fix(internal): preserve writer configuration when forking (#3001) (#3013)

* fix(internal): preserve encoder when forking

* add fix

Co-authored-by: Brett Langdon <[email protected]>
(cherry picked from commit b5f0751)

Co-authored-by: Tahir H. Butt <[email protected]>

Author: mergify[bot]

ddtrace/internal/writer.py

@@ -258,19 +258,18 @@ def __init__(
             "Datadog-Meta-Tracer-Version": ddtrace.__version__,
         }
         self._timeout = timeout
-
-        encoding_version = (
+        self._api_version = (
             api_version or os.getenv("DD_TRACE_API_VERSION") or ("v0.4" if priority_sampler is not None else "v0.3")
         )
         try:
-            Encoder = MSGPACK_ENCODERS[encoding_version]
+            Encoder = MSGPACK_ENCODERS[self._api_version]
         except KeyError:
             raise ValueError(
-                "Unsupported encoding version: '%s'. The supported versions are: %r"
-                % (encoding_version, ", ".join(sorted(MSGPACK_ENCODERS.keys())))
+                "Unsupported api version: '%s'. The supported versions are: %r"
+                % (self._api_version, ", ".join(sorted(MSGPACK_ENCODERS.keys())))
             )
 
-        self._endpoint = "%s/traces" % encoding_version
+        self._endpoint = "%s/traces" % self._api_version
 
         self._container_info = container.get_container_info()
         if self._container_info and self._container_info.container_id:
@@ -337,14 +336,19 @@ def _set_keep_rate(self, trace):
 
     def recreate(self):
         # type: () -> AgentWriter
-        writer = self.__class__(
+        return self.__class__(
             agent_url=self.agent_url,
+            sampler=self._sampler,
             priority_sampler=self._priority_sampler,
+            processing_interval=self._interval,
+            buffer_size=self._buffer_size,
+            max_payload_size=self._max_payload_size,
+            timeout=self._timeout,
+            dogstatsd=self.dogstatsd,
+            report_metrics=self._report_metrics,
             sync_mode=self._sync_mode,
+            api_version=self._api_version,
         )
-        writer._headers = self._headers
-        writer._endpoint = self._endpoint
-        return writer
 
     def _put(self, data, headers):
         conn = get_connection(self.agent_url, self._timeout)

releasenotes/notes/fix-writer-recreate-8780a0713812efeb.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    Configure a writer thread in a child process after forking based on writer configuration from its parent process.

tests/tracer/test_writer.py

@@ -14,6 +14,7 @@
 from ddtrace.internal.compat import PY3
 from ddtrace.internal.compat import get_connection_response
 from ddtrace.internal.compat import httplib
+from ddtrace.internal.encoding import MSGPACK_ENCODERS
 from ddtrace.internal.uds import UDSHTTPConnection
 from ddtrace.internal.writer import AgentWriter
 from ddtrace.internal.writer import LogWriter
@@ -553,3 +554,24 @@ def test_bad_encoding(monkeypatch):
 
     with pytest.raises(ValueError):
         AgentWriter(agent_url="http://localhost:9126")
+
+
+@pytest.mark.parametrize(
+    "init_api_version,api_version,endpoint,encoder_cls",
+    [
+        (None, "v0.3", "v0.3/traces", MSGPACK_ENCODERS["v0.3"]),
+        ("v0.3", "v0.3", "v0.3/traces", MSGPACK_ENCODERS["v0.3"]),
+        ("v0.4", "v0.4", "v0.4/traces", MSGPACK_ENCODERS["v0.4"]),
+        ("v0.5", "v0.5", "v0.5/traces", MSGPACK_ENCODERS["v0.5"]),
+    ],
+)
+def test_writer_recreate_api_version(init_api_version, api_version, endpoint, encoder_cls):
+    writer = AgentWriter(agent_url="http://dne:1234", api_version=init_api_version)
+    assert writer._api_version == api_version
+    assert writer._endpoint == endpoint
+    assert isinstance(writer._encoder, encoder_cls)
+
+    writer = writer.recreate()
+    assert writer._api_version == api_version
+    assert writer._endpoint == endpoint
+    assert isinstance(writer._encoder, encoder_cls)