fix: pull base runtime image if it doesnt exist

samcli/local/docker/lambda_image.py

@@ -663,7 +663,16 @@ def get_local_image_digest(self, image_name: str) -> Optional[str]:
         str
             Image digest, including `sha256:` prefix
         """
-        image_info = self.docker_client.images.get(image_name)
+        try:
+            image_info = self.docker_client.images.get(image_name)
+        except docker.errors.ImageNotFound:
+            # Base image not found locally, pull it for digest comparison
+            try:
+                self.docker_client.images.pull(image_name)
+                image_info = self.docker_client.images.get(image_name)
+            except docker.errors.APIError:
+                return None
+
         try:
             full_digest: str = image_info.attrs.get("RepoDigests", [None])[0]
             return full_digest.split("@")[1]

tests/unit/local/docker/test_lambda_image.py

@@ -786,6 +786,42 @@ def test_get_local_image_digest(self):
         lambda_image = LambdaImage("layer_downloader", False, False, docker_client=docker_client_mock)
         self.assertEqual("sha256:local-digest", lambda_image.get_local_image_digest("image_name"))
 
+    def test_get_local_image_digest_pulls_missing_image(self):
+        """Test that get_local_image_digest pulls the image if it's not found locally"""
+        docker_client_mock = Mock()
+
+        # First call to images.get raises ImageNotFound
+        # Second call (after pull) returns the image data
+        local_image_data = Mock(
+            attrs={
+                "RepoDigests": ["image_name@sha256:pulled-digest"],
+            },
+        )
+        docker_client_mock.images.get.side_effect = [ImageNotFound("Image not found"), local_image_data]
+        docker_client_mock.images.pull.return_value = None
+
+        lambda_image = LambdaImage("layer_downloader", False, False, docker_client=docker_client_mock)
+        result = lambda_image.get_local_image_digest("image_name")
+
+        # Should pull the image and return its digest
+        docker_client_mock.images.pull.assert_called_once_with("image_name")
+        self.assertEqual("sha256:pulled-digest", result)
+
+    def test_get_local_image_digest_handles_pull_failure(self):
+        """Test that get_local_image_digest returns None if pull fails"""
+        docker_client_mock = Mock()
+
+        # First call raises ImageNotFound, pull also fails
+        docker_client_mock.images.get.side_effect = ImageNotFound("Image not found")
+        docker_client_mock.images.pull.side_effect = APIError("Pull failed")
+
+        lambda_image = LambdaImage("layer_downloader", False, False, docker_client=docker_client_mock)
+        result = lambda_image.get_local_image_digest("image_name")
+
+        # Should attempt to pull and return None on failure
+        docker_client_mock.images.pull.assert_called_once_with("image_name")
+        self.assertIsNone(result)
+
     @parameterized.expand(
         [
             ("same-digest", "same-digest", True),