add support for Exports/Imports in CFn v2 by pinzon · Pull Request #12906 · localstack/localstack

pinzon · 2025-07-24T21:56:22Z

Motivation

This PR enables the functionality of Exports/Imports in CFn v2

Changes

Implement ListExports operation
ChangeSetModelExecutor stores output values that also define an Export name.
ChangeSetPreproc is able to resolve imports

Testing

Unskipped tests

Todo

2 exports cannot use the same name in the same template
An export cannot be registered if the name already exists in the exports store.

github-actions · 2025-07-24T22:06:27Z

Test Results - Preflight, Unit

22 063 tests ±0 20 329 ✅ ±0 6m 14s ⏱️ -11s
1 suites ±0 1 734 💤 ±0
1 files ±0 0 ❌ ±0

Results for commit d33106a. ± Comparison against base commit 6e03b92.

♻️ This comment has been updated with latest results.

github-actions · 2025-07-24T22:13:04Z

LocalStack Community integration with Pro

2 files 2 suites 22m 29s ⏱️
541 tests 329 ✅ 212 💤 0 ❌
543 runs 329 ✅ 214 💤 0 ❌

Results for commit d33106a.

♻️ This comment has been updated with latest results.

github-actions · 2025-07-24T22:15:25Z

Test Results (amd64) - Acceptance

7 tests ±0 5 ✅ ±0 3m 6s ⏱️ -12s
1 suites ±0 2 💤 ±0
1 files ±0 0 ❌ ±0

Results for commit d33106a. ± Comparison against base commit 6e03b92.

♻️ This comment has been updated with latest results.

github-actions · 2025-07-24T22:20:00Z

Test Results (amd64) - Integration, Bootstrap

5 files 5 suites 33m 18s ⏱️
565 tests 354 ✅ 211 💤 0 ❌
571 runs 354 ✅ 217 💤 0 ❌

Results for commit d33106a.

♻️ This comment has been updated with latest results.

simonrw

Thanks for adding these changes. The blocker is filtering the stacks by status. Perhaps we can add a test for this case as well, i.e. create two stacks with exports, delete one stack then call list_exports?

localstack-core/localstack/services/cloudformation/stores.py

localstack-core/localstack/services/cloudformation/engine/v2/change_set_model_preproc.py

localstack-core/localstack/services/cloudformation/stores.py

pinzon · 2025-07-25T15:53:40Z

Thanks for the comments. after implementing the changes the feature code feels much better 👍

simonrw

Thanks for taking another stab at this, I think we have to move the behaviour of the ImportValue implementation to the executor, and I really think we should make the exports in the store consistent with other fields there (add a _v2 dictionary).

simonrw · 2025-07-29T13:23:58Z

localstack-core/localstack/services/cloudformation/engine/v2/change_set_model_preproc.py

+    def visit_node_intrinsic_function_fn_import_value(
+        self, node_intrinsic_function: NodeIntrinsicFunction
+    ) -> PreprocEntityDelta:
+        def _compute_fn_import_value(string) -> str:
+            if not isinstance(string, str):
+                raise RuntimeError(f"Invalid parameter for import: '{string}'")
+
+            exports = exports_map(
+                account_id=self._change_set.account_id, region_name=self._change_set.region_name
+            )
+            if not exports.get(string):
+                raise RuntimeError(f"Value not found for import: '{string}'")
+
+            return exports.get(string)["Value"]
+
+        arguments_delta = self.visit(node_intrinsic_function.arguments)
+        delta = self._cached_apply(
+            scope=node_intrinsic_function.scope,
+            arguments_delta=arguments_delta,
+            resolver=_compute_fn_import_value,
+        )
+        return delta
+


issue: I think this lookup happens only in the executor. For example when describing a change set, the import is not retrieved.

I can reproduce this by

creating a change set including an ImportValue, e.g.

Resources: MyFoo: Type: AWS::SSM::Parameter Properties: Type: String Value: !ImportValue MyGlobalExportValue

describing the change set with aws describe-change-set ... --include-property-values
On AWS the Value field is KNOWN_AFTER_APPLY, but on LocalStack this code crashes because the export is fetched (but doesn't exist).

Can we add a test to cover this behaviour and implement the correct behaviour in the executor only.

I added a test and it passes with the functionality in the Preproc. maybe I'm not understanding correctly the issue.

localstack-core/localstack/services/cloudformation/stores.py

localstack-bot · 2025-07-31T20:50:12Z

Currently, only patch changes are allowed on main. Your PR labels (semver: minor) indicate that it cannot be merged into the main at this time.

coveralls · 2025-07-31T21:39:48Z

coverage: 66.357% (-20.5%) from 86.885%
when pulling 5234e4e on cp/cfn/v2/import-exports
into f5d850d on main.

simonrw

I have reviewed the tests again and think we are missing a scenario that I encountered that this test does not cover. It also explains my reasoning in this message: what if the export does not exist?

I had deployed a stack and the export did not exist. The change set was still created but there were the following differences:

in the Changes array the after context was a stringified JSON object including {{changeSet:KNOWN_AFTER_APPLY}} for the value

    "Changes": [
        {
            "Type": "Resource",
            "ResourceChange": {
                "Action": "Add",
                "LogicalResourceId": "MyFoo",
                "ResourceType": "AWS::SSM::Parameter",
                "Scope": [],
                "Details": [],
                "AfterContext": "{\"Properties\":{\"Value\":\"{{changeSet:KNOWN_AFTER_APPLY}}\",\"Type\":\"String\"}}"
            }
        }
    ],

The StatusReason contained the following message: [WARN] --include-property-values option can return incomplete ChangeSet data because: ChangeSet creation failed for resource [MyFoo] because: No export named MyGlobalExportValue

Actually there is another test case that would be interesting:

create change set that imports from an export that does not exist
deploy the stack with the export
execute the first change set

I don't think we need 100% parity here, but it's certainly an interesting case.

So in summary:

it's ok to create and describe a change set that imports values that have not been exported
it's not ok to execute a change set that references exports that don't exist
it's possible imports are looked up both during the modelling phase and execution phase, depending on the results of adding my second test suggestion

tests/aws/services/cloudformation/test_change_sets_exports_imports.py

tests/aws/services/cloudformation/api/test_transformers.py

tests/aws/services/cloudformation/test_change_sets_exports_imports.py

tests/aws/services/cloudformation/test_template_engine.py

simonrw · 2025-08-05T10:16:42Z

@pinzon I have added a commit that includes both scenarios I was thinking of. Now we have coverage of:

create stack with export, create change set using export, describe change set, execute change set, describe stack
create change set using (missing) export, describe change set, execute change set (which fails), describe failed stack
create change set using (missing) export, describe change set, create stack with export, execute change set, describe (successful) stack using export
I had to add some minor additional skips that I think are ok for now, and merged main into this branch to pick up add testing for Fn::Transform in CFn v2 #12689 that I merged this morning. If this PR is green I will approve and merge, thanks!

pinzon marked this pull request as ready for review July 24, 2025 21:56

pinzon requested review from dominikschubert and simonrw as code owners July 24, 2025 21:56

pinzon added the semver: minor Non-breaking changes which can be included in minor releases, but not in patch releases label Jul 24, 2025

simonrw requested changes Jul 25, 2025

View reviewed changes

pinzon force-pushed the cp/cfn/v2/import-exports branch from 42c4e41 to 2e34cb0 Compare July 25, 2025 15:52

pinzon requested a review from simonrw July 25, 2025 15:53

pinzon added this to the Playground milestone Jul 28, 2025

simonrw modified the milestones: Playground, 4.8 Jul 29, 2025

simonrw requested changes Jul 29, 2025

View reviewed changes

pinzon force-pushed the cp/cfn/v2/import-exports branch from 2e34cb0 to d7de3b3 Compare July 29, 2025 19:01

pinzon requested a review from simonrw July 29, 2025 21:01

pinzon added 5 commits August 1, 2025 10:38

add support for Exports/Imports in CFn v2

0b87090

refactor and improvements

4b31650

refactor exports storage

5fbf96d

new test implementation

de007d9

add skips to make snapshot pass

3cce2cb

pinzon force-pushed the cp/cfn/v2/import-exports branch from b0acf1b to 3cce2cb Compare August 1, 2025 15:43

pinzon added 2 commits August 1, 2025 12:12

fix snapshot and template

624782e

add skips

7cd40c2

simonrw reviewed Aug 4, 2025

View reviewed changes

fix tests and markers

2bb48f9

pinzon added 2 commits August 4, 2025 17:59

implement handling of missing export in describer

77c4282

fix import

3837e89

pinzon requested a review from simonrw August 4, 2025 23:10

pinzon and others added 3 commits August 4, 2025 18:12

fix linting

5234e4e

Handle different import/export cases

81c2ab3

Merge branch 'main' into cp/cfn/v2/import-exports

d33106a

simonrw approved these changes Aug 5, 2025

View reviewed changes

simonrw merged commit b411538 into main Aug 5, 2025
39 checks passed

simonrw deleted the cp/cfn/v2/import-exports branch August 5, 2025 10:58

simonrw mentioned this pull request Aug 6, 2025

CFnv2: implement SSM parameter resolving #12934

Merged

simonrw mentioned this pull request Sep 5, 2025

CFNV2: Switch provider defaults to new engine #13098

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pinzon commented Jul 24, 2025

Motivation

Changes

Testing

Todo

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