[openstack-dev] [nova] Service group foundations and features
harlowja at outlook.com
Thu May 7 21:52:57 UTC 2015
In seeing the following:
Vilobh and I are starting to come to the conclusion that the service
group layers in nova really need to be cleaned up (without adding more
features that only work in one driver), or removed or other... Spec
has interesting findings on this:
* The zookeeper service driver in nova has probably been broken for 1 or
more releases, due to eventlet attributes that are gone that it via
evzookeeper library was using. Evzookeeper only works for eventlet <
0.17.1. Please refer to  for details.
* The memcache service driver really only uses memcache for a tiny piece
of the service liveness information (and does a database service table
scan to get the list of services). Please refer to  for details.
* Nova-manage service disable (CLI admin api) does interact with the
service group layer for the 'is_up' API (but it also does a database
service table scan to get the list of services, so this is
inconsistent with the service group driver API 'get_all' view on what
is enabled/disabled). Please refer to  for nova manage service
enable disable for details.
* Nova service delete (REST api) seems to follow a similar broken
pattern (it also avoids calling into the service group layer to delete a
service, which means it only works with the database layer, and
therefore is inconsistent with the service group 'get_all' API).
^^ Doing the above makes both disable/delete agnostic about other
backends available that may/might manage service group data for example
zookeeper, memcache, redis etc... Please refer  for details.
Ideally the API should follow the model used in  so that the
extension, admin interface as well as the API interface use the same
servicegroup interface which should be *fully* responsible for managing
services. Doing so we will have a consistent view of services data,
liveness, disabled/enabled and so-on...
So with no disrespect to the authors of 169836 and 163274 (or anyone
else involved), I am wondering if we can put a request in to figure out
how to get the foundation of the service group concepts stabilized (or
other...) before adding more features (that only work with the DB layer).
What is the path to request some kind of larger coordination effort by
the nova folks to fix the service group layers (and the concepts that
are not disjoint/don't work across them) before continuing to add
features on-top of a 'shakey' foundation?
If I could propose something it would probably work out like the following:
Step 0: Figure out if the service group API + layer(s) should be
maintained/tweaked at all (nova-core decides?)
If maintain it:
- Have an agreement that nova service extension, admin
interface(nova-manage) and API go through a common path for
* This common path should likely be the servicegroup API so as to
have a consistent view of data and that also helps nova to add different
data-stores (keeping the services data in a DB and getting numerous
updates about liveliness every few seconds of N number of compute where
N is pretty high can be detrimental to Nova's performance)
- At the same time allow 163274 to be worked on (since it fixes a
edge-case that was asked about in the initial addition of the delete API
in its initial code commit @ https://review.openstack.org/#/c/39998/)
- Delay 169836 until the above two/three are fixed (and stabilized);
it's down concept (and all other usages of services that are hitting a
database mentioned above) will need to go through the same service group
foundation that is currently being skipped.
- Discard 138607 and start removing the service group code (and just
use the DB for all the things).
- Allow 163274 and 138607 (since those would be additions on-top of
the DB layer that will be preserved).
- Josh (and Vilobh, who is spending the most time on this recently)
 Replace service group with tooz :
 Nova manage enable :
 Nova manage disable :
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