If you thought virtual appliances - complete ready-to-run services in (typically) a VMware wrapper - were just for trying things out on, think again.

So says Dave Asprey, the VP in charge of technology strategy at Zeus Technology, which announced a virtual version of its ZXTM traffic manager last year. Asprey says that sales of ZXTM virtual machines (VMs) now exceed those of traditional hardware appliances, and are closing on the sales of ZXTM as a straight software app.

"We had assumed that virtual appliances would mostly go in to test and so on, then they'd put in a full appliance, but we have found people happy to deploy a VM in production," he adds.

"A customer can download our stuff and have it running in 20 minutes - it's so much faster than shipping a demo box. It's more scalable once sold too, as you can just download another licence."

The virtual approach is attractive partly because of its relative simplicity, he says. "IT knows how to deploy and lock-down an OS, and how to deploy apps, but it's still more work than deploying a VM. And the performance hit from virtualising isn't as bad as you might think - you can get a couple of Gigabits through a VM, and few companies actually have Gigabit pipes."

Another advantage of the virtual approach is that the virtualisation framework - the hypervisor - insulates the VM from the hardware, says Steve Harriman, marketing VP for network monitoring specialist NetQoS. That means there's no need to worry about whether a customer's server will be up to the job of running the software - as long as it's running the right hypervisor, it will run the appliance.

"Our eval units are now being shipped in VMware, and we are planning to roll it out in production where the customer has multiple units and wants to reduce the hardware count," he added.

Other suppliers offering virtual appliances include Covergence, with VMware-wrapped session border controllers for unified communications, and Kace, which has a VM version of its systems management box.

"We developed a purpose-built box to manage networks," says Rob Meinhardt, co-founder and CEO of Kace. "Now we also offer KBOX in the format that can run inside VMware as part of a customer's overall virtual environment."

The common thread here is of course VMware, although as Dave Asprey acknowledges, that is far from being the only hypervisor on the market. He says that the basic concepts are common to all the hypervisors.

"VMware has the first-mover advantage but we use both VMware and Microsoft Virtual Server, as SMBs often don't have VMware," he explains. "The key thing is manageability - for the SMB, Virtual Server looks just like a Windows server. Xen might come up in the next nine months, if we start hearing calls for it, and when customers ask for Virtual Iron or Virtuozzo, say, it will be relatively simple to do it."

Steve Harriman agrees. He points out too that while other virtualisation schemes may be cheaper than VMware, the virtual approach isn't about saving money on software or hardware - 1U pizza-box servers aren't expensive, either - it's about simplifying installation and management.

He adds, "VMware's not necessarily cheaper than physical hardware. It's not the cheapest way of doing it, but it's the supported way.

"A VM can also come into play when the customer has multiple products - we'd love to just ship software, but network admins don't want to run and troubleshoot general-purpose servers, they want appliances. It's useful for support as well, it's a fixed configuration so we know what's running."

And there's more, according to Dave Asprey. He says that in the future, virtual appliances - and virtualisation in general - will play a vital part in making IT systems more autonomic, enabling them to self-heal and do their own load balancing.

"Lots of companies are looking to make their data centres more self-administering," he adds. "We can report via SOAP when the system is loaded and call for more resources - the future of management systems is autonomic, and it's all about SOAP."

Does that mean it's a slippery topic? Perhaps, but one thing is certain - virtual appliances are here, and they're here to stay.