Iñigo Aldazabal Mensa (CSIC-UPV: EHU ) - Harnessing your cluster with Ansible + hands on

The way to manage the configuration of computing nodes in HPC clusters is normally through, first, the use of some kind of master image deployed to the nodes and, second, a "post configuration" stage in which the installed system is modified in order to adapt it to the changes made to this base image: modified SLURM configuration files, new filesystems to be mounted, updated packages, new monitoring tools to be installed, etc.

One way to deal with this post-configuration stage, and also with further changes which happen along the life of a computing node, is using a Configuration Management System - CMS. CMS's, such as CFEngine, Puppet, Chef, Salt, etc., are specifically designed to deal with system configuration changes and to mantain consistency in complex systems: they allow us to define nodes' service states, configuration files, packages installed, mount points, security policies and much more.

But this also comes with a price: a steep learning curve and the CMS system setup itself. Here we will present Ansible, a very easy to use CMS which, with its clientless (zero initial setup in the nodes) push model and the simple, human readable syntax of its YAML configuration files, perfectly fits the mindset of HPC cluster administrators.

After the previous Ansible introductory talk we will walk through setting up a basic configuration for a simple computing cluster created with virtual machines. As an introductory step we will briefly present Vagrant, a tool which will allow us to create reproducible and portable virtual machine development and testing environments.

Using a very simple Vagrant configuration file we will setup a test cluster with a head node and a few computing nodes. Within the head node we will download Ansible, build a rpm package and install it. We will then write the inventory file with nodes of different types, make some test runs and create a basic Ansible playbook for eg. install some packages, distribute some configuration files and configure some services both in the head and the computing nodes.

The Vagrant configuration file and virtual machine template (Vagrant "box") as well as the base Ansible files we will use will be provided beforehand so that anyone interested will be able to follow along the session in his/her laptop. Check https://github.com/iamc/HPCKP15-Ansible-hands-on for more information.

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