on premises for a variety of reasons. There are important items to consider prior to migrating these VMs back and strategies for migrating risk.
Reasons to migrate cloud VMs
The most common reason for moving cloud VMs back on premises is probably “bill shock.” This usually occurs because the promotional rate pulls organizations in, but the real rate ends up being significantly higher than forecasted.
Other reasons to move back include local data retention laws and corporate risk mitigation strategies. There are also customers who choose to migrate cloud VMs back on premises because the cloud doesn’t live up to their expectations. Unused development hosts can also end up being tremendously expensive if they aren’t properly monitored.
Before even thinking about a reverse migration, there are a number of nontechnical items that you need to consider.
First, what does your contract say regarding early termination or leaving the cloud provider? This is more of a problem with smaller cloud service providers than with Amazon Web Services, Azure or Google, but it’s worth checking, irrespective of provider.
Also, check your licensing. An administrator can’t just migrate a cloud VM back on premises and continue using the VM as if it still existed in the cloud. Prior to the migration, you need to check both the OS and application licensing small print. Be smart; get that confirmation in writing. Most likely, you’ll find that different licensing rules apply.
If you’re trying to migrate a platform-as-a-service (PaaS) offering back to your data center, you need to have all the PaaS dependencies lined up.
Another potential expensive pain point is provider egress charges. Most of the large cloud providers charge per megabyte for egress of data. If an administrator is moving many terabytes of data, the egress cost could be very substantial. As an example, Amazon charges $0.090 per gigabyte.
Performing the migration
The hurdle of migrating cloud VMs back to site can be very difficult depending on the provider. When moving back to a VMware on-premises environment, you have to use the VMware converter tool to recreate the VMDK files.
Depending on the size of the VMs, this could take a long time. It really depends on network capacity. Also, each VM would incur a minimum of several hours downtime as the conversion process from cloud back to premises would have to be performed while the server was powered off if using the converter.
With Azure, this process is slightly easier because Azure and Hyper-V use the VHD disk format. Simply put, this means that migrating the actual machine — excluding networking, Active Directory (AD) and so on — becomes as easy as using the web browser to download the VHD files and attaching them to a new VM that has no disks. While this may work for a handful of servers, the technique wouldn’t scale if an administrator was trying to move more than a few servers back to the local data center.
There are several tools you can use to migrate cloud VMs back on premises. These include Zerto and several other disaster recovery (DR) and replication software providers. The great thing about using products like Zerto is that they remove the need for extra conversion steps, which means no messing with disk conversions and copying disks manually.
The real upside is that it also allows an administrator to significantly reduce downtime because these products perform continuous replication. After the initial synchronization back to premises, the cutover can start. The end result is massively decreased ingestion time and failback capability. That does, however, leave the administrator to configure the network, AD and other application dependencies, which can be a trial in its own right.
In summary, moving cloud VMs back on premises is possible, and there are tools that can help minimize the complexity and downtime of the migration. The migration is the easy part. Working out the licensing costs and egress costs is the difficult part. I would advise anyone that’s looking to migrate back to a local data center to first look at the type of tools mentioned above. While they might not be cheap, they will greatly simplify the migration process. When the administrator completes the job, the licenses can be recycled and used for DR purposes.