the cost structure is available in this article at gilles.cloud. As you can see, cross-AZ data charges are around $0.01/GB (note, these prices are specific to the AWS region and you have to deal with exiting and entering costs); the costs also apply to vSAN synchronisation traffic in a stretched cluster architecture.
Earlier this week the following announcement was made around cross AZ network fees:
We are excited to announce that we are now offering a 95% discount on the Cross AZ network fees resulting from Stretched Cluster operations! This is expected to be available in VMware’s Fiscal Q4’2020 and effective dates will be announced at availability (source).
Concretely this means 100 GB of cross-AZ traffic would have cost $2.00, this will now cost $0.10 (for the 100 GB in this example). Hopefully this will make the decision to use a stretched cluster even easier :).
More details around this announcement are available here.