Facter 3 and 4 behave inconsistently with respect to fact values that return nil vs empty strings summarized as below:
|Fact Type|Facter 3|Facter 4|
|custom legacy|omitted|omitted|
|custom structured|nil|nil|
|external legacy|""|omitted|
|external structured|omitted|nil|
{{custom}} means the fact is defined using the Ruby API {{Facter.add}}
{{external}} means the fact is defined as a JSON data file
{{legacy}} means the fact returns a single value
{{structured}} means the fact's value is a Hash
Puppet always converts nil fact values to "", see PUP-11446, so the "external legacy" case means puppet 7 may omit a fact that was previously included when requesting a catalog. For example:
{noformat}
# puppet apply -e 'notice($external_legacy == undef)'
Notice: Scope(Class[main]): false
...
# puppet apply --facterng -e 'notice($external_legacy == undef)'
Warning: Unknown variable: 'external_legacy'. (line: 1, column: 8)
Notice: Scope(Class[main]): true
...
{noformat}
If you're using {{strict_variables}} then catalog compilation will fail (since the fact is missing):
{noformat}
# puppet apply --strict_variables --facterng -e 'notice($external_legacy == undef)'
Error: Evaluation Error: Unknown variable: 'external_legacy'. (line: 1, column: 8) on node
{noformat}
The "external structured" case has the opposite problem. Previously the fact was omitted and now it will be present with an empty value (due to Puppet converting nil to ""):
{noformat}
# puppet apply -e 'notice($facts["external_structured"].keys)'
Notice: Scope(Class[main]): [boolean, integer]
...
# puppet apply --facterng -e 'notice($facts["external_structured"].keys)'
Notice: Scope(Class[main]): [null, integer, boolean]
...
# puppet apply --facterng -e 'notice($facts["external_structured"].values)'
Notice: Scope(Class[main]): [, 42, false]
...
# puppet apply --facterng -e 'notice($facts["external_structured"].values[0] =~ String)'
Notice: Scope(Class[main]): true
{noformat}
These might break puppet manifests that are not expecting to receive the "extra" key-value pair.
h3. Custom Legacy Facts
Facter 3 and 4 both omit legacy facts with nil values when collecting all facts {{ {} Facter.to_hash { }} } :
{noformat}
# cat custom/custom_legacy.rb
Facter.add(:custom_legacy) { setcode { nil } }
# /opt/puppetlabs/puppet/bin/facter -j --custom-dir /root/custom | grep custom_legacy
# /opt/puppetlabs/puppet/bin/facter-ng -j --custom-dir /root/custom | grep custom_legacy
#
{noformat}
One inconsistency is if you ask for the fact by name, Facter 3 returns a fact with an empty value, while Facter 4 returns nil:
{noformat}
# /opt/puppetlabs/puppet/bin/facter -j --custom-dir /root/custom custom_legacy
{
"custom_legacy": ""
}
# /opt/puppetlabs/puppet/bin/facter-ng -j --custom-dir /root/custom custom_legacy
{
"custom_legacy": null
}
{noformat}
h3. Custom Structured Facts
Facter 3 and 4 are consistent when a structured fact contains a fact whose value is nil (the fact is present with a nil value)
{noformat}
# cat custom/custom_structured.rb
Facter.add(:custom_structured) do
setcode do
{
"null" => nil,
"integer" => 42,
"boolean" => false
}
end
end
# /opt/puppetlabs/puppet/bin/facter -j --custom-dir /root/custom custom_structured
{
"custom_structured": {
"null": null,
"integer": 42,
"boolean": false
}
}
# /opt/puppetlabs/puppet/bin/facter-ng -j --custom-dir /root/custom custom_structured
{
"custom_structured": {
"boolean": false,
"integer": 42,
"null": null
}
}
{noformat}
h3. External Legacy Facts
Facter 3 returns an empty string, while Facter 4 omits the fact:
{noformat}
# cat external/external_legacy.txt
external_legacy=
# /opt/puppetlabs/puppet/bin/facter -j --external-dir /root/external | grep external_legacy
"external_legacy": "",
# /opt/puppetlabs/puppet/bin/facter-ng -j --external-dir /root/external | grep external_legacy
#
{noformat}
h3. External Structured Facts
Facter 3 omits structured facts whose values are nil, while Facter 4 returns the fact with a nil value:
{noformat}
# cat external/external_structured.json
{
"external_structured": {
"null": null,
"integer": 42,
"boolean": false
}
}
# /opt/puppetlabs/puppet/bin/facter -j --external-dir /root/external external_structured
{
"external_structured": {
"boolean": false,
"integer": 42
}
}
# /opt/puppetlabs/puppet/bin/facter-ng -j --external-dir /root/external external_structured
{
"external_structured": {
"boolean": false,
"integer": 42,
"null": null
}
}
{noformat}
h3. Summary
In the "external legacy" case, facter 3 returns a {{nil}} value which puppet converts to "", see PUP-11446, while facter 4 omits the fact. For example:
{noformat}
# puppet apply -e 'notice($external_legacy == undef)'
Notice: Scope(Class[main]): false
...
# puppet apply --facterng -e 'notice($external_legacy == undef)'
Warning: Unknown variable: 'external_legacy'. (line: 1, column: 8)
Notice: Scope(Class[main]): true
...
{noformat}
If you're using strict_variables then catalog compilation will fail (since the fact is missing):
{noformat}
# puppet apply --strict_variables --facterng -e 'notice($external_legacy == undef)'
Error: Evaluation Error: Unknown variable: 'external_legacy'. (line: 1, column: 8) on node
{noformat}
The "external structured" case has the opposite problem. Previously the fact was omitted and now it will be present with an empty value (due to Puppet converting nil to ""):
{noformat}
# puppet apply -e 'notice($facts["external_structured"].keys)'
Notice: Scope(Class[main]): [boolean, integer]
...
# puppet apply --facterng -e 'notice($facts["external_structured"].keys)'
Notice: Scope(Class[main]): [null, integer, boolean]
...
# puppet apply --facterng -e 'notice($facts["external_structured"].values)'
Notice: Scope(Class[main]): [, 42, false]
...
# puppet apply --facterng -e 'notice($facts["external_structured"].values[0] =~ String)'
Notice: Scope(Class[main]): true
{noformat}
These might break puppet manifests that are not expecting to receive the "extra" key-value pair. |
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