Dennis Howlett has summarized the story so far in a debate I was having these past few days with Josh Greenbaum, Bob Warfield and assorted other Enterprise Irregulars (and it's not the first time I've debated multi-tenancy). But everyone still seems to overlook the key issue about multi-tenancy, the one factor that makes it an essential prerequisite to demand as an enterprise buyer if you're shopping for a SaaS or cloud solution.
Maybe people miss it because it's so obvious, or perhaps it's because the significance is not yet self-evident. When something changes the landscape so dramatically, it sometimes takes a bit of imagination to see how it will all pan out. Back in the early days of the automobile, who would have foreseen the networks of high-speed roads, the filling stations and the mass production that were going to make this a faster, cheaper, more convenient form of transport than the horse and the railroad?
Today, people look at cloud computing and yet completely overlook the role of the cloud itself in making it what it is. What if early motorists had only ever wanted to drive on their own private land? Automobile innovation would have peaked with the golf buggy. Private clouds and single-tenant SaaS applications are just as limited, and that's why multi-tenancy matters. Yet even Bob Warfield, who's on my side of the argument, can write, "There are two primary advantages to the Cloud: it is a Software Service and it is Elastic." The cloud has a crucial third advantage, and it's no coincidence that it shows up later in the same blog post at precisely the point when Bob is explaining why multi-tenancy matters:
"What would an app look like if it was built from the ground up to live in the Cloud, to connect Customers the way the Internet has been going, to be Social, to do all the rest? Welcome to SaaS Multitenant."
Multi-tenancy matters because it's the ideal architecture to make the most of the public cloud environment. The cloud matters because it's where all the connections are. That's where your customers, your suppliers, your partners and your employees are, along with a wealth of other resources from all around the world. Multi-tenancy provides the best possible platform for interacting in real-time with all of those resources (which is why top online properties like Google, Facebook, Amazon, eBay and others are completely multi-tenant). But more than that, a multi-tenant application runs on a shared platform that is constantly being fine-tuned to succeed better at those interactions.
Multi-tenancy benefits enormously from the magic of something I call collective scrutiny and innovation. When hundreds or even thousands of other businesses are using exactly the same operational infrastructure, all of them benefit from each of the different ways in which they're challenging and stretching that shared infrastructure. All of them have access to the newest functionality that's introduced at the behest of the early adopter minority. All of them benefit from the hardening of the infrastructure after any of them come in contact with a newly detected threat.
The strength of multi-tenancy is that each of its multitude of individual tenants keeps it constantly evolving. This is in direct contrast to single tenancy, the whole point of which is to limit evolution only to those changes that are perceived to directly benefit the individual tenant. Thus single tenancy misses out on innovations and other advances that are being adopted by competitors, partners and third-party services. If everyone were unconnected that may not matter so much but it's hugely important in the cloud, where you may only realize the significance of a new capability when you see it linked up with other resources.
This is before we even start to think about the potential for using pooled aggregate data for benchmarking, validation or trend analysis, along the lines that Dennis Howlett discussed in his weekend blog post. Most of the benefits of public cloud multi-tenancy have not even begun to be explored, much as the huge transformative impact of the internal combustion engine was unimagined at the beginning of the twentieth century.
That's probably why, for now, it may look as though the choice between multi-tenancy and single-tenancy is something that matters only to the vendor. In truth, multi-tenancy matters even more to buyers, because it's what makes the difference between a SaaS application that's destined for rapid obsolescence and one that will continue to evolve with the cloud and all the wealth of possibility that's opening up in the connected Web.