[Openstack-operators] meta-data values stored in ??

Lorin Hochstein lorin at nimbisservices.com
Tue Aug 27 12:56:30 UTC 2013

Hi Shyam:

On Mon, Aug 26, 2013 at 7:28 AM, Shyam Goud <shyam.todeti at oneconvergence.com
> wrote:

>  Hello,
> I configured my metadata service and it works fine. I am able to inject
> ssh pub-key's to the guest VM.
> From my guest VM when i execute meta-data curl cmd, I get this below
> output.
> I know http port is mapped to metadata service on
> controller node. But i want to know where is the meta data stored in? is it
> per instance basis ?

The metadata service is implemented by the nova-api service, which handles
the metadata requests for all instances. The metadata service keeps an
in-memory cache of the metadata for all instances. If the data isn't in the
cache, nova-api does a database lookup (via conductor, if present) for the
instance metadata information.

Also the below curl cmd doesn't use any instance-id, how it is mapping to
> particular instance ?
If you are not using the quantum/neutron namespace proxy + metadata agent,
then nova-api does an instance-id lookup based on the source IP address of
the http request.

If you are using the quantum/neutron namespace proxy + metadata agent: the
namespace proxy will add the HTTP "X-Forwarded-For" HTTP header with the
source IP address of the instance and then pass the request to the metadata
agent. Then, the metadata agent will do a lookup based on the
"X-Forwarded-For" header and will add an "X-Instance-ID" header with the
instance ID. The nova-api service will then use the X-Instance-ID to
identify the instance and do the cache/database lookup.


Lorin Hochstein
Lead Architect - Cloud Services
Nimbis Services, Inc.
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