Fix: 502 response caused by Function not found during alias updates (#7883)

scripts/delete_older_function_versions.py

@@ -1,5 +1,5 @@
 """
-Delete all versions of a Lambda function prior to the specified one.
+Delete Lambda function versions older than a specified version
 """
 import argparse
 import logging
@@ -36,13 +36,18 @@ def main(argv: list[str]):
     parser.add_argument('--function-version', '-v',
                         type=int,
                         required=True,
-                        help='The Lambda function version to keep. Must be an '
-                             'integer.')
+                        help='A numeric version of the Lambda function. The '
+                             'specified version will be kept, as will '
+                             'the preceding one. All versions preceding those '
+                             'two versions will be deleted.')
     args = parser.parse_args(argv)
-    log.info('Deleting function %r versions older than %r',
-             args.function_name, args.function_version)
     functions = LambdaFunctions()
-    functions.delete_older_versions(args.function_name, args.function_version)
+    functions.delete_older_versions(args.function_name,
+                                    args.function_version,
+                                    # Keep a previous version to guard against a
+                                    # race condition due to eventual consistency
+                                    # of alias updates.
+                                    num_older_versions_to_keep=1)
 
 
 if __name__ == '__main__':

src/azul/lambdas.py

@@ -116,15 +116,28 @@ def list_functions(self) -> list[LambdaFunction]:
             for function in response['Functions']
         ]
 
-    def delete_older_versions(self, function_name: str, keep_version: int) -> None:
+    def delete_older_versions(self,
+                              function_name: str,
+                              function_version: int,
+                              *,
+                              num_older_versions_to_keep: int = 0
+                              ) -> None:
         """
-        Delete all versions of a Lambda function prior to the specified one.
+        Delete Lambda function versions older than the specified version.
 
         :param function_name: The fully qualified name of the function
                               e.g. 'azul-service-dev'
 
-        :param keep_version: The version of the function to not delete.
+        :param function_version: The version of the function to keep.
+
+        :param num_older_versions_to_keep: The number of versions older than
+                                           `function_version` to also keep.
         """
+        assert num_older_versions_to_keep >= 0, R(
+            'num_older_versions_to_keep must be non-negative', num_older_versions_to_keep)
+        keep_version = function_version - num_older_versions_to_keep
+        log.info('Deleting function %r versions older than %r',
+                 function_name, keep_version)
         paginator = self._lambda.get_paginator('list_versions_by_function')
         versions = [
             function['Version']