feat(sdk): add service.instance.id to default resource

The Python SDK did not auto-generate service.instance.id, unlike the
Java SDK and the stable semantic convention recommendation. Add it to
_DEFAULT_RESOURCE so every process gets a unique instance identity at
startup without any user configuration.

Author: sterchelen

opentelemetry-sdk/src/opentelemetry/sdk/resources/__init__.py

@@ -72,6 +72,7 @@
 from types import ModuleType
 from typing import List, Optional, Set, cast
 from urllib import parse
+from uuid import uuid4
 
 from opentelemetry.attributes import BoundedAttributes
 from opentelemetry.sdk.environment_variables import (
@@ -323,6 +324,7 @@ def to_json(self, indent: Optional[int] = 4) -> str:
         TELEMETRY_SDK_LANGUAGE: "python",
         TELEMETRY_SDK_NAME: "opentelemetry",
         TELEMETRY_SDK_VERSION: _OPENTELEMETRY_SDK_VERSION,
+        SERVICE_INSTANCE_ID: str(uuid4()),
     }
 )
 

opentelemetry-sdk/tests/resources/test_resources.py

@@ -45,6 +45,7 @@
     PROCESS_RUNTIME_DESCRIPTION,
     PROCESS_RUNTIME_NAME,
     PROCESS_RUNTIME_VERSION,
+    SERVICE_INSTANCE_ID,
     SERVICE_NAME,
     TELEMETRY_SDK_LANGUAGE,
     TELEMETRY_SDK_NAME,
@@ -88,6 +89,9 @@ def test_create(self):
             TELEMETRY_SDK_LANGUAGE: "python",
             TELEMETRY_SDK_VERSION: _OPENTELEMETRY_SDK_VERSION,
             SERVICE_NAME: "unknown_service",
+            SERVICE_INSTANCE_ID: _DEFAULT_RESOURCE.attributes[
+                SERVICE_INSTANCE_ID
+            ],
         }
 
         resource = Resource.create(attributes)
@@ -211,6 +215,9 @@ def test_immutability(self):
             TELEMETRY_SDK_LANGUAGE: "python",
             TELEMETRY_SDK_VERSION: _OPENTELEMETRY_SDK_VERSION,
             SERVICE_NAME: "unknown_service",
+            SERVICE_INSTANCE_ID: _DEFAULT_RESOURCE.attributes[
+                SERVICE_INSTANCE_ID
+            ],
         }
 
         attributes_copy = attributes.copy()