Unable to establish connection to
https://192.168.50.30:13989/v2/action_executions: ('Connection aborted.',
BadStatusLine("''",))

Did you ever solve this? We ran into the same error this week and have an answer.

In /etc/mistral/mistral.conf, change the rpc_response_timeout to 600, then sudo systemctl restart openstack-mistral*

Then in /etc/haproxy/haproxy.cfg add two lines to the `listen mistral` section:

timeout client 10m
timeout server 10m

And restart the service with `sudo systemctl restart haproxy'

-- 
MC