ironic-specs/specs/template.rst

Title of the Spec - eg the title of your blueprint

Include the URL of your launchpad blueprint:

https://blueprints.launchpad.net/ironic/+spec/template

Introduction paragraph -- start here.

Why are we doing anything? This should be a single paragraph of prose that operators can understand.

Some notes about using this template:

• Your spec should be in ReSTructured text, like this template.

• Please wrap text at 79 columns.

• The filename in the git repository must match the launchpad URL, for example a URL of: https://blueprints.launchpad.net/ironic/+spec/awesome-thing must be named awesome-thing.rst

• Please do not delete any of the sections in this template. If you have nothing to say for a whole section, just write: None

• For help with syntax, see http://sphinx-doc.org/rest.html

• To test out your formatting, build the docs using tox, or see: http://rst.ninjs.org

• If you would like to provide a diagram with your spec, ascii diagrams are required. http://asciiflow.com/ is a very nice tool to assist with making ascii diagrams. The reason for this is that the tool used to review specs is based purely on plain text. Plain text will allow review to proceed without having to look at additional files which can not be viewed in gerrit. It will also allow inline feedback on the diagram itself.

• If your specification proposes any changes to the Ironic REST API such as changing parameters which can be returned or accepted, or even the semantics of what happens when a client calls into the API, then you should add the APIImpact flag to the commit message. Specifications with the APIImpact flag can be found with the following query:

  https://review.openstack.org/#/q/status:open+project:openstack/ironic-specs+message:apiimpact,n,z

• If you are unsure whether this proposal is aligned with the project's mission and scope, you are encouraged to submit a minimal spec to get feedback early, before investing the effort in a complete specification. Do this by filling in the Problem description and Proposed change sections and delete the rest of the template. This will fail unit tests, but will still get attention from the review team.

• If you do not wish to submit a complete spec (for example, you do not plan to complete the spec during this cycle but would like to document the idea) you can submit a short spec. It must contain at least the Problem description and Proposed change sections, and may optionally contain any other valid sections. Propose this to the specs/backlog directory. This must follow all other rules of a regular spec (eg, it still requires a blueprint, good RST formatting, etc).

Problem description

A detailed description of the problem:

• For a new feature this might be use cases. Ensure you are clear about the actors in each use case: End User, Admin User, Deployer, or another Service
• For a major reworking of something existing it would describe the problems in that feature that are being addressed.

Proposed change

Here is where you cover the change you propose to make in detail. How do you propose to solve this problem?

If this is one part of a larger effort make it clear where this piece ends. In other words, what is the scope of this effort?

If you are unsure whether this proposal is aligned with the project's mission and scope, stop here.

Alternatives

What other ways could we do this thing? Has someone else done this thing in another project? In another language? 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

Changes which require modifications to the data model often have a wider impact on the system. The community often has strong opinions on how the data model should be evolved, from both a functional and performance perspective. It is therefore important to capture and gain agreement as early as possible on any proposed changes to the data model.

Questions which need to be addressed by this section include:

• What new data objects and/or database schema changes is this going to require?
• What database migrations will accompany this change?
• How will the initial set of new data objects be generated? For example, if you need to take into account existing instances, or modify other existing data, describe how that will work.

State Machine Impact

Interaction between the proposed change and the Ironic state machine should be documented here.

Questions which need to be addressed by this section include:

• Are you adding or removing any states or verbs?
• Are you changing any state transitions?
• What states are impacted by this change? This includes situations where an additional action is being performed on nodes in a given state.

Any change to the state machine is also a REST API change, and should also be documented accordingly in the next section.

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/PATCH)
  • Normal http response code(s)
  • Expected error http response code(s)
    • A description for each possible error code should be included. Describe semantic errors which can cause it, such as inconsistent parameters supplied to the method, or when a resource 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, including data types
  • JSON schema definition for the body data if allowed
  • JSON schema definition for the response data if any
• Does the API microversion need to increment?
• 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.
• Is a corresponding change in the client library and CLI necessary?
• Is this change discoverable by clients? Not all clients will upgrade at the same time, so this change must work with older clients without breaking them.

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.

Use of free-form JSON dicts should only be permitted where necessary to allow divergence in the drivers. In such case, the drivers must expose the expected content of the JSON dict and an ability to validate it.

Reuse of existing predefined parameter types is highly encouraged.

Client (CLI) impact

Typically, but not always, if there are any REST API changes, there are corresponding changes to python-ironicclient. If so, what does the user interface look like. If not, describe why there are REST API changes but no changes to the client.

RPC API impact

Changes which affect the RPC API should be listed here. For example:

• What are the changes, if any, to existing API calls?
• What new API calls are being added? Will these be using cast() or call()?
• ironic-api and ironic-conductor services must be upgradable independently. What is the upgrade process for rolling this change out to an existing deployment?

Driver API impact

Changes which affect the driver API have a direct effect on all drivers, and often have a wider impact on the system. There are several things to consider in this section.

• Is it a change to a "core" or "common" API?
• Can all drivers support it initially, or is it specific to a particular vendor's hardware?
• How will it be tested in the gate and in third-party CI systems?
• If adding a new interface, explain the intended scope of the proposed interface, what functionality it enables, why it is needed, and whether it is supported by current drivers.
• If adding or changing a method on an existing interface, the impact on existing drivers should be explored.
• Will the new interface or method need to be invoked when the hash ring rebalances, for example to rebuild local state on a new conductor service?
• How does this affect upgrades? Third-party drivers could be updated independently from this change, and care must be taken not to break backwards-compatibility within our Driver API.

Nova driver impact

Chances are, if this change affects the REST or Driver APIs, it will also affect the Nova driver in some way. If this requires a functional change in Nova, chances are the Nova team will require a spec to discuss the changes to their project as well. Provide a link to that here, or a justification for why that is not needed.

Questions which need to be addressed in this section include:

• What is the impact on Nova?
• If this change is enabling new functionality exposed via Nova, this section should cite the relevant components within other Nova drivers that already implement this.
• Ironic and Nova services must be upgradable independently. If the change affects existing functionality of the nova.virt.ironic driver, how will an upgrade be performed? How will it be tested?

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 credentials?
• Does this change affect the accessibility of hardware managed by Ironic?
• 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 openstack-security@lists.openstack.org.

Other end user impact

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

• Will this require changes in the Horizon panel, or any other OpenStack project?

Scalability impact

Describe any potential scalability impact on the system, for example any increase in network, RPC, or database traffic, or whether the feature requires synchronization across multiple services.

Examples of things to consider here include:

• Additional network calls to internal or external services.
• Additional disk or network traffic that will be required by the feature.
• Any change in the number of physical nodes which can be managed by each conductor service.

Performance Impact

Describe any potential performance impact on the system, for example how often will new code be called, and is there a major change to the calling pattern of existing code.

Examples of things to consider here include:

• A periodic task might look like a small addition, but all periodic tasks run in a single thread so a periodic task that takes a long time to run will have an effect on the timing of other periodic tasks.
• A small change in a utility function or a commonly used decorator can have a large impact on performance.
• Calls which result in one or more database queries (whether in the api or conductor services) can have a profound impact on performance when called in critical sections of the code.
• Will the change include any TaskManager locking, and if so what considerations are there on holding the lock?
• How will the new code be affected if the hash ring rebalances while it is running?

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 hardware drivers might want to implement as well)? Are the default values appropriate for production? Provide an explanation of why these defaults are reasonable.
• Is this a change that takes immediate effect after it's merged, or is it something that has to be explicitly enabled?
• If this change adds a new service that deployers will be required to run, how would it be deployed? Describe the expected topology, for example, what network connectivity the new service would need, what service(s) it would interact with, how many should run relative to the size of the deployment, and so on.
• 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 were to change the directory that PXE boot files were stored in, how would we update existing boot files created before the change landed? Would we require deployers to manually move them? Is there a special case in the code, which would be removed after some deprecation period? Would we require operators to delete and recreate all instances in order to perform the upgrade?

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 drivers 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 Ironic, 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 Ironic, 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?
• Does this feature target specific hardware? If so, is it a common standard (eg IPMI) or a vendor-specific implementation (eg iLO)?

Testing

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)?

Upgrades and Backwards Compatibility

Care must be taken to support our users by not breaking backwards compatibility with either REST API or Driver API changes.

• If your proposal includes any changes to the REST API, describe how existing clients will continue to function when interacting with an upgraded API server.
• If your proposal includes any changes to the Driver API, describe how existing driver implementations will continue to function when loaded by a conductor running with the new driver base class.
• Describe what testing you will be adding to ensure that backwards compatibility is maintained.
• If deprecating an existing feature or API, describe the deprecation plan, and for how long compatibility will be maintained.

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