containers

It seems I've had a lot of questions about OpenVZ container migration lately on the #openvz IRC channel on the Freenode IRC network. While I made a silent screencast on that topic a few years ago, I thought it was time for a refreshed one so here it is. Enjoy.

What is an OpenVZ container? It is a form of virtualization where you can create a type of a virtual machine called a container that is basically a strongly isolated chroot environment with device and resource management features.

What is migration? It is the ability to easily move a container from one physical OpenVZ host to another. Live / online migration allows for no downtime and maintains existing network connections. Offline migration stops the container on the original host and starts it up on the destination host and as a result the containers uptime is reset and existing network connections are dropped. Watch the screencast for all of this in action.

You can also download this directly if desired. right-click, save link as:
openvz-vzmigrate.webm (12.8 MB)

I like to do some walking on Sundays. Walking is what us older people do for exercise. When I walk, I like to listen to audiocasts. One of the programs I've been listening to with some regularity is FLOSS Weekly and the program this week was about OpenShift.

OpenShift is a Platform as a Service (Paas) product that is, as you would expect, built on top of Linux. What is PaaS? System Admins / DevOps are constantly deploying web-based applications. They all use a web server, a database, a scripting language / runtime environment, etc. PaaS automates most of the common tasks needed so you don't have to do the same thing over and over... and can concentrate more on your application.

OpenShift has been available for awhile now as a developer preview service run by Red Hat on top of Amazon Web Services (AWS). Supposedly the current level of service will always be free but they plan to charge for higher levels.

A few weeks ago they released OpenShift as open source project (OpenShift Origin) with an Apache license and no code contributer agreement needed.

Turns out that they have various combinations of things available such as several databases to pick from, several scripting languages, etc. Those things are called "cartridges". Some of the cartridges they have are:

Databases: MySQL, PostgreSQL, and mogoDB
Language runtimes: Node.js, Perl, PHP, Python, Ruby, and Java / JBoss
Frameworks: CodeIgniter, CakePHP, Ruby on Rails, Django, Perl Dancer, Flask, Sinatra, Tornado

Need a libary of web-applications to pick from? OpenSift has "quick-starts" which are pre-packaged web-applications. Included are such things as WordPress, phpMyAdmin and Jenkins.

Another concept they have is a "gear". A gear is really an LXC container. Why they needed to create a new term (gear) rather than just calling it a container, I don't know. So it appears that Red Hat is using Linux native containers (LXC) in a product now... so I hope they'll get more into containers... since I'm a big container (mostly OpenVZ) fan. Dependong on how heavy a particular cartridge is, it may or may not be deployed inside its own gear. They easily fit serveral dozens to a hundred or more gears on each cloud-based virtual machine. While Red Hat runs their service on top of AWS, users are free to create their own setups on top of whatever virtualization platform they want.

OpenShift is written in Ruby but also uses some shell scripts for cartridge and gear operations. What OpenShift does could probably be mimiced with containers that use a large set of OS / Application Templates but the unique feature that makes OpenSift stand out is that it uses git for deployment.

If any of this interests you, check out either the FLOSS Weekly audio version or the video. Unfortunately, they only seem to support patent encumbered codecs.

I'm not familiar enough with Ubuntu Development to know just how far this might go but at the very least it appears that some Ubuntu developers have identified as a goal to make LXC usable for production stuff and to put it on par with KVM.

How to make LXC ready for production?

The linux container tools (http://lxc.sourceforge.net) raised some interest for the community but there are crucial functionalities which are missing. The purpose of the session is to identify these missing functionalities and prioritize them in order to have a ready for production component for the Natty server delivery.

CloudServerNContainersFinetune

Make the use of containers for service segregation on par with KVM in terms of functionality and transparancy.
[...]
Joe is a system administrator who wants to start a temporary image to run postfix. To save on resources he runs it using a container. He wants to be able to update the image without fear of updates un-doing hacks needed for containers.

Jane is a system administrator who wants to be able to mix containers with KVM VMs through libvirt. She wants libvirt to auto-start containers, and virt-manager to cleanly shut down the containers.

So far I see identification of problems and need for various features... and a LOT of "todo" lists. I hope they get a significant chunk of that accomplished... so that it can filter back upstream and be used by other distros too.

I'm a long time reader and subscriber to LWN (Linux Weekly News). LWN is probably the best Linux news site out there with regards to covering kernel development and I often find myself eating up considerable amounts of time sifting through their articles. This week they had an article covering some recent progress in the mainline kernel on checkpointing and restoring of processes and containers of processes... and I wrote a somewhat lengthy response that I decided to share here. I would link to the LWN's original article but it won't be anonymously accessible until next week.