Recently, I worked on a project to deploy for a customer vCloud Air Disaster Recovery. Along the way, as mentioned in a previous post, I went ahead and picked up the applicable VMware certification for it. I wanted to discuss how vCloud Air works. To begin with, I wanted to discuss the two offerings, and how they interact.
vCloud Air OnDemand
vCloud Air OnDemand is a public cloud Infrastructure As a Service (IAaS) solution. You can run pretty much whatever workloads you like. These are VMs or appliances you deploy either manually by yourself, using their catalog, or perhaps even upload templates from your VMware on premise environment.
vCloud Air Disaster Recovery
vCloud Air Disaster Recovery is a public cloud Infrastructure As a Service solution. It’s identical to vCloud Air OnDemand except it’s geared specifically for failing over replicated virtual machines. VMs you run in this cloud can only be replicated virtual machines from your vSphere environment. These VMs are replicated with vSphere Replication. In addition, you can designate isolated networks within vCloud Air DR for isolated testing.
Two Separate Clouds
One design concept to understand is vCloud Air OnDemand and vCloud Air Disaster Recovery are two completely separate clouds. While they have very similar features and management interfaces, they are completely independent and separate. This is so much so that in order for VMs in either to be able to communicate with each other, you must setup site to site VPN connections between them. Keep this in mind.
When Should I Use vCloud Air OnDemand vs Disaster Recovery?
This seems obvious, right? If you want to replicate VMs using a whole VM replication technology and fail VMs over, use DR. Use OnDemand when application or service data will replicate natively instead of whole VM replication.
But it’s not so simple as that. What if a VM has the ability to replicate within its service or application? Do some services and replication prohibit you from using whole VM replication?
The giant elephant in the room for DR solutions when asking these questions is Active Directory. If you want your DR solution to be wholly independent, you likely need domain controllers in the cloud and on premise. And it’s not supported to use whole VM replication with Active Directory Domain Controllers. So, DCs are out for use with vCloud Air DR for production use cases.
Generally speaking, it maybe a bad idea for infrastructure bread and butter type VMs generally speaking. For example, DHCP servers could be replicated, but the problem is vSphere Replication can only configure VMs with as low a RPO as 15 minutes, and going over a WAN link might make that 15 minute RPO at best impossible with all your other VMs you’re replicating. Perhaps it would be better to build a VM within OnDemand and run a script to export the DHCP database regularly to the DR site.
Bottom line though is this: You only need OnDemand if you won’t replicate VMs using vSphere Replication to vCloud Air. If you want to run replicated VMs within vCloud Air as a DR solution, AND you want to ensure that the vCloud DR site is not dependent at all on your on premise infrastructure, you probably need both if only to facilitate running Domain Controllers. Perhaps other services and applications you’ll replicate data to through other means, too.
It would look something like this: