================== fails with python3.8 ==================
# systemctl status nova-api-metadata
● nova-api-metadata.service - OpenStack Compute metadata API
     Loaded: loaded (/lib/systemd/system/nova-api-metadata.service; enabled; vendor preset: enabled)
     Active: active (running) since Wed 2020-02-12 19:56:57 UTC; 2s ago
   Main PID: 20958 (nova-api-metada)
      Tasks: 5 (limit: 13942)
     Memory: 134.4M
     CGroup: /system.slice/nova-api-metadata.service
             ├─20958 /usr/bin/python3 /usr/bin/nova-api-metadata --config-file=/etc/nova/nova.conf --log-file=/var/log/nova/nova-api-metadata.log
             ├─20965 /usr/bin/python3 /usr/bin/nova-api-metadata --config-file=/etc/nova/nova.conf --log-file=/var/log/nova/nova-api-metadata.log
             ├─20966 /usr/bin/python3 /usr/bin/nova-api-metadata --config-file=/etc/nova/nova.conf --log-file=/var/log/nova/nova-api-metadata.log
             ├─20967 /usr/bin/python3 /usr/bin/nova-api-metadata --config-file=/etc/nova/nova.conf --log-file=/var/log/nova/nova-api-metadata.log
             └─20968 /usr/bin/python3 /usr/bin/nova-api-metadata --config-file=/etc/nova/nova.conf --log-file=/var/log/nova/nova-api-metadata.log

Feb 12 19:56:59 autopkgtest-lxd-osfnks nova-api-metadata[20967]: Exception ignored in: <function _after_fork at 0x7f1100d075e0>
Feb 12 19:56:59 autopkgtest-lxd-osfnks nova-api-metadata[20967]: Traceback (most recent call last):
Feb 12 19:56:59 autopkgtest-lxd-osfnks nova-api-metadata[20967]:   File "/usr/lib/python3.8/threading.py", line 1454, in _after_fork
Feb 12 19:56:59 autopkgtest-lxd-osfnks nova-api-metadata[20967]:     assert len(_active) == 1
Feb 12 19:56:59 autopkgtest-lxd-osfnks nova-api-metadata[20967]: AssertionError:
Feb 12 19:56:59 autopkgtest-lxd-osfnks nova-api-metadata[20968]: Exception ignored in: <function _after_fork at 0x7f1100d075e0>
Feb 12 19:56:59 autopkgtest-lxd-osfnks nova-api-metadata[20968]: Traceback (most recent call last):
Feb 12 19:56:59 autopkgtest-lxd-osfnks nova-api-metadata[20968]:   File "/usr/lib/python3.8/threading.py", line 1454, in _after_fork
Feb 12 19:56:59 autopkgtest-lxd-osfnks nova-api-metadata[20968]:     assert len(_active) == 1
Feb 12 19:56:59 autopkgtest-lxd-osfnks nova-api-metadata[20968]: AssertionError:

======================== switch to python 3.7 ==================
# ls -al /usr/bin/python3
lrwxrwxrwx 1 root root 18 Feb 12 19:56 /usr/bin/python3 -> /usr/bin/python3.8
# sudo rm -rf /usr/bin/python3
# sudo ln -s /usr/bin/python3.7 /usr/bin/python3
# ls -al /usr/bin/python3
lrwxrwxrwx 1 root root 18 Feb 12 19:57 /usr/bin/python3 -> /usr/bin/python3.7

======================== seems ok with python 3.7 ==================
# sudo systemctl restart nova-api-metadata
# systemctl status nova-api-metadata
● nova-api-metadata.service - OpenStack Compute metadata API
     Loaded: loaded (/lib/systemd/system/nova-api-metadata.service; enabled; vendor preset: enabled)
     Active: active (running) since Wed 2020-02-12 19:57:50 UTC; 8s ago
   Main PID: 21023 (nova-api-metada)
      Tasks: 5 (limit: 13942)
     Memory: 147.1M
     CGroup: /system.slice/nova-api-metadata.service
             ├─21023 /usr/bin/python3 /usr/bin/nova-api-metadata --config-file=/etc/nova/nova.conf --log-file=/var/log/nova/nova-api-metadata.log
             ├─21032 /usr/bin/python3 /usr/bin/nova-api-metadata --config-file=/etc/nova/nova.conf --log-file=/var/log/nova/nova-api-metadata.log
             ├─21033 /usr/bin/python3 /usr/bin/nova-api-metadata --config-file=/etc/nova/nova.conf --log-file=/var/log/nova/nova-api-metadata.log
             ├─21034 /usr/bin/python3 /usr/bin/nova-api-metadata --config-file=/etc/nova/nova.conf --log-file=/var/log/nova/nova-api-metadata.log
             └─21035 /usr/bin/python3 /usr/bin/nova-api-metadata --config-file=/etc/nova/nova.conf --log-file=/var/log/nova/nova-api-metadata.log

Feb 12 19:57:50 autopkgtest-lxd-osfnks systemd[1]: Started OpenStack Compute metadata API.
# systemctl status nova-api-metadata
● nova-api-metadata.service - OpenStack Compute metadata API
     Loaded: loaded (/lib/systemd/system/nova-api-metadata.service; enabled; vendor preset: enabled)
     Active: active (running) since Wed 2020-02-12 19:57:50 UTC; 51s ago
   Main PID: 21023 (nova-api-metada)
      Tasks: 5 (limit: 13942)
     Memory: 147.3M
     CGroup: /system.slice/nova-api-metadata.service
             ├─21023 /usr/bin/python3 /usr/bin/nova-api-metadata --config-file=/etc/nova/nova.conf --log-file=/var/log/nova/nova-api-metadata.log
             ├─21032 /usr/bin/python3 /usr/bin/nova-api-metadata --config-file=/etc/nova/nova.conf --log-file=/var/log/nova/nova-api-metadata.log
             ├─21033 /usr/bin/python3 /usr/bin/nova-api-metadata --config-file=/etc/nova/nova.conf --log-file=/var/log/nova/nova-api-metadata.log
             ├─21034 /usr/bin/python3 /usr/bin/nova-api-metadata --config-file=/etc/nova/nova.conf --log-file=/var/log/nova/nova-api-metadata.log
             └─21035 /usr/bin/python3 /usr/bin/nova-api-metadata --config-file=/etc/nova/nova.conf --log-file=/var/log/nova/nova-api-metadata.log

Feb 12 19:57:50 autopkgtest-lxd-osfnks systemd[1]: Started OpenStack Compute metadata API.

======================== patch nova's eventlet code ==================

# sudo vi /usr/lib/python3/dist-packages/nova/monkey_patch.py ## apply the following patch ##
diff --git a/nova/monkey_patch.py b/nova/monkey_patch.py
index a07ff91dac..bb7252c643 100644
--- a/nova/monkey_patch.py
+++ b/nova/monkey_patch.py
@@ -59,6 +59,9 @@ def _monkey_patch():
     else:
         eventlet.monkey_patch()
 
+    import __original_module_threading
+    import threading
+    __original_module_threading.current_thread.__globals__['_active'] = threading._active
     # NOTE(rpodolyaka): import oslo_service first, so that it makes eventlet
     # hub use a monotonic clock to avoid issues with drifts of system time (see

======================== and switch to python 3.8 ==================

# sudo rm -rf /usr/bin/python3
# sudo ln -s /usr/bin/python3.8 /usr/bin/python3
# ls -al /usr/bin/python3
lrwxrwxrwx 1 root root 18 Feb 12 20:08 /usr/bin/python3 -> /usr/bin/python3.8     # LP 1510234 for details)

======================== seems ok with python 3.8 now ==================

# sudo systemctl restart nova-api-metadata
# sudo systemctl status nova-api-metadata
● nova-api-metadata.service - OpenStack Compute metadata API
     Loaded: loaded (/lib/systemd/system/nova-api-metadata.service; enabled; vendor preset: enabled)
     Active: active (running) since Wed 2020-02-12 20:10:19 UTC; 2min 46s ago
   Main PID: 21788 (nova-api-metada)
      Tasks: 5 (limit: 13942)
     Memory: 134.3M
     CGroup: /system.slice/nova-api-metadata.service
             ├─21788 /usr/bin/python3 /usr/bin/nova-api-metadata --config-file=/etc/nova/nova.conf --log-file=/var/log/nova/nova-api-metadata.log
             ├─21893 /usr/bin/python3 /usr/bin/nova-api-metadata --config-file=/etc/nova/nova.conf --log-file=/var/log/nova/nova-api-metadata.log
             ├─21894 /usr/bin/python3 /usr/bin/nova-api-metadata --config-file=/etc/nova/nova.conf --log-file=/var/log/nova/nova-api-metadata.log
             ├─21895 /usr/bin/python3 /usr/bin/nova-api-metadata --config-file=/etc/nova/nova.conf --log-file=/var/log/nova/nova-api-metadata.log
             └─21896 /usr/bin/python3 /usr/bin/nova-api-metadata --config-file=/etc/nova/nova.conf --log-file=/var/log/nova/nova-api-metadata.log

Feb 12 20:10:19 autopkgtest-lxd-osfnks systemd[1]: Started OpenStack Compute metadata API.