Persist updated disk CID before reattaching to ensure correct disk is used in attach_disk

Author: neddp

src/bosh-director/lib/bosh/director/disk_manager.rb

@@ -338,9 +338,11 @@ def update_disk_cpi(instance_plan, new_disk, old_disk)
         updates[:disk_cid] = new_disk_cid
       end
 
-      attach_disk(old_disk_model, instance_plan.tags)
-
+      # Persist the updated CID (and size/cloud_properties) BEFORE reattaching.
+      # The CPI may have replaced the disk (e.g. GCP snapshot-based type change),
+      # so attach_disk must read the new CID from the model, not the stale one.
       old_disk_model.update(updates)
+      attach_disk(old_disk_model, instance_plan.tags)
       @logger.info("Finished IaaS native update of disk '#{old_disk_model.disk_cid}'")
     end
 

src/bosh-director/spec/unit/bosh/director/disk_manager_spec.rb

@@ -289,6 +289,14 @@ module Bosh::Director
             model = Models::PersistentDisk.where(instance_id: instance_model.id, active: true).first
             expect(model.disk_cid).to eq('new-disk-cid-from-cpi')
           end
+
+          it 'persists the new CID before reattaching so attach uses the correct disk' do
+            allow(cloud).to receive(:update_disk).and_return('new-disk-cid-from-cpi')
+
+            disk_manager.update_persistent_disk(instance_plan)
+
+            expect(cloud).to have_received(:attach_disk).with('vm234', 'new-disk-cid-from-cpi')
+          end
         end
 
         context 'when CPI returns the same disk CID' do