| Purpose |
Standard library for creating Puppet modules |
| Module |
puppetlabs/stdlib |
| Puppet Version |
2.6+ |
| Platforms |
Redhat, Debian, Solaris, Mac OS X, Windows |
Welcome back to the module of the week! Previously we
covered facter-dot-d. This week we're switching our focus to the
puppetlabs/stdlib data functions:
getvar,
loadyaml, and
merge.
The data functions provide the ability to dynamically lookup data from Puppet namespaces, load data from external YAML files, and merge Hashes. These powerful features make it easy to separate Puppet code from data without the complexity of using an
External Node Classifier or
Custom Facts; leaving your manifests more readable and maintainable as a result.
Example Usage
In this brief tutorial I'm going to cover the
loadyaml and
merge functions to show you just how easy it is to work with external data:
The loadyaml function
As its name implies the
loadyaml function allows us to load data from an external YAML file.
/etc/puppet/data/webservers/data.yaml
ports:
http: 80
https: 443
tomcat: 8080
webdir: /var/www/html
/etc/puppet/modules/webservers/manifests/init.pp
class webservers {
include 'stdlib'
$data = loadyaml('/etc/puppet/data/webservers/data.yaml')
$http_port = $data[ports][http] # => 80
$https_port = $data[ports][https] # => 443
$webdir = $data[webdir] # => '/var/www/html'
...
}
Lets step through this:
- First we create a data file
/etc/puppet/data/webservers/data.yaml
- Then we make a call to
loadyaml with the full path to our data file
- Next
loadyaml processes data.yaml and returns a Hash, which is then assigned to $data
- Finally we set the
$http, $https, and $webdir variables by referencing the $data Hash
The merge function
The
merge function allows us to merge two or more Hashes:
/etc/puppet/data/webservers/data.yaml
ports:
http: 80
https: 443
tomcat: 8080
webdir: /var/www/html
/etc/puppet/data/database/data.yaml
ports:
db: 5432
/etc/puppet/modules/webservers/manifests/init.pp
class webservers {
include 'stdlib'
$myhash = { database_user => 'webdata', webdir => '/var/html' }
$webserver_data = loadyaml('/etc/puppet/data/webservers/data.yaml')
$database_data = loadyaml('/etc/puppet/data/database/data.yaml')
$data = merge($myhash, $webserver_data, $database_data)
$http_port = $data[ports][http] # => 80
$https_port = $data[ports][https] # => 443
$webdir = $data[webdir] # => '/var/www/html'
$db_port = $data[ports][db] # => 5432
...
}
Here we are calling the
merge function with three Hashes (
$myhash,
$webserver_data, and
$database_data) which yields a single
$data Hash.
Note, the
merge function overrides duplicate keys with the argument farthest to the right "winning". In the above example the
webdir value provided by
$myhash is overridden by the value provided by
$webserver_data.
Conclusion
The data functions provided by
puppetlabs/stdlib makes it easy to work with internal and external data. While great for simple use-cases, this mode of operation doesn't scale. Once the number of external data files or Puppet modules grows, you'll find your modules littered with lots of
getvar,
loadyaml, and
merge function calls.
A better solution for more complex requirements is
Hiera. While providing all the features of
getvar,
loadyaml, and
merge, Hiera includes the ability to load data from virtually anywhere. Via Hiera's pluggable backend interface, you'll be able to pull data from external databases such as
Redis, or
JSON files; the possibilities are endless.
That wraps up our coverage of the
puppetlabs/stdlib module. Hopefully you can now leverage some of its features in your own modules and have a sense of how robust Puppet modules can be.
Additional Resources
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