[openstack-dev] a "common" client library

Alexei Kornienko alexei.kornienko at gmail.com
Thu Jan 16 17:07:03 UTC 2014

On 01/16/2014 06:15 PM, Jesse Noller wrote:
> On Jan 16, 2014, at 9:54 AM, Alexei Kornienko 
> <alexei.kornienko at gmail.com <mailto:alexei.kornienko at gmail.com>> wrote:
>> On 01/16/2014 05:25 PM, Jesse Noller wrote:
>>> On Jan 16, 2014, at 9:07 AM, Joe Gordon <joe.gordon0 at gmail.com 
>>> <mailto:joe.gordon0 at gmail.com>> wrote:
>>>> On Thu, Jan 16, 2014 at 9:45 AM, Jesse Noller 
>>>> <jesse.noller at rackspace.com <mailto:jesse.noller at rackspace.com>> wrote:
>>>>     On Jan 16, 2014, at 5:53 AM, Chmouel Boudjnah
>>>>     <chmouel at enovance.com <mailto:chmouel at enovance.com>> wrote:
>>>>>     On Thu, Jan 16, 2014 at 12:38 PM, Chris Jones <cmsj at tenshu.net
>>>>>     <mailto:cmsj at tenshu.net>> wrote:
>>>>>         Once a common library is in place, is there any intention
>>>>>         to (or resistance against) collapsing the clients into a
>>>>>         single project or even a single command (a la busybox)?
>>>>>     that's what openstackclient is here for
>>>>>     https://github.com/openstack/python-openstackclient
>>>>     After speaking with people working on OSC and looking at the
>>>>     code base in depth; I don't think this addresses what Chris is
>>>>     implying: OSC wraps the individual CLIs built by each project
>>>>     today, instead of the inverse: a common backend that the
>>>>     individual CLIs can wrap - the latter is an important
>>>>     distinction as currently, building a single binary install of
>>>>     OSC for say, Windows is difficult given the dependency tree
>>>>     incurred by each of the wrapped CLIs, difference in
>>>>     dependencies, structure, etc.
>>>>     Also, wrapping a series of inconsistent back end Client classes
>>>>     / functions / methods means that the layer that presents a
>>>>     consistent user interface (OSC) to the user is made more
>>>>     complex juggling names/renames/commands/etc.
>>>>     In the inverted case of what we have today (single backend); as
>>>>     a developer of user interfaces (CLIs, Applications, Web apps
>>>>     (horizon)) you would be able to:
>>>>     from openstack.common.api import Auth
>>>>     from openstack.common.api import Compute
>>>>     from openstack.common.util import cli_tools
>>>>     my_cli = cli_tools.build(...)
>>>>     def my_command(cli):
>>>>     compute = Compute(Auth(cli.tentant..., connect=True))
>>>>     compute.list_flavors()
>>>>     This would mean that *even if the individual clients needed or
>>>>     wanted to keep their specific CLIs, they would be able to use a
>>>>     not "least common denominator" back end (each service can have
>>>>     a rich common.api.compute.py <http://common.api.compute.py/> or
>>>>     api.compute/client.py and extend where needed. However tools
>>>>     like horizon / openstackclient can choose not to leverage the
>>>>     "power user/operator/admin" components and present a simplified
>>>>     user interface.
>>>>     I'm working on a wiki page + blueprint to brainstorm how we
>>>>     could accomplish this based off of what work is in flight today
>>>>     (see doug's linked blueprint) and sussing out a layout / API
>>>>     strawman for discussion.
>>>>     Some of the additions that came out of this email threads and
>>>>     others:
>>>>     1. Common backend should provide / offer caching utilities
>>>>     2. Auth retries need to be handled by the auth object, and each
>>>>     sub-project delegates to the auth object to manage that.
>>>>     3. Verified Mocks / Stubs / Fakes must be provided for proper
>>>>     unit testing
>>>> I am happy to see this work being done, there is definitely a lot 
>>>> of work to be done on the clients.
>>>> This blueprint sounds like its still being fleshed out, so I am 
>>>> wondering what the value is of the current patches 
>>>> https://review.openstack.org/#/q/topic:bp/common-client-library-2,n,z
>>>> Those patches mainly sync cliutils and apiutils from oslo into the 
>>>> assorted clients. But if this blueprint is about the python API and 
>>>> not the CLI (as that would be the openstack-pythonclient), why sync 
>>>> in apiutils?
>>>> Also does this need to go through oslo-incubator or can this start 
>>>> out as a library? Making this a library earlier on will reduce the 
>>>> number of patches needed to get 20+ repositories to use this.
>>> Alexei and others have at least started the first stage of a rollout 
>>> - the blueprint(s) needs additional work, planning and discussion, 
>>> but his work is a good first step (reduce the duplication of code) 
>>> although I am worried that the libraries and APIs / namespaces will 
>>> need to change if we continue these discussions which potentially 
>>> means re-doing work.
>>> If we take a step back, a rollout process might be:
>>> 1: Solidify the libraries / layout / naming conventions (blueprint)
>>> 2: Solidify the APIs exposed to consumers (blueprint)
>>> 3: Pick up on the common-client-library-2 work which is primarily a 
>>> migration of common code into oslo today, into the structure defined 
>>> by 1 & 2
>>> So, I sort of agree: moving / collapsing code now might be 
>>> premature. I do strongly agree it should stand on its own as a 
>>> library rather than an oslo incubator however. We should start with 
>>> a single, clean namespace / library rather than depending on oslo 
>>> directly.
>> Knowing usual openstack workflow I'm afraid that #1,#2 with a 
>> waterfall approach may take years to be complete.
>> And after they'll be approved it will become clear that this 
>> architecture is already outdated.
>> We try to use iterative approach for clients refactoring.
>> We started our work from removing code duplication because it already 
>> gives a direct positive effect on client projects.
>> If you can show us better way of moving forward please help us by 
>> uploading patches on this topic.
>> Talk is cheap. Show me the code. (c) Linus
> I don't disagree and I'm pretty sure I and others have already thanked 
> you for starting this but have expressed concerns about the API / 
> layout - and many of the patches on that blueprint are still pending 
> review due to those concerns. I'm not suggesting we need to spend the 
> next six years designing it, I'm arguing for some basic design. From 
> the current blueprint it is unclear where things will live, where it 
> will live and how does it benefit everyone.
> So I'd like to work *with* you to expand the blueprints to address 
> some basic design / namespacing / issues and not jump straight into 
> refactoring 22+ command line tools without a clear idea of the the 
> desired layout and design.
The problem with defining design is that I don't know a convenient way 
of doing it cause UML, etherpad, blueprint's description are not 
sufficient to do this clearly.
We try to use approach that I call "continuous refactoring" so as long 
as something can be improved we improve it.
Our basic goal is to move towards SOLID principles and as long every new 
commit brings us one step closer to them I consider that overall design 
is improving.
I've already posted here a draft idea of what we would like to see in 
the end:

> 1) Transport layer would handle all transport related stuff - HTTP, JSON
> encoding, auth, caching, etc.
> 2) Model layer (Resource classes, BaseManager, etc.) will handle data
> representation, validation
> 3) API layer will handle all project specific stuff - url mapping, etc.
> (This will be imported to use client in other applications)
> 4) Cli level will handle all stuff related to cli mapping - argparse,
> argcomplete, etc.

>>> jesse
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