scale servers - vcpus and memory

Registered by Ahmed El-Khouly

Problem description
===================
Some application domains can benefit from dynamically scaling up(down) vcpus and memory with minimal impact to service provided.

Use Cases
----------
1. Singleton servers:
     Some central nova servers needs to respond to load change by adding vcpus and memory in high-load times or removing resources for down times.
2. Some servers can service preassigned service areas which can have temporary increase in loads. It will not be easy scale out as this require significant change to application architecture to redistribute services dynamically to other servers.
3. Need to face temporary changes in load without the need to use more IP addresses and transport resources needed by a scaling out solution.

Project Priority
-----------------

Does this blueprint fit under one of the :ref:`kilo-priorities`? If so which
one and how?

Proposed change
===============
1. Introduce maximum number of virtual Cpus and memory in flavor extra-spec or image meta-data. These definitions sets the upper limits for scale operation on servers. If upper limits is defined in both the flavor or the image metadata, image definitions take precedence given that they are lower than the flavor limits. All values are optional, and absence of scale upper limits makes the a server instantiated with such flavor and image non-scalable.

Alternatives
------------

What other ways could we do this thing? Why aren't we using those? This doesn't
have to be a full literature review, but it should demonstrate that thought has
been put into why the proposed solution is an appropriate one.

Data model impact
-----------------

No impact.

REST API impact
---------------

Each API method which is either added or changed should have the following

* Specification for the method

  * A description of what the method does suitable for use in
    user documentation

  * Method type (POST/PUT/GET/DELETE)

  * Normal http response code(s)

  * Expected error http response code(s)

    * A description for each possible error code should be included
      describing semantic errors which can cause it such as
      inconsistent parameters supplied to the method, or when an
      instance is not in an appropriate state for the request to
      succeed. Errors caused by syntactic problems covered by the JSON
      schema definition do not need to be included.

  * URL for the resource

  * Parameters which can be passed via the url

  * JSON schema definition for the body data if allowed

  * JSON schema definition for the response data if any

* Example use case including typical API samples for both data supplied
  by the caller and the response

* Discuss any policy changes, and discuss what things a deployer needs to
  think about when defining their policy.

Example JSON schema definitions can be found in the Nova tree
http://git.openstack.org/cgit/openstack/nova/tree/nova/api/openstack/compute/schemas/v3

Note that the schema should be defined as restrictively as
possible. Parameters which are required should be marked as such and
only under exceptional circumstances should additional parameters
which are not defined in the schema be permitted (eg
additionaProperties should be False).

Reuse of existing predefined parameter types such as regexps for
passwords and user defined names is highly encouraged.

Security impact
---------------

Describe any potential security impact on the system. Some of the items to
consider include:

* Does this change touch sensitive data such as tokens, keys, or user data?

* Does this change alter the API in a way that may impact security, such as
  a new way to access sensitive information or a new way to login?

* Does this change involve cryptography or hashing?

* Does this change require the use of sudo or any elevated privileges?

* Does this change involve using or parsing user-provided data? This could
  be directly at the API level or indirectly such as changes to a cache layer.

* Can this change enable a resource exhaustion attack, such as allowing a
  single API interaction to consume significant server resources? Some examples
  of this include launching subprocesses for each connection, or entity
  expansion attacks in XML.

For more detailed guidance, please see the OpenStack Security Guidelines as
a reference (https://wiki.openstack.org/wiki/Security/Guidelines). These
guidelines are a work in progress and are designed to help you identify
security best practices. For further information, feel free to reach out
to the OpenStack Security Group at <email address hidden>.

Notifications impact
--------------------
No impact.

There is no need for any use for the notification system.

Other end user impact
---------------------

Aside from the API, are there other ways a user will interact with this
feature?

* Does this change have an impact on python-novaclient? What does the user
  interface there look like?

Performance Impact
------------------

No impact.

Other deployer impact
---------------------

Discuss things that will affect how you deploy and configure OpenStack
that have not already been mentioned, such as:

* What config options are being added? Should they be more generic than
  proposed (for example a flag that other hypervisor drivers might want to
  implement as well)? Are the default values ones which will work well in
  real deployments?

* Is this a change that takes immediate effect after its merged, or is it
  something that has to be explicitly enabled?

* If this change is a new binary, how would it be deployed?

* Please state anything that those doing continuous deployment, or those
  upgrading from the previous release, need to be aware of. Also describe
  any plans to deprecate configuration values or features. For example, if we
  change the directory name that instances are stored in, how do we handle
  instance directories created before the change landed? Do we move them? Do
  we have a special case in the code? Do we assume that the operator will
  recreate all the instances in their cloud?

Developer impact
----------------

Discuss things that will affect other developers working on OpenStack,
such as:

* If the blueprint proposes a change to the driver API, discussion of how
  other hypervisors would implement the feature is required.

Implementation
==============

Assignee(s)
-----------

Who is leading the writing of the code? Or is this a blueprint where you're
throwing it out there to see who picks it up?

If more than one person is working on the implementation, please designate the
primary author and contact.

Primary assignee:
  <launchpad-id or None>

Other contributors:
  <launchpad-id or None>

Work Items
----------

Work items or tasks -- break the feature up into the things that need to be
done to implement it. Those parts might end up being done by different people,
but we're mostly trying to understand the timeline for implementation.

Dependencies
============

* Include specific references to specs and/or blueprints in nova, or in other
  projects, that this one either depends on or is related to.

* If this requires functionality of another project that is not currently used
  by Nova (such as the glance v2 API when we previously only required v1),
  document that fact.

* Does this feature require any new library dependencies or code otherwise not
  included in OpenStack? Or does it depend on a specific version of library?

Testing
=======

Please discuss the important scenarios needed to test here, as well as
specific edge cases we should be ensuring work correctly. For each
scenario please specify if this requires specialized hardware, a full
openstack environment, or can be simulated inside the Nova tree.

Please discuss how the change will be tested. We especially want to know what
tempest tests will be added. It is assumed that unit test coverage will be
added so that doesn't need to be mentioned explicitly, but discussion of why
you think unit tests are sufficient and we don't need to add more tempest
tests would need to be included.

Is this untestable in gate given current limitations (specific hardware /
software configurations available)? If so, are there mitigation plans (3rd
party testing, gate enhancements, etc).

Documentation Impact
====================

What is the impact on the docs team of this change? Some changes might require
donating resources to the docs team to have the documentation updated. Don't
repeat details discussed above, but please reference them here.

References
==========

Please add any useful references here. You are not required to have any
reference. Moreover, this specification should still make sense when your
references are unavailable. Examples of what you could include are:

* Links to mailing list or IRC discussions

* Links to notes from a summit session

* Links to relevant research, if appropriate

* Related specifications as appropriate (e.g. if it's an EC2 thing, link the
  EC2 docs)

* Anything else you feel it is worthwhile to refer to

History
=======

Optional section for liberty intended to be used each time the spec
is updated to describe new design, API or any database schema
updated. Useful to let reader understand what's happened along the
time.

.. list-table:: Revisions
   :header-rows: 1

   * - Release Name
     - Description
   * - Liberty
     - Introduced

Blueprint information

Status:
Not started
Approver:
None
Priority:
Undefined
Drafter:
Ahmed El-Khouly
Direction:
Needs approval
Assignee:
Ahmed El-Khouly
Definition:
New
Series goal:
None
Implementation:
Unknown
Milestone target:
None

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