refactor(hook_gunicorn): added gunicorn support to otel

Signed-off-by: Cagri Yonca <[email protected]>

src/instana/__init__.py

@@ -205,7 +205,7 @@ def boot_agent() -> None:
         )
 
     # Hooks
-    from instana.hooks import hook_uwsgi  # noqa: F401
+    from instana.hooks import hook_uwsgi, hook_gunicorn  # noqa: F401
 
 
 if "INSTANA_DISABLE" not in os.environ:

src/instana/hooks/hook_gunicorn.py

@@ -0,0 +1,25 @@
+# (c) Copyright IBM Corp. 2021
+# (c) Copyright Instana Inc. 2019
+
+try:
+    from instana.log import logger
+    from instana.singletons import agent
+
+    import gunicorn
+    from gunicorn.arbiter import Arbiter
+    from gunicorn.config import Config
+    from gunicorn.workers.sync import SyncWorker
+
+    def pre_fork(config: Config, server: Arbiter, worker: SyncWorker) -> None:
+        """This is our gunicorn hook to detect and act when worker processes are forked off."""
+        logger.debug("Handling gunicorn fork...")
+        agent.handle_fork()
+
+    Config.pre_fork = pre_fork
+
+    logger.debug("Gunicorn pre-fork hook applied")
+except ImportError:
+    logger.debug(
+        "gunicorn hooks: decorators not available: likely not running under gunicorn"
+    )
+    pass