On Docker and Kubernetes on CloudStack
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Docker has pushed containers to a new level, making it extremely easy to package and deploy applications within containers. Containers are not new, with Solaris containers and OpenVZ among several containers technologies going back 2005. But Docker has caught on quickly as mentioned by @adrianco. The startup speed is not surprising for containers, the portability is reminiscent of the Java goal to "write once run anywhere". What is truly interesting with Docker is that availability of Docker registries (e.g Docker Hub) to share containers and the potential to change the application deployment workflows.
Rightly so, we should soon see IT move to a docker based application deployment, where developers package their applications and make them available to Ops. Very much like we have been using war files. Embracing a DevOps mindset/culture should be easier with Docker. Where it becomes truly interesting is when we start thinking about an infrastructure whose sole purpose is to run containers. We can envision a bare operating system with a single goal to manage docker based services. This should make sys admin life easier.
The role of the Cloud with Docker
While the buzz around Docker has been truly amazing and a community has grown over night, some may think that this signals the end of the cloud. I think it is far from the truth as Docker may indeed become the killer app of the cloud.
A IaaS layer is what is: an infrastructure orchestration layer, while Docker and its ecosystem will become the application orchestration layer.
The question then becomes: How do I run Docker in the cloud ? And there is a straightforward answer: Just install Docker in your cloud templates. Whether on AWS or GCE or Azure or your private cloud, you can prepare linux based templates that provide Docker support. If you are aiming for the bare operating system whose sole purpose is to run Docker then the new CoreOS linux distribution might be your best pick. CoreOS provides rolling upgrades of the kernel, systemd based services, a distributed key value store (i.e etcd) and a distributed service scheduling system (i.e fleet)
Like exoscale, any cloud provider be it public or private can make CoreOS templates available. Providing Docker within the cloud instantly.
Docker application orchestration, here comes Kubernetes
Running one container is easy, but running multiple coordinated containers across a cluster of machines is not yet a solved problem. If you think of an application as a set of containers, starting these on multiple hosts, replicating some of them, accessing distributed databases, providing proxy services and fault tolerance is the true challenge.
However, Google came to the resuce and announced Kubernetes a system that solves these issues and makes managing scalable, fault-tolerant container based apps doable :)
Kubernetes is of course available on Google public cloud GCE, but also in Rackspace, Digital Ocean and Azure. It can also be deployed on CoreOS easily.
Kubernetes on CloudStack
Kubernetes is under heavy development, you can test it with Vagrant. Under the hood, aside from the go code :), most of the deployment solutions use SaltStack recipes but if you are a Chef, Puppet or Ansible user I am sure we will see recipes for those configuration management solution soon.
But you surely got the same idea that I had :) Since Kubernetes can be deployed on CoreOS and that CoreOS is available on exoscale. We are just a breath away from running Kubernetes on CloudStack.
It took a little more than a breath, but you can clone kubernetes-exoscale and you will get running in 10 minutes. With a 3 node etcd cluster and a 5 node kubernetes cluster, running a Flannel overlay.
CloudStack supports EC2 like userdata, and the CoreOS templates on exoscale support cloud-init, hence passing some cloud-config files to the instance deployment was straightforward. I used libcloud to provision all the nodes, created proper security groups to let the Kubernetes nodes access the etcd cluster and let the Kubernetes nodes talk to each other, especially to open a UDP port to build a networking overlay with Flannel. Fleet is used to launch all the Kubernetes services. Try it out.
Docker is extremely easy to use and taking advantage of a cloud you can get started quickly. CoreOS will put your docker work on steroid with availability to start apps as systemd services over a distributed cluster. Kubernetes will up that by giving you replication of your containers and proxy services for free (time).
We might see pure docker based public clouds (e.g think Mesos cluster with a Kubernetes framework). These will look much more like PaaS, especially if they integrate a Docker registry and a way to automatically build docker images (e.g think continuous deployment pipeline).
But a "true" IaaS is actually very complimentary, providing multi-tenancy, higher security as well as multiple OS templates. So treating docker as a standard cloud workload is not a bad idea. With three dominant public clouds in AWS, GCE and Azure and a multitude of "regional" ones like exoscale it appears that building a virtualization based cloud is a solved problem (at least with Apache CloudStack :)).
So instead of talking about cloudifying your application, maybe you should start thinking about Dockerizing your applications and letting them loose on CloudStack.
Published at DZone with permission of Mark Hinkle, DZone MVB. See the original article here.
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