[Openstack] flavor extra_specs

Anne Gentle anne at openstack.org
Thu Jun 12 16:51:22 UTC 2014


On Thu, Jun 12, 2014 at 11:33 AM, Tiago Sousa <tiagu.asp at gmail.com> wrote:

> Hi, does anyone have documentation on how the extra_specs work?
>
>
There's a bit of a worked example in the Operations Guide.
>From http://docs.openstack.org/trunk/openstack-ops/content/scaling.html

An advanced use of this general concept allows different instance types to
run with different CPU and RAM allocation rations so that high-intensity
computing loads and low-intensity development and testing systems can share
the same cloud without either starving the high-use systems or wasting
resources on low-utilization systems. This works by setting metadata in
your host aggregates and matching extra_specs in your instance types.

The first step is setting the aggregate metadata keys cpu_allocation_ratio
 and ram_allocation_ration to a floating-point value. The filter schedulers
AggregateCoreFilter and AggregateRamFilter will use those values rather
than the global defaults in nova.conf when scheduling to hosts in the
aggregate. It is important to be cautious when using this feature, since
each host can be in multiple aggregates but should have only one allocation
ratio for each resources. It is up to you to avoid putting a host in
multiple aggregates that define different values for the same resource.

This is the first half of the equation. To get instance types that are
guaranteed a particular ratio, you must set theextra_specs in the instance
type to the key-value pair you want to match in the aggregate. For example,
if you defineextra specs cpu_allocation_ratio to "1.0", then instances of
that type will run in aggregates only where the metadata key
cpu_allocation_ratio is also defined as "1.0." In practice, it is better to
define an additional key-value pair in the aggregate metadata to match on
rather than match directly on cpu_allocation_ratio or core_allocation_ratio.
This allows better abstraction. For example, by defining a key overcommit and
setting a value of "high," "medium," or "low," you could then tune the
numeric allocation ratios in the aggregates without also needing to change
all instance types relating to them.


> I would like to add a serial port to a flavor, and my research pointed me
> to the extra_specs but got stuck there.
>
>
> Cheers,
> Tiago
>
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