https://community.theforeman.org/t/custom-ipam-provider-solarwinds/8859

engine.rb

# lib/foreman_solarwinds/engine.rb
   config.autoload_paths += Dir["#{config.root}/app/services"]
   config.autoload_paths += Dir["#{config.root}/app/services/concerns"]

   config.to_prepare do
      begin
        ::IPAM.send(:include, ForemanSolarwinds::IpamExtensions)
      rescue StandardError => e
        Rails.logger.warn "ForemanSolarwinds: skipping engine hook (#{e})"
      end
    end

ipam_extensions.rb

# app/services/concerns/foreman_solarwinds/ipam_extensions.rb
module ForemanSolarwinds
  module IpamExtensions
    extend ActiveSupport::Concern

    module Overrides
      module ClassMethods
        def new(type, *args)
          if type == ::IPAM::MODES[:solarwinds]
            ::IPAM::Solarwinds.new(*args)
          else
            super
          end
        end
      end

      def self.prepended(base)
        class << base
          prepend ClassMethods
        end
      end
    end

    included do
      ::IPAM::MODES[:solarwinds] ||= N_('Solarwinds')

      prepend Overrides
    end
  end
end

solarwinds.rb

# app/services/ipam/solarwinds.rb
module IPAM
  class Solarwinds < Base
    def suggest_ip
      # Your code here
    end
  end
end