Fix PreviousGenerationInstanceType family string matching (#2558)

* fix(rule) - better approach for regex validation

PreviousGenerationInstanceType rule is currently using a validation
regex that is incorrectly targetting instance types like 'mac1.metal'
due to 'c1' being found in 'mac1.' string

Split instance type to find out which section is the family and then
perform a full 'match' instead of a 'search' on it

Family section may vary in position depending on the property attribute

* test - update test case with new instance type

* fix(rule): improve matching rule

Switch back to a full regex search approach that accomodates properties
like AWS::Redshift::Cluster NodeType without having to add exceptions
to the rule if we ever want to validate those

* fix(rule): missing capture group in regex

Co-authored-by: Pat Myron <PatMyron@users.noreply.github.com>

Co-authored-by: Pat Myron <PatMyron@users.noreply.github.com>
Co-authored-by: Kevin DeJong <kddejong@amazon.com>

src/cfnlint/rules/resources/PreviousGenerationInstanceType.py

@@ -30,8 +30,7 @@ def match(self, cfn):
                 if isinstance(
                     resource.get("Properties", {}).get(property_type, ""), str
                 ):
-                    if re.search(
-                        r"([cmr][1-3]|cc2|cg1|cr1|g2|hi1|hs1|i2|t1)\.",
+                    if self.__is_previous_generation_instance_type(
                         resource.get("Properties", {}).get(property_type, ""),
                     ):
                         matches.append(
@@ -69,8 +68,7 @@ def match(self, cfn):
                     .get(property_type, ""),
                     str,
                 ):
-                    if re.search(
-                        r"([cmr][1-3]|cc2|cg1|cr1|g2|hi1|hs1|i2|t1)\.",
+                    if self.__is_previous_generation_instance_type(
                         resource.get("Properties", {})
                         .get(top_level_property_type, {})
                         .get(property_type, ""),
@@ -91,3 +89,11 @@ def match(self, cfn):
                             )
                         )
         return matches
+
+    def __is_previous_generation_instance_type(self, instance_type):
+        return (
+            re.search(
+                r"(^|\.)([cmr][1-3]|cc2|cg1|cr1|g2|hi1|hs1|i2|t1)($|\.)", instance_type
+            )
+            is not None
+        )

test/fixtures/templates/bad/previous_generation_instances.yaml

@@ -21,3 +21,7 @@ Resources:
     Properties:
       ElasticsearchClusterConfig:
         InstanceType: m3.medium.elasticsearch
+  Host:
+    Type: AWS::EC2::Host
+    Properties:
+      InstanceType: mac1.metal