Suddenly, it seems, everyone loves Docker.
It wasn't so long ago that people were talking about Docker as a potential "threat," or at least a competitor, to server virtualization technology. Could it be that Docker was bad news for hypervisor makers in general, and VMware — as the largest commercial server virtualization technology vendor — in particular?
But at VMworld in August VMware announced that it was integrating Docker containers into the VMware suite. "Our joint collaborations with Docker … are all about enabling our customers to get the benefits of containers, whilst taking advantage of the unique capabilities of VMware's Software-Defined Data Center approach," said VMware's Paul Strong at the time in a blog posting."
Not to be left out, it seems that the Xen Project loves Docker too. Olivier Lambert — who is closely connected with the Xen Project — published a blog posting recently entitled "Xen & Docker: made for each other." Isn't that nice?
Here's the deal. Lambert notes that developers are increasingly using Docker running inside VMs so that they can "develop and deploy a variety of applications with incredible efficiency, while virtualization eliminates any constraints and/or exposure to outside attacks."
Doing so provides a kind of best of both worlds approach to application development, he reckons. You get the fast boot times, light weight and high container density on one host that Docker offers, but running the containers in a virtual machine means the developers can muck about to their hearts' content without breaking anything or bringing down any machines — apart from the VM that's running their Docker containers.
"The VM is actually a sandbox, not a jail; developers can create their containers as they need in this scenario," he points out.
But if developers are to play in this sandbox productively, they need a tool to help them do so, he argues. And that tool is – or shortly will be – Xen Orchestra, a web interface to XenServer (or in fact any host with Xen and XAPI), which Lambert created.
What you can do with Xen Orchestra today is adjust the number of CPUs, and the amount of RAM and other resources that a VM has at its disposal, while it is running. You can also use Xen Orchestra to take snapshots of your VM. "When your fresh Dockerized VM is ready, take a snapshot. Then you can roll back when you want to retrieve this clean state," says Lambert. That means an admin can reset a VM running Docker easily whenever it gets messed up by pesky devs with dodgy code.
That's all well and good, but wouldn't it be better if the devs could do this, rather than bothering overworked admins?
The good news is that's on the roadmap for Xen Orchestra as well, along with a couple of other features:
ACLs and delegation: ACLs will be integrated into Orchestra allowing VM delegation to Docker users. That means they'll be able to roll back or reboot their Docker-running VM every time it falls over.
Docker-ready templates in one click: Lambert also outlines the capability to request a Docker template directly from the Orchestra interface. "It will be downloaded and operational in your own infrastructure, with a Docker listening and ready for action, in the resources you choose to allocate (CPU, RAM, Disk). No installation: it works out of the box," he says.
Finally he also (almost) promises Docker control from Orchestra. "Because we can get the IP of a VM thanks to its Xen tools, we should be able to send commands to the Docker API directly through XO. In this way, you'll just have to use one interface for Docker and Xen (at least, for simple Docker operations).
So there you have it. If you are into server virtualization technologies, Docker is your friend. And you can expect it to play nicely with your existing virtualization technology infrastructure — because virtualization infrastructure developers are terrified of people turning their back on virtualization if it doesn't.
Paul Rubens is a technology journalist and contributor to ServerWatch, EnterpriseNetworkingPlanet and EnterpriseMobileToday. He has also covered technology for international newspapers and magazines including The Economist and The Financial Times since 1991.