Use Host#uid_ems to link host records to ems_events

If we are unable to find the host by ems_ref attempt to use the
host_uid_ems attribute

app/models/ems_event.rb

@@ -90,7 +90,17 @@ def self.process_vm_in_event!(event, options = {})
   end
 
   def self.process_host_in_event!(event, options = {})
+    uid_ems = event.delete(:host_uid_ems)
     process_object_in_event!(Host, event, options)
+
+    if event[:host_id].nil? && uid_ems.present?
+      # Attempt to find a host in the current EMS first, then fallback to archived hosts
+      host = Host.find_by(:ems_id => event[:ems_id], :uid_ems => uid_ems) || Host.find_by(:ems_id => nil, :uid_ems => uid_ems)
+      unless host.nil?
+        event[:host_id]     = host.id
+        event[:host_name] ||= host.name
+      end
+    end
   end
 
   def self.process_container_entities_in_event!(event, _options = {})

spec/models/ems_event_spec.rb

@@ -275,6 +275,34 @@
         end
       end
     end
+
+    context "with a host" do
+      let(:event) do
+        {
+          :ems_id       => ems.id,
+          :event_type   => "HostAddEvent",
+          :host_uid_ems => host.uid_ems
+        }
+      end
+
+      context "with an active host" do
+        let(:host) { FactoryBot.create(:host, :uid_ems => "6f3fa3f1-bbe0-4aab-9a69-5d652324357f", :ext_management_system => ems) }
+
+        it "should link the event to the host" do
+          ems_event = described_class.add(ems.id, event)
+          expect(ems_event.host).to eq(host)
+        end
+      end
+
+      context "with an archived host" do
+        let(:host) { FactoryBot.create(:host, :uid_ems => "6f3fa3f1-bbe0-4aab-9a69-5d652324357f") }
+
+        it "should link the event to the host" do
+          ems_event = described_class.add(ems.id, event)
+          expect(ems_event.host).to eq(host)
+        end
+      end
+    end
   end
 
   context '.event_groups' do