If you read about SDN, it won’t be very long before you read about multi-tenancy. While this word is often used, there haven’t been many discussions about what it means, and it turns out it means different things to different people. It’s an important concept so I thought I’d blog about it and get your comments and reactions.
For service providers, it’s very straightforward. As SP’s sell their services, each customer becomes a “tenant”, renting compute, storage, networking and related services for their individual needs. Originally this was done by renting space by the square foot inside of a colocation facility, and the customers would roll in their own equipment and take advantage of the facility’s internet connectivity and other services. In some cases tenants were (and still are) actually separated by chain link fence. It’s easy to see why you’d call them “tenants”.
We can’t talk about tenants without mentioning “Coke and Pepsi”. If tenants are sharing any part of the infrastructure, they must be confident that their data is being protected from their neighbors; so for example Coke can’t gain access to Pepsi’s data and vice versa. This is an essential feature for any shared environment, and a prerequisite to using public facilities.
Today most data centers have adopted server virtualization to consolidate large numbers of lightly used servers to fewer, more highly utilized servers, thereby dramatically improving costs. This is as true for service providers as it is for dedicated enterprise data centers. In today’s world of virtualization, providers are offering virtualized compute capacity, and customers no longer need to be allocated specific machines, but instead can take capacity from wherever it is available at that instant. We call this way of offering services the public cloud, and it’s growing fast as customers realize how flexible and cost effective it can be.
In the public cloud, you need the same kind of customer separation as in the physical colocation world, but providing that separation gets more difficult, and providing enough proof to gain customer confidence is also more difficult. After all, you can see a chain link fence, but you can’t really see a VLAN.
So – if you’re a service provider offering virtualized capacity, you can use VLANs to separate customers, but VLANs are limited. There are only 4,095 to begin with, so for a provider wanting to support hundreds of thousands of customers VLANs are not going to work. Thus VXLAN was created, to extend the scale and to provide infrastructure that could be more easily programmed and provisioned per-tenant – a foundational principle for SDN.
Tenement – early multi-tenancy ?
Back to my original question – what is a tenant?
For service providers the answer is easy to see, but the real power of SDN will be its application to enterprise data centers. Service providers are the early adopters, as they need to drive costs down and flexibility up in order to compete.
But enterprise architects that I’ve talked to are eager to adopt the same model, to become more responsive to their internal customers. These are visionary IT leaders, and they can see an environment in which departments can self-provision compute, storage and networking resources from the central IT pool, while IT can ensure that their security, compliance and other policies are enforced. IT becomes an internal service provider. In this case, the tenant can be a combination of several things – departments, business units, applications, or even separate parts of complex applications. As SDN becomes more mature we expect to see massive adoption of this “multi-tenant” enabling technology in internal IT. The benefit is a much more agile, responsive IT, able to create complex compute capacity on demand.
What do you think? Do you see your enterprise adopting a service provider approach to support your internal tenants? Why, or why not?
Josh tells me the comment feature is working – I need proof. Talk to me!
How do you prepare for a multi-tenancy infrastructure? We will be exploring support of networking in a multi-tenancy environment in a series of webinars. You can find them at: