But the virtualisation giant may follow up that move -- made in support of a new PaaS (platform as a service) cloud-computing strategy -- by investing in distributed caching technology, a class of middleware that boosts application performance and scalability.
"The most glaring omission [in VMware's portfolio] is [the] need for Java object distributed caching to provide yet another alternative to scalability," Ovum analyst Tony Baer said in a post to his personal blog on Tuesday. "If you only rely on spinning out more [virtual machines], you get a highly rigid, one-dimensional cloud that will not provide the economies of scale and flexibility that clouds are supposed to provide. So we wouldn't be surprised if GigaSpaces or Terracotta might be next in VMware's acquisition plans."
Distributed caching technologies store data needed by applications in memory across a pool of servers, instead of reading it off disks, resulting in supercharged performance.
But the market for such systems -- populated by smaller companies like GigaSpaces as well as Oracle and IBM -- remains fairly small, and they can be complicated to configure and manage.
Still, another close watcher of the middleware market agreed with Baer's assessment.
"It would make absolute sense for VMware to buy a [distributed caching platform] vendor," Gartner analyst Massimo Pezzini said via e-mail.
"I think one of the reasons why VMware is buying SpringSource is to be able to move up the food chain and sell cloud-enabled application infrastructure on top of their virtualisation infrastructure," Pezzini said. "It wouldn't take much to make it possible to deploy Spring on top of the bare VMware -- i.e., with no Linux or Windows in the middle. Therefore, they would absolutely need a mature DCP as the underpinning infrastructure for elasticity, data distribution, fast messaging across nodes, et cetera.
"Developing one takes forever, whereas GigaSpaces would be a perfect fit given it is already integrated with Spring," Pezzini added.
Geva Perry, a former GigaSpaces executive who now blogs and consults on cloud-computing issues, echoed Pezzini.
SpringSource is very strong in regard to developer tools but "the weakest part of their picture [is] the runtime environment," where technology like GigaSpaces could play a key role, he said.
Terracotta may also be a fit, especially given the fact that it recently made a cloud-computing-themed partnership announcement with VMware.
A VMware spokeswoman declined comment, saying the company does not respond to industry rumors or speculation. Terracotta and GigaSpaces couldn't immediately be reached.
Meanwhile, another observer isn't convinced VMware actually has such a purchase on its mind.
"This speculation makes sense if we believe that VMware-Spring must be configured like IBM, Oracle, and Red Hat," said Forrester Research analyst John Rymer via e-mail. "This is an open question. I am not convinced that VMware will now embark on a middleware acquisition spree. Both VMware and Spring were winning without having to own a complete middleware stack, and the combined companies don't have the sales horsepower to compete with IBM, Oracle, and RH on those companies' terms."