Generalized filtered listing on resources

Generalized filtered listing on resources

https://blueprints.launchpad.net/cinder/+spec/generalized-filtering-for-cinder-list-resource

Problem description

We continue adding various filter options to the Cinder List API’s. Things like “filter results by x=y”. This results in a good deal of code being added for one-off preferences or user convenience. It also means that we continue to bump micro-versions for such additions and create more versions of the API than we probably care to document, test and maintain.

What’s annoying about this is that it’s not even that we’re adding things to the server side, we’re instead just popping things off of the params in the request body based on what micro-version is specified.

The biggest area of churn for this sort of thing is in the client side of things.

Use Cases

Filters are convenient for operators doing things with large clouds. It’s certainly a nice-to-have feature to be able to do things like just ask Cinder for a list of all volumes with an error status, or that are bootable or the latest, suggestion all those that are attached to host xyz.

Proposed change

In order to add these today, we add a specific arg to the clients, and then we add specific arg parsing on the Cinder API server to interpret and parse these args. These parsed arguments are then just used to build a filter that we pass in to the sql call to get_volumes (or get_<resource>).

Rather than continuing to add these for the various resources in an ad-hoc manner, this spec proposes a generalized filtered-list mechanism. Rather than add a specific filter by name over and over, instead provide a single filter argument that supplies Key Value pairs to be used to build the db query filter. There’s likely some concern that people won’t know what valid filter keys are, for that we can also provide a list-filters command that could be used in an introspective sort of way, querying the object model for the valid filter items and returning it to the caller.

The list-filters component is derived from an Admin provided list of valid and enabled filters for end users to access. This obviously serves two purposes:

  1. Advertise what filters are enabled/available to the end user
  2. Gives the Cloud Operator the ability to pick what filters are enabled

It’s important to note that not all clouds will want to expose filters like backend-host and other internals that shouldn’t typically be leaked to the end user.

What’s interesting about this is from the API Servers perspective we don’t even really care about any of this. We can already pass in filters via the params in the request body and this just works. If you’re using curl this just works already as is. If you are using the client you’d just need a way to expose it properly: (https://gist.github.com/j-griffith/f455e51d3e597af96bfe7022974b5bd9)

Alternatives

  • We could certainly continue doing what we’re doing now and just adding specific filter arguments to the clients and the API, but I don’t think that’s sustainable.

  • We could provide a generalized “filters” (pick a better name) controller that could be called directly and then call the specified resource item with filters. This would mean you would do things like: cinder filters-list –resource volume to get a list of valid filter items for a volume (volumes should be the default).

    cinder filters-list –resource snapshot for snapshots, etc.

    But then have something like a cinder filtered-list –filter xyz=abc which would go to a filtered-list controller and then call the resource controller appropriately.

    This might be a good way to reduce some duplicate code and churn even further but it may require just as much work and code as just having each resource have it’s own “–filter” options to the list commands.

Data model impact

None

REST API impact

Other than adding the ability to view the valid filter keys we don’t even need to change anything on the Cinder server side currently.

Security impact

None that I’m aware of

Notifications impact

Other end user impact

Life would be better

Performance Impact

None

Other deployer impact

None

Developer impact

Life would be better

Implementation

Assignee(s)

Primary assignee:
john-griffith

Work Items

  • Add the filters arg to the client
  • Add the ability to query the API server for valid filters for a resource

Dependencies

Testing

Documentation Impact

We will need to update documentation to describe the new capability, although I expect anybody not using the client may already be exposing this on their own.

References

Creative Commons Attribution 3.0 License

Except where otherwise noted, this document is licensed under Creative Commons Attribution 3.0 License. See all OpenStack Legal Documents.

cinder-specs 0.0.1.dev432