Use app as the default service name

.changesets/default-service-name-to-app.md

@@ -0,0 +1,7 @@
+---
+bump: patch
+type: change
+---
+
+Report `app` instead of `unknown` as the OpenTelemetry service name when the
+`service_name` configuration option is not set and collector mode is in use.

src/appsignal/opentelemetry.py

@@ -290,7 +290,7 @@ def _resource(config: Config) -> Resource:
             "appsignal.config.push_api_key": config.options.get("push_api_key"),
             "appsignal.config.revision": config.options.get("revision", "unknown"),
             "appsignal.config.language_integration": "python",
-            "service.name": config.options.get("service_name", "unknown"),
+            "service.name": config.options.get("service_name") or "app",
             "host.name": config.options.get("hostname", "unknown"),
             "appsignal.service.process_id": os.getpid(),
             "appsignal.config.filter_attributes": config.options.get(

tests/test_config.py

@@ -341,14 +341,23 @@ def test_opentelemetry_resource_with_defaults():
 
     # Test default values
     assert resource.attributes["appsignal.config.revision"] == "unknown"
-    assert resource.attributes["service.name"] == "unknown"
+    assert resource.attributes["service.name"] == "app"
     assert resource.attributes["appsignal.config.language_integration"] == "python"
 
     # Test that None values are excluded
     assert "appsignal.config.name" not in resource.attributes
     assert "appsignal.config.push_api_key" not in resource.attributes
 
 
+def test_opentelemetry_resource_with_none_service_name():
+    from appsignal.opentelemetry import _resource
+
+    config = Config(Options(service_name=None))
+    resource = _resource(config)
+
+    assert resource.attributes["service.name"] == "app"
+
+
 def test_set_private_environ_valid_log_path():
     cwdir = os.getcwd()
     config = Config(Options(log_path=cwdir))