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Hi Przemek,

Thanks for detailed description of the issues you faced.

+1 for this approach, let's keep pure-UI implementation for 6.1 - it will
work for 99% of the cases.


2015-02-26 21:35 GMT+07:00 Przemyslaw Kaminski <pkaminski at mirantis.com>:

> Hello,
>
> Recently I've been asked to implement Python side of a simple feature:
> before deployment tell the UI user that network verification for current
> cluster configuration has not been performed. Moreover, on the UI side
> it's possible to do network checking on usaved cluster data -- in that
> case treat is as no network checking was performed. Unfortunately it
> turned out to be not at all that simple to implement on the backend and
> I'll try to explain why.
>
> I ended up with the implementation [1] that added a tri-valued flag to
> the Cluster model. What's surprising I got stuck at the idempotency test
> of network configuration: I've sent a GET request on network config,
> then sent a PUT with the received data and asserted that nothing
> changed. What's strange in about 1/4 cases this test failed because some
> ips got assigned differently. I wasn't able to explain why (I had other
> tasks to do and this one was somewhat of a side-project). BTW, it turned
> out that we have at least 2 functions that are used to deeply compare 2
> objects, both unnecessary IMHO as there are 3rd party libs for this,
> like [3].
>
> Another issue was that network configuration PUT returns a task while
> actually there is no asynchronicity there at all, it's just a huge
> validator that executes everything synchronously. This was already
> heavily commented in [2] and it's proposed to remove that task
> completely. Moreover Nova and Neutron backends returned different
> statuses albeit their verification code was almost the same. A
> unification of these 2 handlers was proposed in [1].
>
> Another issue is that we have to somehow invalidate the flag that says
> cluster verification is done. It is not difficult to overwrite the save
> method for Cluster so that any change in cluster invalidates network
> checking. But it's not that simple. First of all -- not all cluster's
> changes should invalidate the network checking. Second -- not only
> cluster changes invalidate that -- adding nodes to cluster, for example,
> invalidates network checking too. Adding triggers all over the code that
> check this don't seem to be a good solution.
>
> So what I proposed is to instead of having a simple flag like in [1] to
> actually store the whole JSON object with serialized network
> configuration. The UI, upon deployment, will ask the API about cluster
> and there we will return an additional key called 'network_status_check'
> that is 'failed', 'passed' or 'not_performed'. The API will determine
> that flag by getting that saved JSON object and comparing it with a
> freshly serialized object. This way we don't need to alter the flag upon
> save or anything, we just compute if it was changed on demand.
>
> I guess this change grew out so big that it requires a blueprint and can
> be done for 7.0. The feature can be implemented on the UI side only that
> covers most (but not all of) the problems and is "good enough" for 6.1.
>
> [1] https://review.openstack.org/153556
> [2]
>
> https://review.openstack.org/#/c/137642/15/nailgun/nailgun/api/v1/handlers/network_configuration.py
> [3] https://github.com/inveniosoftware/dictdiffer
>
> P.
>
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-- 
Vitaly Kramskikh,
Fuel UI Tech Lead,
Mirantis, Inc.
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