Guix

Towards Guix for DevOps

Jakob L. Kreuze — 12. júl 2019

Hey, there! I'm Jakob, a Google Summer of Code intern and new contributor to Guix. Since May, I've been working on a DevOps automation tool for the Guix System, which we've been calling guix deploy.

The idea for a Guix DevOps tool has been making rounds on the mailing lists for some time now. Years, in fact; Dave Thompson and Chris Webber put together a proof-of-concept for it way back in 2015. Thus, we've had plenty of time to gaze upon the existing tools for this sort of thing -- Ansible, NixOps -- and fantasize about a similar tool, albeit with the expressive power of Guile scheme and the wonderful system configuration facilities of Guix. And now, those fantasies are becoming a reality.

"DevOps" is a term that might be unfamiliar to a fair number of Guix users. I'll spare you the detour to Wikipedia and give a brief explanation of what guix deploy does.

Imagine that you've spent the afternoon playing around with Guile's (web) module, developing software for a web forum. Awesome! But a web forum with no users is pretty boring, so you decide to shell out a couple bucks for a virtual private server to run your web forum. You feel that Wildebeest admirers on the internet deserve a platform of their own for discussion, and decide to dedicate the forum to that.

As it turns out, C. gnou is a more popular topic than you ever would have imagined. Your web forum soon grows in size -- attracting hundreds of thousands of simultaneous users. Despite Guile's impressive performance characteristics, one lowly virtual machine is too feeble to support such a large population of Wildebeest fanatics. So you decide to use Apache as a load-balancer, and shell out a couple more bucks for a couple more virtual private servers. Now you've got a problem on your hands; you're the proud owner of five or so virtual machines, and you need to make sure they're all running the most recent version of either your web forum software or Apache.

This is where guix deploy comes into play. Just as you'd use an operating-system declaration to configure services and user accounts on a computer running the Guix System, you can now use that same operating-system declaration to remotely manage any number of machines. A "deployment" managing your Wildebeest fan site setup might look something like this:

...

;; Service for our hypothetical guile web forum application.
(define guile-forum-service-type
  (service-type (name 'guile-forum)
                (extensions
                 (list (service-extension shepherd-root-service-type
                                          guile-forum-shepherd-service)
                       (service-extension account-service-type
                                          (const %guile-forum-accounts))))
                (default-value (guile-forum-configuration))
                (description "A web forum written in GNU Guile.")))

...

(define %forum-server-count 4)

(define (forum-server n)
  (operating-system
    (host-name (format #f "forum-server-~a" n))
    ...
    (services
     (append (list (service guile-forum-service-type
                            (guile-forum-configuration
                             "GNU Fan Forum!")))
             %base-services))))

(define load-balancer-server
  (operating-system
    (host-name "load-balancer-server"
    ...
    (services
     (append (list (service httpd-service-type
                            (httpd-configuration
                             ...)))
             %base-services)))))

;; One machine running our load balancer.
(cons (machine
       (system load-balancer-server)
       (environment manged-host-environment-type)
       (configuration (machine-ssh-configuration
                       ...)))

      ;; And a couple running our forum software!
      (let loop ((n 1)
                 (servers '()))
        (if (> n %forum-server-count)
            servers
            (loop (1+ n)
                  (cons (machine
                         (system (forum-server n))
                         (environment manged-host-environment-type)
                         (configuration (machine-ssh-configuration
                                         ...)))
                        servers)))))

The take-away from that example is that there's a new machine type atop the good ol' operating-system type, specifying how the machine should be provisioned. The version of guix deploy that's currently on the master branch only supports managed-host-environment-type, which is used for machines that are already up and running the Guix System. Provisioning, in that sense, only really involves opening an SSH connection to the host. But I'm sure you can imagine a linode-environment-type which automatically sets up a virtual private server through Linode, or a libvirt-environment-type that spins up a virtual machine for running your services. Those types are what I'll be working on in the coming months, in addition to cleaning up the code that's there now.

And yes, you did read that right. guix deploy is on the Guix master branch right now! In fact, we've already done a successful deployment right here on ci.guix.gnu.org. So, if this sounds as though it'd be up your alley, run guix pull, crack open the manual, and let us know how it goes!

About GNU Guix

GNU Guix is a transactional package manager and an advanced distribution of the GNU system that respects user freedom. Guix can be used on top of any system running the kernel Linux, or it can be used as a standalone operating system distribution for i686, x86_64, ARMv7, and AArch64 machines.

In addition to standard package management features, Guix supports transactional upgrades and roll-backs, unprivileged package management, per-user profiles, and garbage collection. When used as a standalone GNU/Linux distribution, Guix offers a declarative, stateless approach to operating system configuration management. Guix is highly customizable and hackable through Guile programming interfaces and extensions to the Scheme language.