Adding cloudformation-validate. Cfn-lint does the heavy lifting.

moto/cloudformation/models.py

@@ -13,6 +13,7 @@ from .utils import (
     generate_changeset_id,
     generate_stack_id,
     yaml_tag_constructor,
+    validate_template_cfn_lint,
 )
 from .exceptions import ValidationError
 
@@ -270,6 +271,9 @@ class CloudFormationBackend(BaseBackend):
             next_token = str(token + 100) if len(all_exports) > token + 100 else None
         return exports, next_token
 
+    def validate_template(self, template):
+        return validate_template_cfn_lint(template)
+
     def _validate_export_uniqueness(self, stack):
         new_stack_export_names = [x.name for x in stack.exports]
         export_names = self.exports.keys()

moto/cloudformation/responses.py

@@ -1,6 +1,7 @@
 from __future__ import unicode_literals
 
 import json
+import yaml
 from six.moves.urllib.parse import urlparse
 
 from moto.core.responses import BaseResponse
@@ -294,6 +295,32 @@ class CloudFormationResponse(BaseResponse):
         template = self.response_template(LIST_EXPORTS_RESPONSE)
         return template.render(exports=exports, next_token=next_token)
 
+    def validate_template(self):
+        cfn_lint = self.cloudformation_backend.validate_template(self._get_param('TemplateBody'))
+        if cfn_lint:
+            raise ValidationError(cfn_lint[0].message)
+        description = ""
+        try:
+            description = json.loads(self._get_param('TemplateBody'))['Description']
+        except (ValueError, KeyError):
+            pass
+        try:
+            description = yaml.load(self._get_param('TemplateBody'))['Description']
+        except (yaml.ParserError, KeyError):
+            pass
+        template = self.response_template(VALIDATE_STACK_RESPONSE_TEMPLATE)
+        return template.render(description=description)
+
+
+VALIDATE_STACK_RESPONSE_TEMPLATE = """<ValidateTemplateResponse>
+        <ValidateTemplateResult>
+        <Capabilities></Capabilities>
+<CapabilitiesReason></CapabilitiesReason>
+<DeclaredTransforms></DeclaredTransforms>
+<Description>{{ description }}</Description>
+<Parameters></Parameters>
+</ValidateTemplateResult>
+</ValidateTemplateResponse>"""
 
 CREATE_STACK_RESPONSE_TEMPLATE = """<CreateStackResponse>
   <CreateStackResult>

moto/cloudformation/utils.py

@@ -3,6 +3,9 @@ import uuid
 import six
 import random
 import yaml
+import os
+
+from cfnlint import decode, core
 
 
 def generate_stack_id(stack_name):
@@ -38,3 +41,33 @@ def yaml_tag_constructor(loader, tag, node):
         key = 'Fn::{}'.format(tag[1:])
 
     return {key: _f(loader, tag, node)}
+
+
+def validate_template_cfn_lint(template):
+
+    # Save the template to a temporary file -- cfn-lint requires a file
+    filename = "file.tmp"
+    with open(filename, "w") as file:
+        file.write(template)
+    abs_filename = os.path.abspath(filename)
+
+    # decode handles both yaml and json
+    template, matches = decode.decode(abs_filename, False)
+
+    # Set cfn-lint to info
+    core.configure_logging(None)
+
+    # Initialize the ruleset to be applied (no overrules, no excludes)
+    rules = core.get_rules([], [], [])
+
+    # Use us-east-1 region (spec file) for validation
+    regions = ['us-east-1']
+
+    # Process all the rules and gather the errors
+    matches = core.run_checks(
+        abs_filename,
+        template,
+        rules,
+        regions)
+
+    return matches