The rise of virtual machines in the data center was one of the key developments that eventually led to the telcos’ exploration and implementation of network functions virtualization. But now some are talking about using Linux containers as an alternative or additive to VMs in service provider NFV architectures. And a company called Docker is playing a leading role in this movement.

Linux containers promise better performance, portability, and speed than VMs, says Scott Johnston, senior vice president of product at Docker, the first entity to make Linux containers widely available and usable. Because Linux containers are not as large as VMs, he explains, network operators realize a 10:1 performance improvement plus better speed. The down side of Linux containers, however, is that you’re trading API and application complexity for those benefits because more containers equates to more things to manage.

Containers are also 100 percent portable, he adds, so when a developer writes an application on a container, that app can be moved from a laptop, to a data center, to the cloud – and all that can happen without altering the app in any way. It essentially makes good on the write once, run anywhere promise made by another software company years ago. And by enabling this portability, Johnston suggests, Linux containers help drive new service creation and innovation, which is what the carriers’ move to NFV and software-defined networking are supposed to be all about, at least in the long term. (Cost savings being the short-term goal.)

“Typically when talking about OpenStack, users think virtual machines, so a certain amount of overhead,” says Wim Coekaerts, senior vice president of Linux and virtualization engineering at Oracle (News - Alert). “The appeal of containers (and Docker) is the zero overhead isolation, which makes it very attractive..... Docker is in general something a lot of developers and software providers find interesting as a packaging and distribution model of their applications.”

Big telcos could also avoid VM licensing costs by leveraging Linux containers, says Johnston of Docker, but he adds that is part of a longer-term discussion.

While it’s possible to run Linux containers on bare metal servers, without VMs in the mix, Johnston says, Linux containers can also be used in concert with VMs. In fact, some enterprises are running containers on top of VMs today, he says.  

Phil Tilley, director of NFV and CloudBand marketing for Alcatel-Lucent (News - Alert), says Linux containers may be a better match for lightweight applications such as Triple A (authentication, authorization, and accounting) and DNS. Meanwhile, he says, kernel-based virtual machines address the heavyweight applications like IMS that the service providers are working to address now.

The container approach, Tilley adds, doesn’t require a hypervisor – the container runs directly on Linux. That creates some challenges, such as the fact that you don’t have isolation, he says.

“With containers you need to make sure your application works directly with a Linux kernel,” Tilley says.

But Tilley’s primary concern with Linux containers seems to be around its potential to push the forward movement the carrier NFV ecosystem has already made around VMs and hypervisors off track.

“Right now we’re making good progress with NFV, and the management and orchestration layer within NFV is being defined, and that’s working around hypervisors and KPM,” says Tilley. “And I think it’s important we continue down a path to get some headway…. The danger is if we get off the track we will lose momentum.”

Whatever the potential downsides to Linux containers, this is a movement that seems to be gaining momentum. Heck, even VMware has gotten on the Docker bandwagon, having announced integration with Docker on its VMware Fusion, VMware vCloud Air, and VMware vSphere products in December.

Although VMs and hypervisors came first in the carrier NFV and OpenStack discussion, Docker was part of the bulk of discussions at the most recent OpenStack Summit; there are now the Nova plugin and Heat driver for Docker; and several service providers are already doing proof of concept work related to Docker and Linux containers, says Johnston of Docker.

Swamy Vasudevan, CTO of cloud, SDN, and NFV for Ericsson (News - Alert), says that when NFV appeared on the scene, all implementations were focused around OpenStack and VMs in a move to emulate what Amazon had already achieved with its Amazon Web Services (News - Alert) architecture. Now operators are taking a step back because that method is taking a long time to deliver what they want, Vasudevan adds, explaining that the container approach leverages a single OS and one instance but is still scalable and more dynamic.

In fact, he says, Facebook and Google (News - Alert) already use containers in some of their applications, and some of the tier 1 service providers in the last three to four years have been sending their people to Silicon Valley to find out more about those operations.