How to deal with code duplication in puppet modules?

问题

I have implemented two puppet modules to setup and configure two components - A & B. The directory structure of the modules folder looks like below:

modules
     modulea
          manifests
               init.pp
               install.pp
               config.pp
               service.pp
          templates
               1.properties.erb (This one is also needed by moduleb)
               2.properties.erb (This one is also needed by moduleb)
     moduleb
          manifests          
               init.pp
               install.pp
               config.pp
               service.pp 
          templates
               1.properties.erb (same as in modulea)
               2.properties.erb (same as in modulea) 
               3.properties.erb
               4.properties.erb
               5.properties.erb

The code in install.pp and service.pp is identical in both the modules. The code in config.pp of modulea deals with 2 property files, while code in config.pp of moduleb deals with 5 property files. Out of these 5 property files, 2 property files are exactly same as modulea, while 3 property files are specific to moduleb.

Pasted below is install.pp and service.pp code:

**init.pp of modulea**
class modulea::install inherits modulea {
  package { $package_name: ensure => present }
}

**init.pp of moduleb**
class moduleb::install inherits moduleb {
  package { $package_name: ensure => present }
}

**service.pp of modulea**
class modulea::service inherits modulea {
  service { $service_name: ensure => running, }
}

**service.pp of moduleb**
class moduleb::service inherits moduleb {
  service { $service_name: ensure => running, }
}

What options do I have to reduce code duplication and improve the maintainability of code? What options do I have so that I can easily add one more module in future that has same pattern?

回答1:

To avoid puppet code duplication, I usually create "common class". I also recommend using hiera to parametrize common class. More about hiera: https://docs.puppetlabs.com/hiera/1/

As an example: class common::installer:

modules
    common
        installer.pp

with code:

class common::installer {
   $packages = hiera("common::installer::packages")
   package { $packages:
     ensure => latest,
   }
}

Next in all modules add

require common::installer #or include common::installer, with this you will avoid "already defined" errors in puppet.

In hiera, depend on machine configuration you define proper value of common::installer::packages

e.g in machineA.yaml

 common::installer::packages:
   - packageA
   - packageB
   - packageC

in machineB.yaml

 common::installer::packages:
   - packageA
   - packageB
   - packageD
   - packageE

This also gives you opportunity to install both modules A and B on one machine without any conflicts.

Just in hiera create proper config machineAandB.yaml with

 common::installer::packages:
   - packageA
   - packageB
   - packageC
   - packageD
   - packageE

You can also consider using ensure_package, to avoid annoying puppet errors with duplicated definition of packages, but with the code above i will not happen.

Similar code you can use to ensure that required services are running.

来源：https://stackoverflow.com/questions/27707014/how-to-deal-with-code-duplication-in-puppet-modules

标签

puppet

reusability

maintainability