opentelemetry-sdk-extension-aws: make ecs detector less chatty

Don't print warnings if we are not running inside an ecs instance so we can load the
resource detector more generally and avoid warnings in stderr.

sdk-extension/opentelemetry-sdk-extension-aws/src/opentelemetry/sdk/extension/aws/resource/ecs.py

@@ -41,9 +41,7 @@ def detect(self) -> "Resource":
             if not os.environ.get(
                 "ECS_CONTAINER_METADATA_URI"
             ) and not os.environ.get("ECS_CONTAINER_METADATA_URI_V4"):
-                raise RuntimeError(
-                    "Missing ECS_CONTAINER_METADATA_URI therefore process is not on ECS."
-                )
+                return Resource.get_empty()
 
             container_id = ""
             try:

sdk-extension/opentelemetry-sdk-extension-aws/tests/resource/test_ecs.py

@@ -79,6 +79,11 @@ def _http_get_function_fargate(url: str, *args, **kwargs) -> str:
 
 
 class AwsEcsResourceDetectorTest(unittest.TestCase):
+    @patch.dict("os.environ", {}, clear=True)
+    def test_not_on_ecs(self):
+        actual = AwsEcsResourceDetector().detect()
+        self.assertDictEqual(actual.attributes.copy(), {})
+
     @patch.dict(
         "os.environ",
         {"ECS_CONTAINER_METADATA_URI": "mock-uri"},