issues observed with multi-node setup

Lately I've been running devstack with quantum in a multi-node setup.

The controller node has pretty much everything enabled:

stackrc:

ENABLED_SERVICES=g-api,g-reg,key,n-api,n-crt,n-obj,n-cpu,n-net,n-vol,n-sch,n-novnc,n-xvnc,n-cauth,horizon,mysql,rabbit,quantum,q-agt,q-svc

I can then add multiple extra compute nodes, that run only nova-compute and quantum agent. They point to the "controller node for all services:

stackrc:

ENABLED_SERVICES=n-cpu,quantum,q-agt

localrc:

SERVICE_HOST=172.28.33.6
MYSQL_HOST=$SERVICE_HOST
RABBIT_HOST=$SERVICE_HOST

this works great, but I've noticed two quirks as wanted to ask about.

Issue #1

I noticed that when I do a clean install on a compute node, and specify only "ENABLED_SERVICES=n-cpu,quantum,q-agt", nova-compute would fail because it could not find some glance libraries (glance.common.*). Presumably its this reference:

./nova/image/glance.py:from glance.common import exception as glance_exception

This was a week or two ago, but it seems like the glance dependencies where not being installed if the glance service was not running on the node. Specifying g-api as one of the services at least once seemed sufficient to get the libraries pulled down, after which I no longer needed to specify it. Still, seems like a busted dependency.

Issue #2

this is more recent. If I only specify "ENABLED_SERVICES=n-cpu,quantum,q-agt" on a compute node, I noticed that "nova-manage service list" shows that the nova-compute on the compute-only node is not phoning home correctly. When I used screen -x stack to access the console, I noticed that nova-compute was trying to reach localhost, even though my localrc had the RABBIT_HOST variable set correctly.

I think the root cause is the following line in stack.sh:

if is_service_enabled rabbit ; then
    add_nova_opt "rabbit_host=$RABBIT_HOST"
    add_nova_opt "rabbit_password=$RABBIT_PASSWORD"

My understanding is that the "rabbit" service need only be run once per deployment (i.e., on my controller node), but this code means that unless I specify it on each node, nova-compute will assume rabbit is on localhost. I can work around this issue by specifying rabbit as an enabled service on each of my machines, and using RABBIT_HOST to point nova-compute to a single centralized server, but it seems borked, so I thought I would mention it.

Thanks!