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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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==========================================
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Example Spec - The title of your blueprint
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==========================================
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Include the URL of your launchpad blueprint:
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https://blueprints.launchpad.net/nova/+spec/example
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Introduction paragraph -- why are we doing anything? A single paragraph of
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prose that operators can understand. The title and this first paragraph
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should be used as the subject line and body of the commit message
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respectively.
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Some notes about the nova-spec and blueprint process:
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* Not all blueprints need a spec. For more information see
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https://docs.openstack.org/nova/latest/contributor/blueprints.html#specs
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* The aim of this document is first to define the problem we need to solve,
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and second agree the overall approach to solve that problem.
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* This is not intended to be extensive documentation for a new feature.
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For example, there is no need to specify the exact configuration changes,
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nor the exact details of any DB model changes. But you should still define
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that such changes are required, and be clear on how that will affect
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upgrades.
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* You should aim to get your spec approved before writing your code.
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While you are free to write prototypes and code before getting your spec
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approved, its possible that the outcome of the spec review process leads
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you towards a fundamentally different solution than you first envisaged.
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* But, API changes are held to a much higher level of scrutiny.
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As soon as an API change merges, we must assume it could be in production
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somewhere, and as such, we then need to support that API change forever.
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To avoid getting that wrong, we do want lots of details about API changes
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upfront.
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Some notes about using this template:
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* Your spec should be in ReSTructured text, like this template.
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* Please wrap text at 79 columns.
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* The filename in the git repository should match the launchpad URL, for
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example a URL of: https://blueprints.launchpad.net/nova/+spec/awesome-thing
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should be named awesome-thing.rst
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* Please do not delete any of the sections in this template. If you have
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nothing to say for a whole section, just write: None
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* For help with syntax, see http://sphinx-doc.org/rest.html
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* To test out your formatting, build the docs using tox and see the generated
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HTML file in doc/build/html/specs/<path_of_your_file>
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* If you would like to provide a diagram with your spec, ascii diagrams are
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required. http://asciiflow.com/ is a very nice tool to assist with making
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ascii diagrams. The reason for this is that the tool used to review specs is
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based purely on plain text. Plain text will allow review to proceed without
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having to look at additional files which can not be viewed in gerrit. It
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will also allow inline feedback on the diagram itself.
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* If your specification proposes any changes to the Nova REST API such
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as changing parameters which can be returned or accepted, or even
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the semantics of what happens when a client calls into the API, then
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you should add the APIImpact flag to the commit message. Specifications with
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the APIImpact flag can be found with the following query:
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https://review.openstack.org/#/q/status:open+project:openstack/nova-specs+message:apiimpact,n,z
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Problem description
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===================
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A detailed description of the problem. What problem is this blueprint
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addressing?
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Use Cases
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---------
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What use cases does this address? What impact on actors does this change have?
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Ensure you are clear about the actors in each use case: Developer, End User,
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Deployer etc.
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Proposed change
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===============
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Here is where you cover the change you propose to make in detail. How do you
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propose to solve this problem?
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If this is one part of a larger effort make it clear where this piece ends. In
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other words, what's the scope of this effort?
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At this point, if you would like to just get feedback on if the problem and
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proposed change fit in nova, you can stop here and post this for review to get
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preliminary feedback. If so please say:
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Posting to get preliminary feedback on the scope of this spec.
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Alternatives
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------------
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What other ways could we do this thing? Why aren't we using those? This doesn't
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have to be a full literature review, but it should demonstrate that thought has
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been put into why the proposed solution is an appropriate one.
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Data model impact
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-----------------
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Changes which require modifications to the data model often have a wider impact
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on the system. The community often has strong opinions on how the data model
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should be evolved, from both a functional and performance perspective. It is
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therefore important to capture and gain agreement as early as possible on any
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proposed changes to the data model.
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Questions which need to be addressed by this section include:
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* What new data objects and/or database schema changes is this going to
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require?
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* What database migrations will accompany this change.
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* How will the initial set of new data objects be generated, for example if you
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need to take into account existing instances, or modify other existing data
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describe how that will work.
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REST API impact
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---------------
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Each API method which is either added or changed should have the following
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* Specification for the method
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* A description of what the method does suitable for use in
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user documentation
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* Method type (POST/PUT/GET/DELETE)
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* Normal http response code(s)
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* Expected error http response code(s)
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* A description for each possible error code should be included
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describing semantic errors which can cause it such as
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inconsistent parameters supplied to the method, or when an
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instance is not in an appropriate state for the request to
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succeed. Errors caused by syntactic problems covered by the JSON
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schema definition do not need to be included.
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* URL for the resource
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* URL should not include underscores, and use hyphens instead.
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* Parameters which can be passed via the url
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* JSON schema definition for the request body data if allowed
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* Field names should use snake_case style, not CamelCase or MixedCase
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style.
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* JSON schema definition for the response body data if any
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* Field names should use snake_case style, not CamelCase or MixedCase
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style.
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* Example use case including typical API samples for both data supplied
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by the caller and the response
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* Discuss any policy changes, and discuss what things a deployer needs to
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think about when defining their policy.
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Example JSON schema definitions can be found in the Nova tree
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http://git.openstack.org/cgit/openstack/nova/tree/nova/api/openstack/compute/schemas
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Note that the schema should be defined as restrictively as
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possible. Parameters which are required should be marked as such and
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only under exceptional circumstances should additional parameters
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which are not defined in the schema be permitted (eg
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additionaProperties should be False).
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Reuse of existing predefined parameter types such as regexps for
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passwords and user defined names is highly encouraged.
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Security impact
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---------------
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Describe any potential security impact on the system. Some of the items to
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consider include:
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* Does this change touch sensitive data such as tokens, keys, or user data?
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* Does this change alter the API in a way that may impact security, such as
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a new way to access sensitive information or a new way to login?
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* Does this change involve cryptography or hashing?
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* Does this change require the use of sudo or any elevated privileges?
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* Does this change involve using or parsing user-provided data? This could
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be directly at the API level or indirectly such as changes to a cache layer.
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* Can this change enable a resource exhaustion attack, such as allowing a
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single API interaction to consume significant server resources? Some examples
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of this include launching subprocesses for each connection, or entity
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expansion attacks in XML.
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For more detailed guidance, please see the OpenStack Security Guidelines as
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a reference (https://wiki.openstack.org/wiki/Security/Guidelines). These
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guidelines are a work in progress and are designed to help you identify
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security best practices. For further information, feel free to reach out
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to the OpenStack Security Group at openstack-security@lists.openstack.org.
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Notifications impact
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--------------------
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Please specify any changes to notifications. Be that an extra notification,
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changes to an existing notification, or removing a notification.
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Consider proposing changes to the versioned notifications:
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* When the feature adds or removes fields to the API responses. For example
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when the feature adds a new field to the ``GET /servers`` API response
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consider adding similar information to the payload of the instance action
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notifications
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* When the feature adds a new action to the existing API entities. For example
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adding a new action to the server might mean you want to emit a corresponding
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new instance action notification
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* When the feature adds a new resource (noun) to the REST API consider adding
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new notifications about the creation and deletion of such resource
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Other end user impact
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---------------------
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Aside from the API, are there other ways a user will interact with this
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feature?
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* Does this change have an impact on python-novaclient? What does the user
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interface there look like?
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Performance Impact
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------------------
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Describe any potential performance impact on the system, for example
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how often will new code be called, and is there a major change to the calling
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pattern of existing code.
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Examples of things to consider here include:
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* A periodic task might look like a small addition but if it calls conductor or
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another service the load is multiplied by the number of nodes in the system.
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* Scheduler filters get called once per host for every instance being created,
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so any latency they introduce is linear with the size of the system.
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* A small change in a utility function or a commonly used decorator can have a
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large impacts on performance.
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* Calls which result in a database queries (whether direct or via conductor)
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can have a profound impact on performance when called in critical sections of
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the code.
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* Will the change include any locking, and if so what considerations are there
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on holding the lock?
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Other deployer impact
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---------------------
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Discuss things that will affect how you deploy and configure OpenStack
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that have not already been mentioned, such as:
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* What config options are being added? Should they be more generic than
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proposed (for example a flag that other hypervisor drivers might want to
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implement as well)? Are the default values ones which will work well in
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real deployments?
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* Is this a change that takes immediate effect after its merged, or is it
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something that has to be explicitly enabled?
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* If this change is a new binary, how would it be deployed?
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* Please state anything that those doing continuous deployment, or those
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upgrading from the previous release, need to be aware of. Also describe
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any plans to deprecate configuration values or features. For example, if we
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change the directory name that instances are stored in, how do we handle
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instance directories created before the change landed? Do we move them? Do
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we have a special case in the code? Do we assume that the operator will
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recreate all the instances in their cloud?
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Developer impact
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----------------
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Discuss things that will affect other developers working on OpenStack,
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such as:
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* If the blueprint proposes a change to the driver API, discussion of how
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other hypervisors would implement the feature is required.
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Upgrade impact
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--------------
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Describe any potential upgrade impact on the system, such as:
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* If this change adds a new feature to the compute host that the controller
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services rely on, the controller services may need to check the minimum
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compute service version in the deployment before using the new feature. For
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example, in Ocata, the FilterScheduler did not use the Placement API until
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all compute services were upgraded to at least Ocata.
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* While we strive to have feature parity between all virt drivers, it is not
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uncommon for one virt driver to implement a new feature exposed out of the
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API before the others. For example, extending the size of an attached
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volume. Since Nova does not yet have any type of sophisticated *capabilities*
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API so a user can know what actions can be performed on a given instance,
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consider adding a new policy rule to at least let operators that cannot
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support a virt-specific feature disable it in their cloud which is at least
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presented to the user in an understandable way by getting a ``403 Forbidden``
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error.
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* Nova supports N-1 version *nova-compute* services for rolling upgrades. Does
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the proposed change need to consider older code running that may impact how
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the new change functions, for example, by changing or overwriting global
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state in the database? This is generally most problematic when making changes
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that involve multiple compute hosts, like move operations such as migrate,
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resize, unshelve and evacuate.
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Implementation
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==============
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Assignee(s)
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-----------
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Who is leading the writing of the code? Or is this a blueprint where you're
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throwing it out there to see who picks it up?
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If more than one person is working on the implementation, please designate the
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primary author and contact.
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Primary assignee:
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<launchpad-id or None>
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Other contributors:
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<launchpad-id or None>
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Work Items
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----------
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Work items or tasks -- break the feature up into the things that need to be
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done to implement it. Those parts might end up being done by different people,
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but we're mostly trying to understand the timeline for implementation.
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Dependencies
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============
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* Include specific references to specs and/or blueprints in nova, or in other
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projects, that this one either depends on or is related to.
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* If this requires functionality of another project that is not currently used
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by Nova (such as the glance v2 API when we previously only required v1),
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document that fact.
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* Does this feature require any new library dependencies or code otherwise not
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included in OpenStack? Or does it depend on a specific version of library?
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Testing
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=======
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Please discuss the important scenarios needed to test here, as well as
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specific edge cases we should be ensuring work correctly. For each
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scenario please specify if this requires specialized hardware, a full
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openstack environment, or can be simulated inside the Nova tree.
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Please discuss how the change will be tested. We especially want to know what
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tempest tests will be added. It is assumed that unit test coverage will be
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added so that doesn't need to be mentioned explicitly, but discussion of why
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you think unit tests are sufficient and we don't need to add more tempest
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tests would need to be included.
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Is this untestable in gate given current limitations (specific hardware /
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software configurations available)? If so, are there mitigation plans (3rd
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party testing, gate enhancements, etc).
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Documentation Impact
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====================
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Which audiences are affected most by this change, and which documentation
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titles on docs.openstack.org should be updated because of this change? Don't
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repeat details discussed above, but reference them here in the context of
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documentation for multiple audiences. For example, the Operations Guide targets
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cloud operators, and the End User Guide would need to be updated if the change
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offers a new feature available through the CLI or dashboard. If a config option
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changes or is deprecated, note here that the documentation needs to be updated
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to reflect this specification's change.
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References
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==========
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Please add any useful references here. You are not required to have any
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reference. Moreover, this specification should still make sense when your
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references are unavailable. Examples of what you could include are:
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* Links to mailing list or IRC discussions
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* Links to notes from a summit session
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* Links to relevant research, if appropriate
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* Related specifications as appropriate (e.g. if it's an EC2 thing, link the
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EC2 docs)
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* Anything else you feel it is worthwhile to refer to
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History
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=======
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Optional section intended to be used each time the spec is updated to describe
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new design, API or any database schema updated. Useful to let reader understand
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what's happened along the time.
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.. list-table:: Revisions
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:header-rows: 1
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* - Release Name
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- Description
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* - Stein
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- Introduced
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