This Epic tracks our eventlet removal effort in Flamingo. The stories in this Epic will define the scope but we intentionally not trying to plan the full content of this Epic ahead of time, as we expect that the learning along the way will shape our plans.

The overarching goals is to get rid of all the Eventlet dependencies from Nova. This will be a multicycle effort tracked across multiple Epics.

We agreed on the Flamingo PTG to support both Eventlet based and Threading based nova services at least one cycle to easy the upgrade and transition to the new concurrency model.

Couple of patterns are identified to follow:

• Remove things that we don't need and has Eventlet dependencies (e.g. the Eventlet based WSGI services, the remote debugger)
• Replace direct Eventlet dependencies with standard lib equivalent constructs where the stdlib construct works for both Eventlet and native thread cases. (e.g. eventlet.sleep)
• Hide the direct Eventlet dependencies behind shallow and temporary abstraction to support selecting from the two concurrency models dynamically at service startup. (e.g. oslo.sevice backend selection with ENV vars, cooperative yield calls, pooled executor handling)

All the work will appear on the topic: https://review.opendev.org/q/topic:%22eventlet-removal%22+project:openstack/nova