In Puppet, how to use defined node variables in an if clause - variables

Question

In a puppet class how should I test if a variable has been set in a node?
I use a VM name (like server1) and a domain name (like example.org) where users can reach the page. "example.org" won't be conveyed via a fact, so I need to pass it via a class parameter. I came up with this way to define the variable in a node block and use it in my test class for my settings.
node "VM1" {
class { 'test':
domainname => "example.org",
}
[...]
class test ($domainname) {
ini_setting {
'set_property':
ensure => present,
path => '/tmp/test.ini',
section => 'main',
setting => 'url',
value => "https://$domainname";
}
[...]
But now I want to add a condition that if $domainname isn't set then the $hostname fact should be used in its place.
ini_setting {
'set_property':
ensure => present,
path => '/tmp/test.ini',
section => 'main',
setting => 'url',
if $domainname !~ $hostname {
value => "https://$domainname";
} else {
value => "https://$hostname";
}
But now I get an error like this every time:
Error: Could not retrieve catalog from remote server: Error 500 on SERVER: Server Error: Syntax error at 'domainname'
What should I do instead?

Answer 1

The error message is explaining to you that if statements cannot appear inside resource declarations. There is, however, a different conditional form, called a "selector" that can appear inside resource declarations. It is Puppet's analog of the ternary ?: operator that appears in several languages.
Stylistically, though, it is usually better form to keep resource declarations as simple as possible. To that end, you should probably set a variable, conditionally, outside the resource declaration, and then use its value inside. Using your own conditional, that might look like this:
if $domainname !~ $hostname {
$url_value = "https://$domainname";
} else {
$url_value = "https://$hostname";
}
ini_setting {
'set_property':
ensure => present,
path => '/tmp/test.ini',
section => 'main',
setting => 'url',
value => $url_value;
}
Additionally, however, I note that your particular condition, repeated above, is highly suspect. In recent Puppet (version 4 and above), you should be using Puppet data types to both declare your class parameters and check them. In particular, if it is permissible to declare class test without providing a $domainname parameter, then you would declare that class like so:
# Using the Puppet v4+ type system
class test(
Optional[String] $domainname = undef
) {
# ...
, and would test whether a value was provided for $domainname like so:
if $domainname =~ Undef {
# ...
}
You cannot use the type system in earlier Puppet, but there you can rely on undefined variables to expand to nothing when you interpolate them:
# Using the Puppet v3- behavior
class test(
$domainname = undef
) {
# ...
if "$domainname" == "" {
# ...
}
# ...
}