Pre-Compiling Plugins

This guide will walk you through an example on how to pre-compile Sensu Plugins for distribution among clients. The goal of this guide is to showcase how you can quickly install plugins on ephemeral instances where time to compile can affect time to production. We’ll be using sensu-plugins-aws as it requires nokogiri, usually requiring a longer build time.

Prerequisites

Sources:

This guide assumes the following:

  • Centos 7 platform
  • You have some way to store these artifacts and make them available for systems in your environment

NOTE: Compiled gems are tied to the Ruby version they are compiled for. If Sensu upgrades Ruby 2.4 -> Ruby 2.5, packages will need to be rebuilt. NOTE: Compiled gems are tied to CPU architecture for which they are compiled on.

Installing the build toolchain

First we’ll add the Sensu yum repository definition and install Sensu.

IMPORTANT: Sensu Core reached end-of-life (EOL) on December 31, 2019, and we permanently removed the Sensu EOL repository on February 1, 2021. This means the baseurl specified in the code example below is no longer available. To migrate to Sensu Go, read the Sensu Core migration guide.

printf '[sensu]
name=sensu
baseurl=https://eol-repositories.sensuapp.org/yum/$releasever/$basearch/
gpgcheck=0
enabled=1' | sudo tee /etc/yum.repos.d/sensu.repo && sudo yum install -y sensu

Then install EPEL, dev tools, and libs required for the next steps.

sudo yum install -y epel-release
sudo yum groupinstall -y "Development Tools"
# installing dependencies for nokogiri
sudo yum install -y libxml2 libxslt libxslt-devel libxml2-devel gcc ruby-devel zlib-devel

Installing a gem to a tmp directory

Install the gem-compiler package:

sudo /opt/sensu/embedded/bin/gem install gem-compiler

We’ll now install the source gems into a cache directory.

mkdir /tmp/gems
sudo /opt/sensu/embedded/bin/gem install --no-document --install-dir /tmp/gems sensu-plugins-aws --version '=12.3.0'
sudo /opt/sensu/embedded/bin/gem install --no-document --install-dir /tmp/gems mini_portile2 --version '=2.3.0'

Observing the gem install output, we can see that nokogiri and unf_ext both build native extensions. These are the gems we will compile so we can install them from our own repository.

Compile the gems for packaging

We’ll use gem-compiler to rebuild the gem packages with the included native extensions:

cd /tmp/gems/cache
sudo /opt/sensu/embedded/bin/gem compile unf_ext-0.0.7.5.gem
sudo /opt/sensu/embedded/bin/gem compile nokogiri-1.8.5.gem --prune -- --use-system-libraries

NOTE: nokogiri requires –prune flag per gem-compiler readme notes NOTE: For nokogiri we also use -- --use-system-libraries so gem compile uses the system gcc and lib’s installed earlier

The resulting compiled gem files have a x86_64-linux in their file name denoting their system architecture:

# ls  -1 *-x86_64-linux.gem
nokogiri-1.8.5-x86_64-linux.gem
unf_ext-0.0.7.5-x86_64-linux.gem

Install Pre-Compiled Gems on Targeted System and Testing

Install compiled gem into embedded Ruby

Now we can copy these gems to another system and install them into the Sensu embedded ruby. In a production or development environment, you’d want to put these in a rubygems server of your own (e.g. [Geminabox(https://github.com/geminabox/geminabox), Artifactory or similar). You can also use a tool like fpm to convert the gems into a system package.

Here we’ve copied the compiled gems to a system with Sensu installed, but no gcc or other compile toolchain.

NOTE: nokogiri needs libxml2 and libxslt to be present on your system.

sudo /opt/sensu/embedded/bin/gem install unf_ext-0.0.7.5-x86_64-linux.gem
sudo /opt/sensu/embedded/bin/gem install nokogiri-1.8.5-x86_64-linux.gem

Install pre-complied Sensu plugins

With these prerequisites in place we can install sensu-plugins-aws without a compiler. You can use sensu-install or gem commands:

sudo /opt/sensu/embedded/bin/gem -p aws
[SENSU-INSTALL] installing Sensu plugins ...
[SENSU-INSTALL] determining if Sensu gem 'sensu-plugins-aws' is already installed ...
false
[SENSU-INSTALL] Sensu plugin gems to be installed: ["sensu-plugins-aws"]
[SENSU-INSTALL] installing Sensu gem 'sensu-plugins-aws'
Fetching: unf-0.1.4.gem (100%)
Successfully installed unf-0.1.4
Fetching: domain_name-0.5.20170404.gem (100%)
Successfully installed domain_name-0.5.20170404
Fetching: http-cookie-1.0.3.gem (100%)
Successfully installed http-cookie-1.0.3
Fetching: mime-types-2.99.3.gem (100%)
Successfully installed mime-types-2.99.3
Fetching: netrc-0.11.0.gem (100%)
Successfully installed netrc-0.11.0
Fetching: rest-client-1.8.0.gem (100%)
Successfully installed rest-client-1.8.0
Fetching: sensu-plugins-aws-10.0.3.gem (100%)
You can use the embedded Ruby by setting EMBEDDED_RUBY=true in /etc/default/sensu
Successfully installed sensu-plugins-aws-10.0.3
7 gems installed
[SENSU-INSTALL] successfully installed Sensu plugins: ["sensu-plugins-aws"]

To test our pre-compiled gems we can use check-elb-health-fog.rb as it should exercise the nokogiri dependency: NOTE: This is to demonstrate that there are no errors while executing the plugin.

sudo export AWS_ACCESS_KEY=fatchance
sudo export AWS_SECRET_KEY=noway
sudo /opt/sensu/embedded/bin/check-elb-health-fog.rb -n foo -r us-east-1
ELBHealth WARNING: An issue occurred while communicating with the AWS EC2 API:
There is no ACTIVE Load Balancer named 'foo'

Recap

In this guide we covered the components involved in building out Sensu pre-compiled plugins. This allows system builders a method to pre-compile gems for systems that you may not want all the build tools required installed on them or for an easy to ship package for deploying gems on systems that may not have access to the internet.