Fixes container detector for systemd & cgroupv1 with Docker (#3429)

* Fixes container detector for systemd & cgroupv1 with Docker

* Update CHANGELOG

---------

Co-authored-by: Emídio Neto <9735060+emdneto@users.noreply.github.com>
Co-authored-by: Riccardo Magliocchetti <riccardo.magliocchetti@gmail.com>

resource/opentelemetry-resource-detector-container/src/opentelemetry/resource/detector/container/__init__.py

@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import re
 from logging import getLogger
 
 from opentelemetry.sdk.resources import Resource, ResourceDetector
@@ -31,9 +32,14 @@ def _get_container_id_v1():
         ) as container_info_file:
             for raw_line in container_info_file.readlines():
                 line = raw_line.strip()
-                if len(line) > _CONTAINER_ID_LENGTH:
-                    container_id = line[-_CONTAINER_ID_LENGTH:]
+
+                match = re.search(
+                    r"^.*/(?:.*[-:])?([0-9a-f]+)(?:\.|\s*$)", line
+                )
+                if match is not None:
+                    container_id = match.group(1)
                     break
+
     except FileNotFoundError as exception:
         logger.warning("Failed to get container id. Exception: %s", exception)
     return container_id

resource/opentelemetry-resource-detector-container/tests/test_container.py

@@ -51,6 +51,20 @@ class ContainerResourceDetectorTest(TestBase):
             actual.attributes.copy(), MockContainerResourceAttributes
         )
 
+    @patch(
+        "builtins.open",
+        new_callable=mock_open,
+        read_data=f"""0::/system.slice/docker-{MockContainerResourceAttributes[ResourceAttributes.CONTAINER_ID]}.scope
+        """,
+    )
+    def test_container_id_detect_from_cgroup_file_with_suffix(
+        self, mock_cgroup_file
+    ):
+        actual = ContainerResourceDetector().detect()
+        self.assertDictEqual(
+            actual.attributes.copy(), MockContainerResourceAttributes
+        )
+
     @patch(
         "opentelemetry.resource.detector.container._get_container_id_v1",
         return_value=None,