Checking if a directory exists before copying in Puppet - puppet

Question

I am trying to get a backup of a subdirectory before deleting the parent directory by copying the subdirectory into a different location.
This is how I have done this:
exec { "install_path_exists":
command => "/bin/true",
onlyif => "/usr/bin/test -d ${install_path}",
path => ['/usr/bin','/usr/sbin','/bin','/sbin'],
}
file { "server_backup_dir" :
ensure => 'directory',
path => "${distribution_path}/backup/server",
recurse => true,
source => "file:///${install_path}/repository/deployment/server",
require => Exec["install_path_exists"],
}
Exec checks if the directory exists, and returns true if so. The "server_backup_dir" file resource requires the "install_path_exists" exec to return true if the directory exists.
When the directory does not exist, and "install_path_exists" returns false, "server_backup_dir" executes anyway, and produces the following error.
Error: /Stage[main]/Is/File[server_backup_dir]: Could not evaluate:
Could not retrieve information from environment production source(s)
file:////usr/local/{project_location}/repository/deployment/server
What is wrong with my approach, and how can I fix this? Thanks in advance.

Answer 1

I'll break this up into two parts, what is wrong, and how to fix it.
What is wrong with my approach ...
You are misunderstanding the 'require' line and the nature of relationships in Puppet, and also how Puppet uses the return code of the command executed in an Exec.
When you use any of the four so-called metaparameters for relationships in Puppet - those being: require, before, subscribe & notify - you tell Puppet that you want the application of one resource to be ordered in time in relation to another. (Additionally, the 'subscribe' and 'notify' respond to refresh events but that's not relevant here.)
So, when Puppet applies a catalog built from your code, it will firstly apply the Exec resource, i.e. execute the /bin/true command, if and only if the install path exists; and then it will secondly manage the server_backup_dir File resource. Note also that it will apply the File resource irrespective of whether the Exec command actually was executed; the only guarantee being that /bin/true will never be run after the File resource.
Furthermore, the return code of the command in the Exec functions differently to what you're expecting. An exit status of 0 as the /bin/true command returns only tells Puppet to allow configuration to continue; compare that to an Exec command returning a non-zero exit status, which would cause Puppet to halt execution with an error.
Here's a simple demonstration of that:
▶ puppet apply -e "exec { '/usr/bin/false': }"
Notice: Compiled catalog for alexs-macbook-pro.local in environment production in 0.08 seconds
Error: '/usr/bin/false' returned 1 instead of one of [0]
Error: /Stage[main]/Main/Exec[/usr/bin/false]/returns: change from 'notrun' to ['0'] failed: '/usr/bin/false' returned 1 instead of one of [0]
Notice: Applied catalog in 0.02 seconds
For more info, read the page I linked above carefully. It generally takes a bit of time to get your head around relationships and ordering in Puppet.
how can I fix this?
You would normally use a custom fact like this:
# install_path.rb
Facter.add('install_path') do
setcode do
Facter::Core::Execution.execute('/usr/bin/test -d /my/install/path')
end
end
And then in your manifests:
if $facts['install_path'] {
file { "server_backup_dir" :
ensure => 'directory',
path => "${distribution_path}/backup/server",
recurse => true,
source => "file:///my/install/path/repository/deployment/server",
}
}
Consults docs for more info on writing and including custom facts in your code base.
Note:
I notice at the end that you reuse $install_path in the source parameter. If your requirement is to have a map of install paths to distribution paths, you can also build a structured fact. Without knowing exactly what you're trying to do, however, I can't be sure how you would write that piece.