Open Stack

​Hello,

I think the Mistral Project[1] aims the same goal, isn't it?

Regards,
jaume

[1]: https://wiki.openstack.org/wiki/Mistral


On 23 May 2014 09:28, Salvatore Orlando <sorlando at nicira.com> wrote:

> Nachi,
>
> I will be glad if the solution was as easy as sticking a task_state
> attribute to a resource! I'm afraid however that would be only the tip of
> the iceberg, or the icing of the cake, if you want.
> However, I agree with you that consistency across Openstack APIs is very
> important; whether this is a cross project discussion is instead debatable;
> my feeling here is that taskflow is the cross-project piece of the
> architecture, and every project then might have a different strategy for
> integrating it - as long as it does not result in inconsistent APIs exposed
> to customers!
>
> It is something that obviously will be considered when designing how to
> represent whether a DB resource is in sync with its actual configuration on
> the backend.
> I think this is something which might happen regardless of whether it will
> be also agreed to let API consumers access task execution information using
> the API.
>
> Salvatore
>
>
>
>
> On 23 May 2014 01:16, Nachi Ueno <nachi at ntti3.com> wrote:
>
>> Hi Salvatore
>>
>> Thank you for your posting this.
>>
>> IMO, this topic shouldn't be limited for Neutron only.
>> Users wants consistent API between OpenStack project, right?
>>
>> In Nova, a server has task_state, so Neutron should do same way.
>>
>>
>>
>> 2014-05-22 15:34 GMT-07:00 Salvatore Orlando <sorlando at nicira.com>:
>> > As most of you probably know already, this is one of the topics
>> discussed
>> > during the Juno summit [1].
>> > I would like to kick off the discussion in order to move towards a
>> concrete
>> > design.
>> >
>> > Preamble: Considering the meat that's already on the plate for Juno,
>> I'm not
>> > advocating that whatever comes out of this discussion should be put on
>> the
>> > Juno roadmap. However, preparation (or yak shaving) activities that
>> should
>> > be identified as pre-requisite might happen during the Juno time frame
>> > assuming that they won't interfere with other critical or high priority
>> > activities.
>> > This is also a very long post; the TL;DR summary is that I would like to
>> > explore task-oriented communication with the backend and how it should
>> be
>> > reflected in the API - gauging how the community feels about this, and
>> > collecting feedback regarding design, constructs, and related
>> > tools/techniques/technologies.
>> >
>> > At the summit a broad range of items were discussed during the session,
>> and
>> > most of them have been reported in the etherpad [1].
>> >
>> > First, I think it would be good to clarify whether we're advocating a
>> > task-based API, a workflow-oriented operation processing, or both.
>> >
>> > --> About a task-based API
>> >
>> > In a task-based API, most PUT/POST API operations would return tasks
>> rather
>> > than neutron resources, and users of the API will interact directly with
>> > tasks.
>> > I put an example in [2] to avoid cluttering this post with too much
>> text.
>> > As the API operation simply launches a task - the database state won't
>> be
>> > updated until the task is completed.
>> >
>> > Needless to say, this would be a radical change to Neutron's API; it
>> should
>> > be carefully evaluated and not considered for the v2 API.
>> > Even if it is easily recognisable that this approach has a few
>> benefits, I
>> > don't think this will improve usability of the API at all. Indeed this
>> will
>> > limit the ability of operating on a resource will a task is in
>> execution on
>> > it, and will also require neutron API users to change the paradigm the
>> use
>> > to interact with the API; for not mentioning the fact that it would look
>> > weird if neutron is the only API endpoint in Openstack operating in this
>> > way.
>> > For the Neutron API, I think that its operations should still be
>> > manipulating the database state, and possibly return immediately after
>> that
>> > (*) - a task, or to better say a workflow will then be started, executed
>> > asynchronously, and update the resource status on completion.
>> >
>> > --> On workflow-oriented operations
>> >
>> > The benefits of it when it comes to easily controlling operations and
>> > ensuring consistency in case of failures are obvious. For what is
>> worth, I
>> > have been experimenting introducing this kind of capability in the NSX
>> > plugin in the past few months. I've been using celery as a task queue,
>> and
>> > writing the task management code from scratch - only to realize that the
>> > same features I was implementing are already supported by taskflow.
>> >
>> > I think that all parts of Neutron API can greatly benefit from
>> introducing a
>> > flow-based approach.
>> > Some examples:
>> > - pre/post commit operations in the ML2 plugin can be orchestrated a lot
>> > better as a workflow, articulating operations on the various drivers in
>> a
>> > graph
>> > - operation spanning multiple plugins (eg: add router interface) could
>> be
>> > simplified using clearly defined tasks for the L2 and L3 parts
>> > - it would be finally possible to properly manage resources'
>> "operational
>> > status", as well as knowing whether the actual configuration of the
>> backend
>> > matches the database configuration
>> > - synchronous plugins might be converted into asynchronous thus
>> improving
>> > their API throughput
>> >
>> > Now, the caveats:
>> > - during the sessions it was correctly pointed out that special care is
>> > required with multiple producers (ie: api servers) as workflows should
>> be
>> > always executed in the correct order
>> > - it is probably be advisable to serialize workflows operating on the
>> same
>> > resource; this might lead to unexpected situations (potentially to
>> > deadlocks) with workflows operating on multiple resources
>> > - if the API is asynchronous, and multiple workflows might be queued or
>> in
>> > execution at a given time, rolling back the DB operation on failures is
>> > probably not advisable (it would not be advisable anyway in any
>> asynchronous
>> > framework). If the API instead stays synchronous the revert action for a
>> > failed task might also restore the db state for a resource; but I think
>> that
>> > keeping the API synchronous missed a bit the point of this whole work -
>> feel
>> > free to show your disagreement here!
>> > - some neutron workflows are actually initiated by agents; this is the
>> case,
>> > for instance, of the workflow for doing initial L2 and security group
>> > configuration for a port.
>> > - it's going to be a lot of work, and we need to devise a strategy to
>> either
>> > roll this changes in the existing plugins or just decide that future v3
>> > plugins will use it.
>> >
>> > From the implementation side, I've done a bit of research and task queue
>> > like celery only implement half of what is needed; conversely I have not
>> > been able to find a workflow manager, at least in the python world, as
>> > complete and suitable as taskflow.
>> > So my preference will be obviously to use it, and contribute to it
>> should we
>> > realize Neutron needs some changes to suit its needs. Growing something
>> > neutron-specific in tree is something I'd rule out.
>> >
>> > (*) This is a bit different from what many plugins do, as they execute
>> > requests synchronously and return only once the backend request is
>> > completed.
>> >
>> > --> Tasks and the API
>> >
>> > The etherpad [1] contains a lot of interesting notes on this topic.
>> > One important item it to understand how tasks affect the resource's
>> status
>> > to indicate their completion or failure. So far Neutron resource status
>> > pretty much expresses its "fabric" status. For instance a port is "UP"
>> if
>> > it's been wired by the OVS agent; it often does not tell us whether the
>> > actual resource configuration is exactly the desired one in the
>> database.
>> > For instance, if the ovs agent fails to apply security groups to a
>> port, the
>> > port stays "ACTIVE" and the user might never know there was an error
>> and the
>> > actual state diverged from the desired one.
>> >
>> > It is therefore important to allow users to know whether the backend
>> state
>> > is in sync with the db; tools like taskflow will be really helpful to
>> this
>> > aim.
>> > However, how should this be represented? The main options are to either
>> have
>> > a new attribute describing the resource sync state, or to extend the
>> > semantics of the current status attribute to include also resource sync
>> > state. I've put some rumblings on the subjects in the etherpad [3].
>> > Still, it has been correctly pointed out that it might not be enough to
>> know
>> > that a resource is out of sync, but it is good to know which operation
>> > exactly failed; this is where exposing somehow tasks through the API
>> might
>> > come handy.
>> >
>> > For instance one could do something like:
>> >
>> > GET /tasks?resource_id=<res_id>&task_state=FAILED
>> >
>> > to get failure details for a given resource.
>> >
>> > --> How to proceed
>> >
>> > This is where I really don't know... and I will therefore be brief.
>> > We'll probably need some more brainstorming to flush out all the
>> details.
>> > Once that is done, it might the case of evaluating what needs to be
>> done and
>> > whether it is better to target this work onto existing plugins, or
>> moving it
>> > out to v3 plugins (and hence do the actual work once the "core
>> refactoring"
>> > activities are complete).
>> >
>> > Regards,
>> > Salvatore
>> >
>> >
>> > [1] https://etherpad.openstack.org/p/integrating-task-into-neutron
>> > [2] http://paste.openstack.org/show/81184/
>> > [3] https://etherpad.openstack.org/p/sillythings
>> >
>> >
>> >
>> >
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>> >
>>
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-- 
Jaume Devesa
Software Engineer at Midokura
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