Tag Archives: devops

Fedora for short-lifespan server instances

I read Máirín Duffy’s coverage of the Fedora Board’s userbase discussion. Really interesting. I wanted to add my take.

tl;dr: Puppet/Chef make Fedora’s short support period much less of an issue.

The OS is a building block

I’ve been watching a lot of videos on DevOps lately. Several close friends of mine are sysadmins and I’ve been learning a lot from them about the transformation that their profession is undergoing. From this year’s ChefConf, Adam Jacob’s keynote and the talk by Sascha Bates really impressed on me the big change in how admins should view machines — They’re not permanent, or even semi-permanent. They are ephemeral snowflakes that may live a year, or just an hour, so don’t get too attached.

Part of why admins like VMs is because the isolation they provide between different services. I used to run mail, DNS, and httpd from a single machine. Everything was mostly separate but not quite everything. They had separate userids but everyone’s config was in /etc, even touching the same files, sometimes. A full disk affected everybody. /var/log/messages didn’t split up their logging cleanly (by default, anyway.) It all just was built assuming there would be an admin at a command shell who could use their brain to resolve the conflicts to make everything play nice on a single OS image.

One service per instance

Admins adopted VMs for isolation, increased density, and better per-service resource allocation, but then ran into other problems. The setup that they did by hand once per new-hardware now was once per instance. (Editing /etc/sudoers for the fiftieth time gets old.) The tools then evolved further, until today one may keep no persistent state in an instance. Now, an instance is kickstarted into existence and configured automatically for the one job it will ever do. The sysadmin’s job isn’t to herd boxen any more, it’s to build ’em, run ’em, and then reap ’em.

All the OS mechanisms for co-existing server processes, they’re now either obsolete or vestigial to some degree. What is important is the malleability of the OS to assume all the tasks it may be asked to – rather like a stem cell needs to be able to become a nerve or muscle, but never needs to be both.

Never upgrade, just redeploy

Let’s come back to the odd fact that Fedora is both a precursor to RHEL, and yet almost never used in production as a server OS. I think this is going to change. In a world where instances are deployed constantly, instances are born and die but the herd lives on. Once everyone has their infrastructure encoded into a configuration management system, Fedora’s short release cycle becomes much less of a burden. If I have service foo deployed on a Fedora X instance, I will never be upgrading that instance. Instead I’ll be provisioning a new Fedora X+1 instance to run the foo service, start it, and throw the old instance in the proverbial bitbucket once the new one works.

Cheap and easy virt and config management gives admins what they’ve always wanted — stability when they want it (run a LT support distro image, or for the VM host) or the latest stuff for their fast-moving business-oriented instances, by running a fast-update or rolling-release distro.

What Fedora should do

We’re already working on some of these to some degree — I think we should try to do even more to ensure Fedora is useful for the fast-update instance role.

First, Fedora needs to be able to be small. Nobody’s going to read the manpages on a throwaway instance, nobody’s even going to run vi. Image size matters when multiplied for each instance. Can we get by without /usr/share/doc/* and its thousands of copies of the GPL text? Fedora seems pretty good but there must be more we can do.

Second, we need to ensure Fedora supports the packages people are really using these days. Latest Ruby. Latest OpenStack. Vagrant. Django. Chef. Puppet. All the weird JS stuff that’s popular now on GitHub. 🙂 Continue to improve packaging tools so it’s easier for new contributors to do their first package, as well as for long-time packagers to maintain more packages. And not just package for contribution to Fedora, but for admins to package for solely internal distribution. Like Sascha Bates stresses in her talk, packaging is a huge benefit to automation, but it does require effort. It can be easier.

Finally, I think we need to continue to look at how easy it is to configure and manage an instance of the OS, and tailor it more for automated configuration. I believe the key to this is adding programmatic interfaces where they are lacking. See my “All Plumbing needs an API” talk. Since we’re probably being configured by another piece of code rather than a person at the shell, we need clear, unambiguous programmatic interfaces with good error handling. Chef should not be calling cmdline tools and checking error codes, there should be a Ruby configuration library that natively controls the whatever-it-is directly! We want configuring Fedora to be fast, straightforward, and reliable.

Conclusion: Stable+fast-update is better than stable+self-built

Practically the whole history of Linux distros has been the conflict between stability and new features. With virtualization, one still must make this choice, but at a much finer granularity than before. If you’re going to re-instance within 6 months anyways, why manually build your latest-Ruby and whatnot to support your app on top of a stable distro image? Maybe just use Fedora for those.