improve how xenapi RRD records are retrieved

[Armando Migliaccio]

There is nothing particularly wrong with how RRD records are retrieved in xenapi today.

However there are a couple of potential issues, as described below:

- RRD XMLs are always obtained using http over the XS management interface address. Albeit this is fine in most cases there are problems when: i) nova-compute domU is talking to xapi using the internal management network (e.g. talking to xapi via 169.254.0.1) and traffic cannot be routed between domU and dom0; ii) in resource pools, the host address from the xenapi session handle is always the master, which could get overloaded if there are too many requests.

- get_rrd and get_rrd_updates could politely log the IOError exceptions.

I propose to use FLAGS.xenapi_connection_url instead. By using this flag we have the following benefits:

- we transparently use the appropriate scheme and server (regardless of whether the host is in a pool or not).
- it is quicker (we don't need to call xapi to get the address)

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/4072

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/4072
Committed: http://github.com/openstack/nova/commit/00c77e0e9af6ae16484e4bee5f33de1eeb812227
Submitter: Jenkins
Branch: master

commit 00c77e0e9af6ae16484e4bee5f33de1eeb812227
Author: Armando Migliaccio <email address hidden>
Date: Mon Feb 13 18:46:57 2012 +0000

    bug 931604: improve how xenapi RRD records are retrieved

    switch to using FLAGS.xenapi_connection_url to obtain scheme and
    address to talk to in order to fetch RRD XMLs. See bug report for
    more info.

    Change-Id: Iad6520cdb15f32e9e50ab0d42026282e57aaa30d