deprecate eventlet monkey patch within oslo.log

Change-Id: I35797e0d03b69d77733a49c80b6e06c964fb48bf

oslo_log/log.py

@@ -38,6 +38,7 @@ try:
 except ImportError:
     syslog = None
 
+import debtcollector
 from oslo_config import cfg
 from oslo_utils import eventletutils
 from oslo_utils import importutils
@@ -275,14 +276,18 @@ def _fix_eventlet_logging():
 
     global _EVENTLET_FIX_APPLIED
 
-    # If eventlet was not loaded before call to setup assume it's not used.
-    if eventletutils.is_monkey_patched('thread') and not _EVENTLET_FIX_APPLIED:
-        import eventlet.green.threading
-        from oslo_log import pipe_mutex
-        logging.threading = eventlet.green.threading
-        logging._lock = logging.threading.RLock()
-        logging.Handler.createLock = pipe_mutex.pipe_createLock
-        _EVENTLET_FIX_APPLIED = True
+    if eventletutils.is_monkey_patched('thread'):
+        debtcollector.deprecate(
+            "Eventlet support is deprecated and will be removed")
+
+        # If eventlet was not loaded before call to setup assume it's not used.
+        if not _EVENTLET_FIX_APPLIED:
+            import eventlet.green.threading
+            from oslo_log import pipe_mutex
+            logging.threading = eventlet.green.threading
+            logging._lock = logging.threading.RLock()
+            logging.Handler.createLock = pipe_mutex.pipe_createLock
+            _EVENTLET_FIX_APPLIED = True
 
 
 def setup(conf, product_name, version='unknown', *, fix_eventlet=True):

releasenotes/notes/deprecate-eventlet-monkey_patch-f6b37295e367d6c0.yaml

@@ -0,0 +1,11 @@
+---
+deprecations:
+  - |
+    Eventlet usages are deprecated and the removal of Eventlet from
+    OpenStack `is planned <https://governance.openstack.org/tc//goals/proposed/remove-eventlet.html>`_,
+    for this reason, using oslo.log in a monkey
+    patched environment is now deprecated. The support of Eventlet will be
+    soon removed from oslo.log.
+
+    Please start considering removing your internal Eventlet usages and
+    start migrating your stack.

requirements.txt

@@ -9,3 +9,4 @@ oslo.i18n>=3.20.0 # Apache-2.0
 oslo.utils>=3.36.0 # Apache-2.0
 oslo.serialization>=2.25.0 # Apache-2.0
 python-dateutil>=2.7.0 # BSD
+debtcollector>=3.0.0 # Apache-2.0