fix: map Python CRITICAL log level to OTel FATAL severity text

CHANGELOG.md

@@ -14,6 +14,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - `opentelemetry-sdk`: Add `create_resource` and `create_propagator`/`configure_propagator` to declarative file configuration, enabling Resource and propagator instantiation from config files without reading env vars
   ([#4979](https://github.com/open-telemetry/opentelemetry-python/pull/4979))
+- `opentelemetry-sdk`: Map Python `CRITICAL` log level to OTel `FATAL` severity text per the specification
+  ([#4984](https://github.com/open-telemetry/opentelemetry-python/issues/4984))
 - `opentelemetry-sdk`: Add file configuration support with YAML/JSON loading, environment variable substitution, and schema validation against the vendored OTel config JSON schema
   ([#4898](https://github.com/open-telemetry/opentelemetry-python/pull/4898))
 - Fix intermittent CI failures in `getting-started` and `tracecontext` jobs caused by GitHub git CDN SHA propagation lag by installing contrib packages from the already-checked-out local copy instead of a second git clone

opentelemetry-sdk/src/opentelemetry/sdk/_logs/_internal/__init__.py

@@ -592,10 +592,16 @@ def _translate(self, record: logging.LogRecord) -> LogRecord:
             else:
                 body = record.getMessage()
 
-        # related to https://github.com/open-telemetry/opentelemetry-python/issues/3548
-        # Severity Text = WARN as defined in https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/logs/data-model.md#displaying-severity.
-        level_name = (
-            "WARN" if record.levelname == "WARNING" else record.levelname
+        # Map Python log level names to OTel severity text as defined in
+        # https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/logs/data-model.md#displaying-severity
+        # Python "WARNING" -> OTel "WARN" (see #3548)
+        # Python "CRITICAL" -> OTel "FATAL" (see #4984)
+        _python_to_otel_severity_text = {
+            "WARNING": "WARN",
+            "CRITICAL": "FATAL",
+        }
+        level_name = _python_to_otel_severity_text.get(
+            record.levelname, record.levelname
         )
 
         return LogRecord(

opentelemetry-sdk/tests/logs/test_export.py

@@ -161,7 +161,7 @@ def test_simple_log_record_processor_custom_level(self):
             SeverityNumber.ERROR,
         )
         self.assertEqual(fatal_log_record.log_record.body, "Critical message")
-        self.assertEqual(fatal_log_record.log_record.severity_text, "CRITICAL")
+        self.assertEqual(fatal_log_record.log_record.severity_text, "FATAL")
         self.assertEqual(
             fatal_log_record.log_record.severity_number, SeverityNumber.FATAL
         )
@@ -216,7 +216,7 @@ def test_simple_log_record_processor_trace_correlation(self):
             self.assertEqual(
                 sdk_record.log_record.body, "Critical message within span"
             )
-            self.assertEqual(sdk_record.log_record.severity_text, "CRITICAL")
+            self.assertEqual(sdk_record.log_record.severity_text, "FATAL")
             self.assertEqual(
                 sdk_record.log_record.severity_number, SeverityNumber.FATAL
             )
@@ -290,7 +290,7 @@ def test_simple_log_record_processor_different_msg_types(self):
             ("Very high rise in temperatures across the globe", "ERROR"),
             (
                 "Temperature hits high 420 C in Hyderabad",
-                "CRITICAL",
+                "FATAL",
             ),
             (["list", "of", "strings"], "WARN"),
             ({"key": "value"}, "ERROR"),
@@ -386,7 +386,7 @@ def test_simple_log_record_processor_different_msg_types_with_formatter(
             ),
             (
                 "different_msg_types - CRITICAL - Temperature hits high 420 C in Hyderabad",
-                "CRITICAL",
+                "FATAL",
             ),
             (
                 "different_msg_types - WARNING - ['list', 'of', 'strings']",

opentelemetry-sdk/tests/logs/test_handler.py

@@ -341,7 +341,7 @@ def test_log_record_trace_correlation(self):
                     record.log_record.body,
                     "Critical message within span",
                 )
-                self.assertEqual(record.log_record.severity_text, "CRITICAL")
+                self.assertEqual(record.log_record.severity_text, "FATAL")
                 self.assertEqual(
                     record.log_record.severity_number,
                     SeverityNumber.FATAL,
@@ -374,7 +374,7 @@ def test_log_record_trace_correlation_deprecated(self):
             self.assertEqual(
                 record.log_record.body, "Critical message within span"
             )
-            self.assertEqual(record.log_record.severity_text, "CRITICAL")
+            self.assertEqual(record.log_record.severity_text, "FATAL")
             self.assertEqual(
                 record.log_record.severity_number, SeverityNumber.FATAL
             )

opentelemetry-sdk/tests/logs/test_multi_log_processor.py

@@ -94,9 +94,9 @@ def test_log_record_processor(self):
         provider.add_log_record_processor(processor2)
         with self.assertLogs(level=logging.CRITICAL):
             logger.critical("Something disastrous")
-        expected_list_1.append(("Something disastrous", "CRITICAL"))
+        expected_list_1.append(("Something disastrous", "FATAL"))
 
-        expected_list_2 = [("Something disastrous", "CRITICAL")]
+        expected_list_2 = [("Something disastrous", "FATAL")]
 
         self.assertEqual(logs_list_1, expected_list_1)
         self.assertEqual(logs_list_2, expected_list_2)