cloudformation: process every StackInstances.update() target independently - #10184
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cloudformation: process every StackInstances.update() target independently#10184Sohel2309 wants to merge 1 commit into
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…ently StackInstances.update() (used by UpdateStackInstances) iterated the requested (account, region) targets and raised StackInstanceNotFound as soon as it hit the first target with no existing instance. This abandoned the rest of the batch, so any target listed after the missing one never got updated even though it had an existing instance and should have been - the outcome depended entirely on request-list ordering, which isn't how AWS documents this operation (each account/Region target is modeled as succeeding or failing independently within a single operation). Update every existing target first, then raise StackInstanceNotFoundException for the operation as a whole if any target was missing, so the exception is still surfaced but no longer at the cost of silently dropping updates to other, valid targets. Fixes getmoto#10173 Regression test added that updates two targets where the first one listed is missing and the second one has an existing instance, and asserts the existing instance is still updated despite the exception. Verified the new test fails with the old code (existing instance's ParameterOverrides stays unset) and passes with the fix.
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Summary
StackInstances.update()raisedStackInstanceNotFoundas soon as it encountered the first missing account/region target, causing valid targets later in the same request to be skipped.This made the result depend on the ordering of the requested targets.
Root cause
StackInstances.update()iterated through the requested account/region combinations and raisedStackInstanceNotFoundimmediately when a matching stack instance was not found.Because the exception was raised inside the loop, the remaining targets were never processed.
Fix
Update all existing targets first while tracking whether any requested target was missing.
After all targets have been processed, raise
StackInstanceNotFoundif at least one target was missing.This preserves the existing error behavior while ensuring valid targets are not silently skipped.
Regression test
Added a regression test covering the ordering-sensitive case where:
StackInstanceNotFoundException.The test fails against the original implementation and passes with the fix.
Validation
ruff format --check: passed.mypyon the modified production file: passed.Fixes #10173