Merge pull request juju#18479 from ycliuhw/fix-model-export

juju#18479

This PR resolves an issue with duplicate model data export during model migration. The problem occurred because domain exporters were registered each time the `ExportModel` method was called. These exporters were cached in the coordinator on the apiserver context and reused for all model migration requests, leading to repeated data exports if the migrate command was run multiple times.

## Checklist

- [x] Code style: imports ordered, good names, simple structure, etc
- [x] Comments saying why design decisions were made
- [x] Go unit tests, with comments saying what you're testing
- [ ] ~[Integration tests](https://github.com/juju/juju/tree/main/tests), with comments saying what you're testing~
- [ ] ~[doc.go](https://discourse.charmhub.io/t/readme-in-packages/451) added or updated in changed packages~

## QA steps

Before: the one block device item has been exported 6 times.
```
 block-devices:
 version: 2
 block-devices:
 - name: nvme0n1p16
 links:
 - /dev/disk/by-diskseq/9-part16
 - /dev/disk/by-id/nvme-Amazon_Elastic_Block_Store_vol04a3dc4efb35169b7-part16
 - /dev/disk/by-id/nvme-Amazon_Elastic_Block_Store_vol04a3dc4efb35169b7_1-part16
 - /dev/disk/by-id/nvme-uuid.b9fa7db8-4243-56ed-80d0-f8cd79b8e8f7-part16
 - /dev/disk/by-label/BOOT
 - /dev/disk/by-partuuid/1b154230-375f-4a23-827a-0d7830f7c0c1
 - /dev/disk/by-path/pci-0000:00:04.0-nvme-1-part16
 - /dev/disk/by-uuid/d726071f-b770-48f2-8f6f-3016a0245f0f
 label: BOOT
 uuid: d726071f-b770-48f2-8f6f-3016a0245f0f
 serial-id: Amazon_Elastic_Block_Store_vol04a3dc4efb35169b7_1
 wwn: uuid.b9fa7db8-4243-56ed-80d0-f8cd79b8e8f7
 size: 913
 fs-type: ext4
 in-use: true
 mount-point: /boot
 - name: nvme0n1p16
 links:
 - /dev/disk/by-diskseq/9-part16
 - /dev/disk/by-id/nvme-Amazon_Elastic_Block_Store_vol04a3dc4efb35169b7-part16
 - /dev/disk/by-id/nvme-Amazon_Elastic_Block_Store_vol04a3dc4efb35169b7_1-part16
 - /dev/disk/by-id/nvme-uuid.b9fa7db8-4243-56ed-80d0-f8cd79b8e8f7-part16
 - /dev/disk/by-label/BOOT
 - /dev/disk/by-partuuid/1b154230-375f-4a23-827a-0d7830f7c0c1
 - /dev/disk/by-path/pci-0000:00:04.0-nvme-1-part16
 - /dev/disk/by-uuid/d726071f-b770-48f2-8f6f-3016a0245f0f
 label: BOOT
 uuid: d726071f-b770-48f2-8f6f-3016a0245f0f
 serial-id: Amazon_Elastic_Block_Store_vol04a3dc4efb35169b7_1
 wwn: uuid.b9fa7db8-4243-56ed-80d0-f8cd79b8e8f7
 size: 913
 fs-type: ext4
 in-use: true
 mount-point: /boot
 - name: nvme0n1p16
 links:
 - /dev/disk/by-diskseq/9-part16
 - /dev/disk/by-id/nvme-Amazon_Elastic_Block_Store_vol04a3dc4efb35169b7-part16
 - /dev/disk/by-id/nvme-Amazon_Elastic_Block_Store_vol04a3dc4efb35169b7_1-part16
 - /dev/disk/by-id/nvme-uuid.b9fa7db8-4243-56ed-80d0-f8cd79b8e8f7-part16
 - /dev/disk/by-label/BOOT
 - /dev/disk/by-partuuid/1b154230-375f-4a23-827a-0d7830f7c0c1
 - /dev/disk/by-path/pci-0000:00:04.0-nvme-1-part16
 - /dev/disk/by-uuid/d726071f-b770-48f2-8f6f-3016a0245f0f
 label: BOOT
 uuid: d726071f-b770-48f2-8f6f-3016a0245f0f
 serial-id: Amazon_Elastic_Block_Store_vol04a3dc4efb35169b7_1
 wwn: uuid.b9fa7db8-4243-56ed-80d0-f8cd79b8e8f7
 size: 913
 fs-type: ext4
 in-use: true
 mount-point: /boot
 - name: nvme0n1p16
 links:
 - /dev/disk/by-diskseq/9-part16
 - /dev/disk/by-id/nvme-Amazon_Elastic_Block_Store_vol04a3dc4efb35169b7-part16
 - /dev/disk/by-id/nvme-Amazon_Elastic_Block_Store_vol04a3dc4efb35169b7_1-part16
 - /dev/disk/by-id/nvme-uuid.b9fa7db8-4243-56ed-80d0-f8cd79b8e8f7-part16
 - /dev/disk/by-label/BOOT
 - /dev/disk/by-partuuid/1b154230-375f-4a23-827a-0d7830f7c0c1
 - /dev/disk/by-path/pci-0000:00:04.0-nvme-1-part16
 - /dev/disk/by-uuid/d726071f-b770-48f2-8f6f-3016a0245f0f
 label: BOOT
 uuid: d726071f-b770-48f2-8f6f-3016a0245f0f
 serial-id: Amazon_Elastic_Block_Store_vol04a3dc4efb35169b7_1
 wwn: uuid.b9fa7db8-4243-56ed-80d0-f8cd79b8e8f7
 size: 913
 fs-type: ext4
 in-use: true
 mount-point: /boot
 - name: nvme0n1p16
 links:
 - /dev/disk/by-diskseq/9-part16
 - /dev/disk/by-id/nvme-Amazon_Elastic_Block_Store_vol04a3dc4efb35169b7-part16
 - /dev/disk/by-id/nvme-Amazon_Elastic_Block_Store_vol04a3dc4efb35169b7_1-part16
 - /dev/disk/by-id/nvme-uuid.b9fa7db8-4243-56ed-80d0-f8cd79b8e8f7-part16
 - /dev/disk/by-label/BOOT
 - /dev/disk/by-partuuid/1b154230-375f-4a23-827a-0d7830f7c0c1
 - /dev/disk/by-path/pci-0000:00:04.0-nvme-1-part16
 - /dev/disk/by-uuid/d726071f-b770-48f2-8f6f-3016a0245f0f
 label: BOOT
 uuid: d726071f-b770-48f2-8f6f-3016a0245f0f
 serial-id: Amazon_Elastic_Block_Store_vol04a3dc4efb35169b7_1
 wwn: uuid.b9fa7db8-4243-56ed-80d0-f8cd79b8e8f7
 size: 913
 fs-type: ext4
 in-use: true
 mount-point: /boot
 - name: nvme0n1p16
 links:
 - /dev/disk/by-diskseq/9-part16
 - /dev/disk/by-id/nvme-Amazon_Elastic_Block_Store_vol04a3dc4efb35169b7-part16
 - /dev/disk/by-id/nvme-Amazon_Elastic_Block_Store_vol04a3dc4efb35169b7_1-part16
 - /dev/disk/by-id/nvme-uuid.b9fa7db8-4243-56ed-80d0-f8cd79b8e8f7-part16
 - /dev/disk/by-label/BOOT
 - /dev/disk/by-partuuid/1b154230-375f-4a23-827a-0d7830f7c0c1
 - /dev/disk/by-path/pci-0000:00:04.0-nvme-1-part16
 - /dev/disk/by-uuid/d726071f-b770-48f2-8f6f-3016a0245f0f
 label: BOOT
 uuid: d726071f-b770-48f2-8f6f-3016a0245f0f
 serial-id: Amazon_Elastic_Block_Store_vol04a3dc4efb35169b7_1
 wwn: uuid.b9fa7db8-4243-56ed-80d0-f8cd79b8e8f7
 size: 913
 fs-type: ext4
 in-use: true
 mount-point: /boot
```

After:
```
 block-devices:
 version: 2
 block-devices:
 - name: nvme0n1p16
 links:
 - /dev/disk/by-diskseq/9-part16
 - /dev/disk/by-id/nvme-Amazon_Elastic_Block_Store_vol00fc4c0ecdbec535c-part16
 - /dev/disk/by-id/nvme-Amazon_Elastic_Block_Store_vol00fc4c0ecdbec535c_1-part16
 - /dev/disk/by-id/nvme-uuid.2446e143-ca43-51f8-91fb-ee0662ec7e50-part16
 - /dev/disk/by-label/BOOT
 - /dev/disk/by-partuuid/1b154230-375f-4a23-827a-0d7830f7c0c1
 - /dev/disk/by-path/pci-0000:00:04.0-nvme-1-part16
 - /dev/disk/by-uuid/d726071f-b770-48f2-8f6f-3016a0245f0f
 label: BOOT
 uuid: d726071f-b770-48f2-8f6f-3016a0245f0f
 serial-id: Amazon_Elastic_Block_Store_vol00fc4c0ecdbec535c_1
 wwn: uuid.2446e143-ca43-51f8-91fb-ee0662ec7e50
 size: 913
 fs-type: ext4
 in-use: true
 mount-point: /boot
```


## Documentation changes

No

## Links


**Jira card:** [JUJU-7267](https://warthogs.atlassian.net/browse/JUJU-7267)



[JUJU-7267]: https://warthogs.atlassian.net/browse/JUJU-7267?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

internal/migration/migration.go

@@ -93,7 +93,7 @@ func NewModelExporter(
 	logger corelogger.Logger,
 	clock clock.Clock,
 ) *ModelExporter {
-	return &ModelExporter{
+	me := &ModelExporter{
 		operationExporter:     operationExporter,
 		legacyStateExporter:   legacyStateExporter,
 		scope:                 scope,
@@ -102,6 +102,8 @@ func NewModelExporter(
 		logger:                logger,
 		clock:                 clock,
 	}
+	me.operationExporter.ExportOperations(me.storageRegistryGetter)
+	return me
 }
 
 // ExportModelPartial partially serializes a model description from the
@@ -129,7 +131,6 @@ func (e *ModelExporter) ExportModel(ctx context.Context, leaders map[string]stri
 
 // Export serializes a model description from the database contents.
 func (e *ModelExporter) Export(ctx context.Context, model description.Model) (description.Model, error) {
-	e.operationExporter.ExportOperations(e.storageRegistryGetter)
 	if err := e.coordinator.Perform(ctx, e.scope, model); err != nil {
 		return nil, errors.Trace(err)
 	}

internal/migration/migration_test.go

@@ -62,14 +62,6 @@ func (s *ExportSuite) TestExportValidates(c *gc.C) {
 	defer s.setupMocks(c).Finish()
 
 	scope := modelmigration.NewScope(nil, nil, nil)
-	exporter := migration.NewModelExporter(
-		s.operationsExporter,
-		nil,
-		scope,
-		s.storageRegistryGetter,
-		s.coordinator,
-		nil, nil,
-	)
 
 	// The order of the expectations is important here. We expect that the
 	// validation is the last thing that happens.
@@ -79,6 +71,15 @@ func (s *ExportSuite) TestExportValidates(c *gc.C) {
 		s.model.EXPECT().Validate().Return(nil),
 	)
 
+	exporter := migration.NewModelExporter(
+		s.operationsExporter,
+		nil,
+		scope,
+		s.storageRegistryGetter,
+		s.coordinator,
+		nil, nil,
+	)
+
 	_, err := exporter.Export(context.Background(), s.model)
 	c.Assert(err, jc.ErrorIsNil)
 }
@@ -87,6 +88,11 @@ func (s *ExportSuite) TestExportValidationFails(c *gc.C) {
 	defer s.setupMocks(c).Finish()
 
 	scope := modelmigration.NewScope(nil, nil, nil)
+
+	s.operationsExporter.EXPECT().ExportOperations(s.storageRegistryGetter)
+	s.model.EXPECT().Validate().Return(errors.New("boom"))
+	s.coordinator.EXPECT().Perform(gomock.Any(), scope, s.model).Return(nil)
+
 	exporter := migration.NewModelExporter(
 		s.operationsExporter,
 		nil,
@@ -96,10 +102,6 @@ func (s *ExportSuite) TestExportValidationFails(c *gc.C) {
 		nil, nil,
 	)
 
-	s.operationsExporter.EXPECT().ExportOperations(s.storageRegistryGetter)
-	s.model.EXPECT().Validate().Return(errors.New("boom"))
-	s.coordinator.EXPECT().Perform(gomock.Any(), scope, s.model).Return(nil)
-
 	_, err := exporter.Export(context.Background(), s.model)
 	c.Assert(err, gc.ErrorMatches, "boom")
 }