Kevin Benton wrote:
So IIUC tooz would be handling the liveness detection for the agents.
That would be nice to get ride of that logic in Neutron and just
register callbacks for rescheduling the dead.
Where does it store that state, does it persist timestamps to the DB
like Neutron does? If so, how would that scale better? If not, who does
a given node ask to know if an agent is online or offline when making a
scheduling decision?
Timestamps are just one way (and likely the most primitive), using redis
(or memcache) key/value and expiry are another (and letting memcache or
redis expire using its own internal algorithms), using zookeeper
ephemeral nodes[1] are another... The point being that its backend
specific and tooz supports varying backends.
However, before (what I assume is) the large code change to implement
tooz, I would like to quantify that the heartbeats are actually a
bottleneck. When I was doing some profiling of them on the master branch
a few months ago, processing a heartbeat took an order of magnitude less
time (<50ms) than the 'sync routers' task of the l3 agent (~300ms). A
few query optimizations might buy us a lot more headroom before we have
to fall back to large refactors.
Sure, always good to avoid prematurely optimizing things...
Although this is relevant for u I think anyway:
https://review.openstack.org/#/c/138607/ (same thing/nearly same in nova)...
https://review.openstack.org/#/c/172502/ (a WIP implementation of the
latter).
[1]
https://zookeeper.apache.org/doc/trunk/zookeeperProgrammers.html#Ephemeral+Nodes
Kevin Benton wrote:
One of the most common is the heartbeat from each agent. However, I
don't think we can't eliminate them because they are used to determine
if the agents are still alive for scheduling purposes. Did you have
something else in mind to determine if an agent is alive?
Put each agent in a tooz[1] group; have each agent periodically
heartbeat[2], have whoever needs to schedule read the active members of
that group (or use [3] to get notified via a callback), profit...
Pick from your favorite (supporting) driver at:
http://docs.openstack.org/__developer/tooz/compatibility.__html
<http://docs.openstack.org/developer/tooz/compatibility.html>
[1]
http://docs.openstack.org/__developer/tooz/compatibility.__html#grouping
<http://docs.openstack.org/developer/tooz/compatibility.html#grouping>
[2]
https://github.com/openstack/__tooz/blob/0.13.1/tooz/__coordination.py#L315
<https://github.com/openstack/tooz/blob/0.13.1/tooz/coordination.py#L315>
[3]
http://docs.openstack.org/__developer/tooz/tutorial/group___membership.html#watching-__group-changes
<http://docs.openstack.org/developer/tooz/tutorial/group_membership.html#watching-group-changes>
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