Volcane recently asked in ##infra-talk on Freenode if anyone knew of "some little tool that can be used in a cronjob for example to noop the the real task if say load avg is high or similar?"

I came up with the idea to use nagios plugins. So, for example, to check load average before running a task:

/usr/lib64/nagios/plugins/check_load -w 0.7,0.6,0.5 -c 0.9,0.8,0.7 >/dev/null && echo "Run the task here"

Substitute the values used for the -w and -c args as appropriate, or use a different plugin for different conditions.

In a previous post, I described how to describe puppet environments, roles, and profiles, as modules and how to use r10k and librarian-puppet to deploy them.

One possible problem with deploying to the puppet environment directory directly is that the librarian-puppet run can take some time and there is a possibility that puppet may attempt to compile a catalogue in an incomplete or inconsistent environment. One way to overcome this is to deploy the environments into a new directory, create a symlink, and move the symlink atomically into place.

This would look something like this:

cd /etc/puppet/envs
# create a new dir under /etc/puppet/envs - I use a timestamp in the name so I know when it was created
NEW_ENV_DIR=$(mktemp --directory envs.$(date -Isec).XXX")
cd /etc/puppet
# use r10k deploy the environments into the new dir
PUPPETFILE_DIR="envs/${NEW_ENV_DIR}" r10k puppetfile install
# loop over all the environments and use librarian-puppet to deploy all the roles/profiles/modules
while read env ; do
  pushd $env
  LIBRARIAN_PUPPET_PATH=modules librarian-puppet install --no-use-v1-api --strip-dot-git
done < <(find "/etc/puppet/envs/${NEW_ENV_DIR}" -maxdepth 1 -mindepth 1 -type d)
ln -s /etc/puppet/envs/${NEW_ENV_DIR} /etc/puppet/envs/environments
mv /etc/puppet/envs/environments /etc/puppet

I have written a script that does all of this in a more robust way and also uses parallel to speed up the deployment process.

The script and the role and profile modules references in my previous article are in this github repo.

By treating roles and profiles as puppet modules, we can use r10k and librarian-puppet to manage the deployment of our puppet code into our puppet environements.

I shall assume that puppet is configured to use to use directory environments and that the environment path is $confdir/environments (ie. the default location). I also assume that both r10k and librarian-puppet are installed and in the path.

You should also understand and embrace the role-profile-module pattern, first described by Craig Dunn and subsequently by Adrian Thebo and Gary Larizza. Quoting Gary:

  • Roles abstract profiles
  • Profiles abstract component modules
  • Hiera abstracts configuration data
  • Component modules abstract resources
  • Resources abstract the underlying OS implementation 

I find the following points useful to clarify the purpose of each of the layers in this model:

  • Roles, profiles, and component modules can all be implemented as puppet modules
  • Each node is assigned exactly one role (either in site.pp or, preferably, using some external node classifier)
  • Each role includes one or more profiles
  • Each profile loads configuration data and feeds it into the component modules – this is where your business logic should go
  • Each component module should be generic and contain no site-specific data. You should be able to publish all your component modules on PuppetForge without leaking any secrets.

We can further extend this model to include environments. An environment can be thought of as a group of roles and can also be implemented as a puppet module.

So, how do we set this up?

At the top-level, we put a Puppetfile in the puppet config dir containing a list of our environments. This will look something like this:

#!/usr/bin/env ruby
#^syntax detection

forge 'https://forgeapi.puppetlabs.com'

mod 'yo61-env_production',
  :git => 'git@github.com:yo61/puppet-demo_env_production.git'

mod 'yo61-env_staging',
  :git => 'git@github.com:yo61/puppet-demo_env_staging.git'

Each environment is defined as a puppet module. Any valid Puppetfile syntax may be used to specifiy the module location, including alternate branches or specific version tags. 

Each of the environment modules should contain all the usual things you would put in a puppet environment, eg. a manifests/site.pp, etc. as well as a Puppetfile containing a list of all the roles to be deployed to this environment. The Puppetfile for a simple environment would look something like this:

#!/usr/bin/env ruby
#^syntax detection

forge "https://forgeapi.puppetlabs.com"

# list all the roles that are included in this environment
mod 'yo61-role_default',
  :git => 'git@github.com:yo61/puppet-demo-roles-profiles.git',
  :path => 'modules/role_default'

mod 'yo61-role_foo',
  :git => 'git@github.com:yo61/puppet-demo-roles-profiles.git',
  :path => 'modules/role_foo'

mod 'yo61-role_bar',
  :git => 'git@github.com:yo61/puppet-demo-roles-profiles.git',
  :path => 'modules/role_bar'

Like the top-level Puppetfile used to defined environments, each role is defined as a puppet module.

Each of the role modules will contain a simple class that loads the profiles used by the role, and a Puppetfile containing a list of all profiles used by the role. The Puppetfile for a simple role would look something like this:

#!/usr/bin/env ruby
#^syntax detection

forge "https://forgeapi.puppetlabs.com"

# list all the profiles that are included in this role
mod 'yo61-profile_common',
  :git => 'git@github.com:yo61/puppet-demo-roles-profiles.git',
  :path => 'modules/profile_common'

Each of the profile modules will contain all the puppet code required to define the business logic, load configuration data, etc. and a Puppetfile containing a list of all the component modules used by the profile. The Puppetfile for a simple profile would look something like this:

#!/usr/bin/env ruby
#^syntax detection

forge "https://forgeapi.puppetlabs.com"

# include all the modules used by this profile
mod 'puppetlabs-stdlib',
mod 'stahnma-epel'
mod 'puppetlabs-ntp'

Again, any valid Puppetfile syntax may be used.

We've now defined all our environments, roles, and profiles and we're ready to deploy each environment.

First, we run r10k to deploy each of the environment modules into the environment dir (/etc/puppet/environments):

# switch to the location of the top-level Puppetfile
cd /etc/puppet
PUPPETFILE_DIR=/etc/puppet/environments r10k puppetfile install

This will create a directory in /etc/puppet/environments for each of the environments defined in the top-level Puppetfile.

Next, we change into each of the newly-created environment directories and run librarian-puppet to install all the roles required by that environment.

cd /etc/puppet/environments/production
LIBRARIAN_PUPPET_PATH=modules librarian-puppet install --no-use-v1-api --strip-dot-git

The best bit is that librarian-puppet supports recursive module dependency resolution so this one command installs not only the roles, but also all the profiles, and component modules required by each of the roles.

My next article will present a script that runs r10k and librarian-puppet as described in this article, and also updates puppet environments atomically