fix: defer boot_agent until after eventlet monkey_patch to prevent recursion error

[CagriYonca]

Problem & Root Cause

When running under Gunicorn with the eventlet worker class, Instana's early auto-instrumentation eagerly imports third-party libraries in the master process before eventlet.monkey_patch executes.

Modules such as urllib3 and pymongo capture module-level references to the unpatched ssl.SSLContext. When Eventlet subsequently patches the ssl module, ssl.SSLContext is replaced with its green subclass. Initializing SSL connections later causes super lookups inside property setters to resolve the global green subclass instead of the original class, resulting in an infinite recursion and a RecursionError.

Solution

This PR defers boot_agent execution when eventlet is present in the environment:

• Wraps eventlet.monkey_patch using wrapt.
• Defers boot_agent and all eager instrumentation imports until after eventlet.monkey_patch completes in the forked worker process.
• Suppresses sensor boot in the Gunicorn arbiter process, ensuring instrumentation runs only in worker processes.

Changes

• src/instana/__init__.py: Added _defer_boot_until_eventlet_patch to defer agent boot until worker post-patch.
• tests/frameworks/test_eventlet_autotrace.py: Added unit tests covering deferred boot registration, worker execution, and arbiter suppression.

[pvital]

Great work @CagriYonca.
I have a few considerations.

[pvital]

Let me understand here. If gevent and eventlet are used at the same time (I don't know if that's possible or not), first we apply the gevent monkey patch and then the eventlet monkey patch?

Anyway, I see some repetitive code here; I guess we can reduce this to something like (consider the change starting on line 299):

Suggested change

	# Eventlet deferred boot: if eventlet is present in the environment,
	# defer boot_agent() until after eventlet.monkey_patch() has been called
	# (which happens in each worker process after fork). This prevents the
	# ssl.SSLContext global-rebind RecursionError seen with gunicorn eventlet workers.
	if (
	(is_autowrapt_instrumented() or is_webhook_instrumented())
	and "INSTANA_DISABLE_AUTO_INSTR" not in os.environ
	and importlib_util.find_spec("eventlet")
	):
	_defer_boot_until_eventlet_patch()
	if (
	(is_autowrapt_instrumented() or is_webhook_instrumented())
	and "INSTANA_DISABLE_AUTO_INSTR" not in os.environ
	):
	# Automatic gevent monkey patching
	# unless auto instrumentation is off, then the customer should do manual gevent monkey patching
	if importlib_util.find_spec("gevent"):
	apply_gevent_monkey_patch()
	# Eventlet deferred boot: if eventlet is present in the environment,
	# defer boot_agent() until after eventlet.monkey_patch() has been called
	# (which happens in each worker process after fork). This prevents the
	# ssl.SSLContext global-rebind RecursionError seen with gunicorn eventlet workers.
	if importlib_util.find_spec("eventlet"):
	_defer_boot_until_eventlet_patch()

[CagriYonca]

I've refactored the block as you suggested, the shared condition is now extracted into a single outer block, with gevent and eventlet checks nested inside.

gevent and eventlet are not used simultaneously, these are Gunicorn's worker classes and they serve the same purpose. The two inner checks are independent branches for each case.

[GSVarsha]

If is_worker is True, boot_agent() is called twice

[GSVarsha]

Same as here

[GSVarsha]

eventlet.monkey_patch() returns None

Suggested change

	result = wrapped(*args, **kwargs)
	wrapped(*args, **kwargs)

[GSVarsha]

Suggested change

return result

Reason: same as here

[GSVarsha]

Suggested change

	) -> Optional[object]:
	) -> None:

Reason: same as here

[GSVarsha]

Suggested change

from typing import Optional

Reason: same as here

[GSVarsha]

Few requests.