diff --git a/pkg/workloads/cortex/serve/serve.py b/pkg/workloads/cortex/serve/serve.py
index af2a548d2e..44f322775c 100644
--- a/pkg/workloads/cortex/serve/serve.py
+++ b/pkg/workloads/cortex/serve/serve.py
@@ -42,7 +42,7 @@ def start(args):
     assert_api_version()
     storage = S3(bucket=os.environ["CORTEX_BUCKET"], region=os.environ["AWS_REGION"])
     try:
-        raw_api_spec = get_spec(args.cache_dir, args.spec)
+        raw_api_spec = get_spec(storage, args.cache_dir, args.spec)
         api = API(storage=storage, cache_dir=args.cache_dir, **raw_api_spec)
         client = api.predictor.initialize_client(args)
         cx_logger().info("loading the predictor from {}".format(api.predictor.path))
@@ -122,7 +122,7 @@ def after_request(response):
     try:
         api.post_latency_metrics(response.status_code, g.start_time)
 
-        if api.tracker is not None:
+        if int(response.status_code / 100) == 2 and api.tracker is not None:
             predicted_value = api.tracker.extract_predicted_value(prediction)
             api.post_tracker_metrics(predicted_value)
             if predicted_value is not None and predicted_value not in local_cache["class_set"]:
@@ -164,10 +164,10 @@ def assert_api_version():
         )
 
 
-def get_spec(cache_dir, s3_path):
+def get_spec(storage, cache_dir, s3_path):
     local_spec_path = os.path.join(cache_dir, "api_spec.msgpack")
-    bucket, key = S3.deconstruct_s3_path(s3_path)
-    S3(bucket, client_config={}).download_file(key, local_spec_path)
+    _, key = S3.deconstruct_s3_path(s3_path)
+    storage.download_file(key, local_spec_path)
     return util.read_msgpack(local_spec_path)