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Fix: Return proper client error for invalid YAML template structure #13300

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Merged
merged 5 commits into from
Oct 28, 2025
Merged

Fix: Return proper client error for invalid YAML template structure #13300

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0816a2f
Add test for creating a CloudFormation stack from a template
Ganji00 Oct 22, 2025
0f23737
Fix snapshot after rebase
Ganji00 Oct 22, 2025
7d03903
handle invalid TemplateBody in create_stack cfn
Ganji00 Oct 23, 2025
400858e
remove unused template
Ganji00 Oct 23, 2025
8b40b54
validate against AWS
Ganji00 Oct 23, 2025
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11 changes: 9 additions & 2 deletions localstack-core/localstack/services/cloudformation/engine/yaml_parser.py
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Original file line number Diff line number Diff line change
@@ -1,5 +1,7 @@
import yaml

from localstack.services.cloudformation.engine.validations import ValidationError


def construct_raw(_, node):
return node.value
Expand Down Expand Up @@ -60,5 +62,10 @@ def shorthand_constructor(loader: yaml.Loader, tag_suffix: str, node: yaml.Node)
yaml.add_multi_constructor("!", shorthand_constructor, customloader)


def parse_yaml(input_data: str):
return yaml.load(input_data, customloader)
def parse_yaml(input_data: str) -> dict:
parsed = yaml.load(input_data, Loader=customloader)

if not isinstance(parsed, dict):
raise ValidationError("Template format error: unsupported structure.")

return parsed
12 changes: 12 additions & 0 deletions tests/aws/services/cloudformation/api/test_stacks.py
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Expand Up @@ -183,6 +183,18 @@ def test_stack_name_creation(self, deploy_cfn_template, snapshot, aws_client):

snapshot.match("stack_response", e.value.response)

@markers.aws.validated
def test_create_stack_url_as_template(self, snapshot, aws_client):
snapshot.add_transformer(snapshot.transform.cloudformation_api())

stack_name = f"stack-{short_uid()}"

template_url = "https://raw.githubusercontent.com/aws-cloudformation/aws-cloudformation-templates/refs/heads/main/EC2/InstanceWithCfnInit.yaml"

with pytest.raises(ClientError) as e:
aws_client.cloudformation.create_stack(StackName=stack_name, TemplateBody=template_url)
snapshot.match("stack_create_ec2", e.value)

@markers.aws.validated
@pytest.mark.parametrize("fileformat", ["yaml", "json"])
def test_get_template_using_create_stack(self, snapshot, fileformat, aws_client):
Expand Down
6 changes: 6 additions & 0 deletions tests/aws/services/cloudformation/api/test_stacks.snapshot.json
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Original file line number Diff line number Diff line change
Expand Up @@ -4347,5 +4347,11 @@
]
}
}
},
"tests/aws/services/cloudformation/api/test_stacks.py::TestStacksApi::test_create_stack_url_as_template": {
"recorded-date": "23-10-2025, 19:25:10",
"recorded-content": {
"stack_create_ec2": "An error occurred (ValidationError) when calling the CreateStack operation: Template format error: unsupported structure."
}
}
}
9 changes: 9 additions & 0 deletions tests/aws/services/cloudformation/api/test_stacks.validation.json
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Original file line number Diff line number Diff line change
@@ -1,4 +1,13 @@
{
"tests/aws/services/cloudformation/api/test_stacks.py::TestStacksApi::test_create_stack_url_as_template": {
"last_validated_date": "2025-10-23T19:25:10+00:00",
"durations_in_seconds": {
"setup": 0.82,
"call": 0.82,
"teardown": 0.02,
"total": 1.66
}
},
"tests/aws/services/cloudformation/api/test_stacks.py::TestStacksApi::test_failure_options_for_stack_update[False-2]": {
"last_validated_date": "2024-06-25T17:21:51+00:00"
},
Expand Down
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