Fall back to interface bindings when the primary IP matches no subnet

modules/libs/lib/facter/subnet_facts.rb

@@ -28,21 +28,37 @@ class SubnetAttributes
   # Default attributes if no subnet matches, also defined as a constant
   DEFAULT_ATTRIBUTES = { environment: 'unknown', region: 'unknown', country: 'unknown' }.freeze
 
-  # provide ip to return attributes
+  # loopbacks and wg /31s sit in syd1 ranges, so they must not decide where a host lives
-  def self.attributes(ip)
+  SKIPPED_INTERFACES = /\A(lo\z|dum|wg)/.freeze
-    SUBNET_TO_ATTRIBUTES.each do |subnet, attrs|
-      return attrs if IPAddr.new(subnet).include?(IPAddr.new(ip))
-    end
 
-    DEFAULT_ATTRIBUTES
+  # primary ip first, then the remaining interfaces in name order
+  def self.from_networking(networking)
+    match(networking['ip']) || interface_match(networking['interfaces'] || {}) || DEFAULT_ATTRIBUTES
+  end
+
+  def self.interface_match(interfaces)
+    interfaces.sort
+              .reject { |name, _interface| name.match?(SKIPPED_INTERFACES) }
+              .flat_map { |_name, interface| addresses(interface) }
+              .lazy.filter_map { |address| match(address) }.first
+  end
+
+  def self.addresses(interface)
+    (interface['bindings'] || []).map { |binding| binding['address'] }
+  end
+
+  def self.match(ip)
+    return unless ip
+
+    addr = IPAddr.new(ip)
+    SUBNET_TO_ATTRIBUTES.each do |subnet, attrs|
+      return attrs if IPAddr.new(subnet).include?(addr)
+    end
+    nil
   end
 end
 
-# Use the primary IP address from facts
+subnet_attributes = SubnetAttributes.from_networking(Facter.value(:networking))
-ip = Facter.value(:networking)['ip']
-
-# Call the class method directly without creating an instance
-subnet_attributes = SubnetAttributes.attributes(ip)
 
 # Add separate facts for environment, region, and country
 Facter.add('environment') { setcode { subnet_attributes[:environment] } }

modules/libs/test/subnet_facts_check.rb

@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+# ruby modules/libs/test/subnet_facts_check.rb
+module Facter
+  def self.value(_name)
+    {}
+  end
+
+  def self.add(*); end
+end
+load File.expand_path('../lib/facter/subnet_facts.rb', __dir__)
+
+iface = ->(*addresses) { { 'bindings' => addresses.map { |address| { 'address' => address } } } }
+
+checks = {
+  'primary ip wins over other interfaces' => [
+    { 'ip' => '198.18.17.5', 'interfaces' => { 'eth1' => iface.call('198.18.13.5') } }, 'drw1'
+  ],
+  'unmatched primary ip falls back to an interface' => [
+    { 'ip' => '203.0.113.5', 'interfaces' => { 'eth0' => iface.call('203.0.113.5'), 'eth1' => iface.call('198.18.24.11') } }, 'syd1'
+  ],
+  'lo, dum and wg interfaces are skipped' => [
+    { 'ip' => '203.0.113.5',
+      'interfaces' => { 'dum0' => iface.call('198.18.2.161'), 'lo' => iface.call('198.18.19.1'),
+                        'wg0' => iface.call('198.18.2.177') } }, 'unknown'
+  ],
+  'interfaces are scanned in name order' => [
+    { 'ip' => '203.0.113.5', 'interfaces' => { 'eth2' => iface.call('198.18.24.1'), 'eth1' => iface.call('198.18.17.1') } }, 'drw1'
+  ],
+  'missing ip and interfaces resolve to unknown' => [{}, 'unknown']
+}
+
+failures = checks.reject { |_name, (networking, expected)| SubnetAttributes.from_networking(networking)[:region] == expected }
+failures.each_key { |name| warn "FAIL: #{name}" }
+abort if failures.any?
+puts "ok (#{checks.size} checks)"