For many businesses, there is appeal in so-called “hybrid” cloud, which pairs a company’s own on-premises server room or data center with an outside cloud provider so it can make use of both sets of resources as needed.

Gartner vice president and distinguished analyst Lydia Leong sees three major takes on hybrid cloud.

“First, AWS sees hybrid as being able to run enterprise-class workloads in AWS and have them comfortably co-exist and interoperate with on-premises workloads—until the enterprise gets smart and moves all of it to AWS,” joked Leong.

Second, Microsoft sees hybrid cloud as a situation in which “applications running on-premises benefit from cloud extensions and cloud applications benefit from tying into on-premises capabilities,” she added.

And third, most legacy tech vendors still classify hybrid as a model in which “most stuff continues to be on-premises but you can do some things in the cloud as well and claim they can help you with that,” she added.

To clarify: Public cloud comprises a massive stockpile of computing servers, storage, networking, and increasingly other services, all of which companies can rent from Amazon (AMZN), Google (GOOG), Microsoft (MSFT), or IBM (IBM).

For this, the customer typically pays by the hour for computing and by the amount of data they store. That’s an attractive proposition if they have a task that suddenly fluctuates with demand and outstrips their internal capabilities. Black Friday sales is one example of how hybrid cloud is typically used. A retail operation can quickly add public cloud capability to take care of the sales spike and then turn it off when sales return to normal levels.

That pay-for-what-you-use model is attractive because it lessens the need for companies to extend their existing data centers or build new facilities for what might be transient demands.

Given Amazon’s need to woo more corporate business, its rhetoric about hybrid cloud has changed, although its emphasis really hasn’t.

“We’ve had a strong belief … that over the fullness of time—ten to 20 years—relatively few companies will have their own data centers and those that do will have much smaller footprints,” Andy Jassy, senior vice president of Amazon said at AWS Re:Invent last week. But, he added, for regulatory reasons or the fact that they have old workloads that still work but are difficult to move: “they’ll definitely be running in hybrid mode for a while.”

So, while Microsoft offers Azure Pack to run little Azure cloud clones inside corporate data centers, businesses cannot run Amazon cloud technology in their own infrastructure. For some, the definition of hybrid cloud requires that the technology on both sides of the on-premises/cloud divide be similar, if not identical.

But Amazon has come up with lots of ways to make it easier to move company internal data into AWS. It has a software storage gateway that vacuums up corporate data and uploads it to AWS. And at Re:Invent it announced a tough-as-nails Snowball storage appliance that customers can use to physically drop-ship 50 terabytes of data to Amazon, tracking it all the way.

Snowball is evidence of this “give us all your data” mantra, said Ben Whaley, founder of Whaletech, a technology consultancy in Berkeley, Calif.

Amazon watchers say the bulk of last week’s Re:invent news, including a database migration tool to move Oracle (ORCL) or Microsoft databases into AWS and a new compliance checking tool, was all about easing the transition of private business data to Amazon’s public cloud. Ditto with earlier integrations with VMware (IBM), a corporate standard, said David Mytton, president of Server Density.

So Amazon’s real message is: Ok, keep running some stuff in house, but it won’t last forever. We’ll be seeing you. And it’s hard to argue with this given the company’s phenomenal growth rate. The company is on track to hit a $7.3 billion run rate this year, and year-over-year sales growth is 81%.

But what about being able to incorporate Amazon’s technology in your own data center a la Microsoft? Uh-uh, says Amazon. Asked if Snowball was a harbinger of an Amazon appliance that might sit inside a company, Jassy said no.

“We have no current plans to build hardware for customer data centers,” he noted.

But even some of Amazon’s biggest customer boosters would like some flexibility there. The last comment I heard leaving a customer roundtable last week was from Tom Soderstrom, CTO of NASA’s Jet Propulsion Lab, who said he would love to be able to run AWS technology in-house.

The debate over private, public, and hybrid cloud deployments and what should run where will be a hot topic at the Structure Conference next month in San Francisco, where executives from Microsoft, Google, VMware, and EMC (EMC) will be on hand.

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