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26 июня 2015 г. 2:47 пользователь "GHANSHYAM MANN" <ghanshyammann at gmail.com>
написал:
>
> On Sat, Jun 20, 2015 at 9:14 AM, Devananda van der Veen
> <devananda.vdv at gmail.com> wrote:
> > Almost all of our discussions so far on this topic have left something
out,
> > which Monty pointed out to me last week. I'm following up now because
> > E_TRAVEL...
> >
> > tldr;
> > What we're versioning here are API's, not packages. It's not a question
of
> > numbering and dependency ordering, but of communicating support[ed|able]
> > interfaces between running services. Libtool is more relevant than
semver.
> >
> >
http://www.gnu.org/software/libtool/manual/html_node/Updating-version-info.html
> >
> > Right now we lack a means to express that the API response is
> > "compatible-with" a particular previously-released version of the API.
If we
> > had that, instead of "current-version", I believe we would have much
happier
> > users (and a happier Dmitry and jroll).
> >
> >
> > Long version...
> > Every HTTP response from Ironic today includes three headers: min, max,
and
> > version. The service can present an older API version, as long as it is
> > greater-than-or-equal-to the minimum supported version, even if that
version
> > is incompatible with the maximum supported version.  It does this by
> > rewriting responses to match what was expected in the requested (older)
> > version.
> >
> > When the newer version is identical *for all interfaces present* in the
> > older version, this can be called compatible. Dmitry's point is that we
> > don't need to hide newer interfaces from users who request an older API
> > version, because the client won't know or care about things that
weren't in
> > the version it requested.
> >
> > However, we *do* need to signal their presence, and we don't have a good
> > means for that right now. We also need to signal to the client that the
> > response given is "compatible with" a certain "age" of API, even if
it's not
> > exactly the same. And we don't have any means for that, either.
> >
> > Time for an example....
> >
> > Let's say that an incompatible change was made in v1.3. Let's also say
that
> > a change was made in v1.5 that added a new endpoint. Today, this is
what the
> > response headers would look like when calling a server running v1.5.
> >
> > a) client requests v1.2, receives headers (min: 1.1, max: 1.5, current:
1.2)
> > b) client requests v1.4, receives headers (min: 1.1, max: 1.5, current
1.4)
> > c) client requests v1.5, receives headers (min: 1.1, max: 1.5, current:
1.5)
> >
> > What we have implemented today is that in case (b), the service will
*hide*
> > any changes that we introduced in v1.5. But those changes did not
affect any
> > functionality of the v1.4 API, so Dmitry objects to this. So do I.
> >
> > The issue at hand is the response in case (b) ... though after spending
the
> > last several months working on api versioning, I actually think all of
those
> > are poor responses.
> >
> > What I believe we should have:
> > a) client requests v1.2, receives headers (min: 1.1, max: 1.5,
> > compatible-with: 1.1)
> > b) client requests v1.4, receives headers  (min: 1.1, max: 1.5,
> > compatible-with: 1.3)
> > b) client requests v1.5, receives headers  (min: 1.1, max: 1.5,
> > compatible-with: 1.3)
> >
>
> This is nice idea to return "compatible-with" information. But I feel
> each microversion either backward compatible or not should have their
> unique output only for what they had been introduced (not include new
> version changes).

Sigh. Please provide some justification.

>
> If older version shows what is in newer version(backward comp) then,
> there is no meaning
> of introducing those compatible changes as microversion. And if so
> then it blank out whole
> idea of publishing changes/features through microversion even they are
> backward compatible.

The main reason for versioning is feature discovery. It had nothing to do
with feature hiding. Please read the whole thread to see why feature hiding
is actually harmful.

>
> How about combining those means older version do not include anything
> from newer version
> but it returns "compatible-with:" information also which can be useful
> for user to bump version easily.
>
> > Yes -- (b) and (c) are identical responses.
> >
> > Discuss.
> >
> > -Devananda
> >
> >
> > On Tue, Jun 16, 2015 at 7:13 AM Dmitry Tantsur <dtantsur at redhat.com>
wrote:
> >>
> >> On 06/16/2015 03:47 PM, Jim Rollenhagen wrote:
> >> > On Tue, Jun 16, 2015 at 08:56:37AM +0200, Dmitry Tantsur wrote:
> >> >> On 06/04/2015 08:58 AM, Xu, Hejie wrote:
> >> >>> Hi, guys,
> >> >>> I’m working on adding Microversion into the API-WG’s guideline
which
> >> >>> make sure we have consistent Microversion behavior in the API for
> >> >>> user.
> >> >>> The Nova and Ironic already have Microversion implementation, and
as I
> >> >>> know Magnum _https://review.openstack.org/#/c/184975/_ is going to
> >> >>> implement Microversion also.
> >> >>> Hope all the projects which support( or plan to) Microversion can
join
> >> >>> the review of guideline.
> >> >>> The Mircoversion specification(this almost copy from nova-specs):
> >> >>> _https://review.openstack.org/#/c/187112_
> >> >>> And another guideline for when we should bump Mircoversion
> >> >>> _https://review.openstack.org/#/c/187896/_
> >> >>> As I know, there already have a little different between Nova and
> >> >>> Ironic’s implementation. Ironic return min/max version when the
> >> >>> requested
> >> >>> version doesn’t support in server by http-headers. There isn’t such
> >> >>> thing in nova. But that is something for version negotiation we
need
> >> >>> for
> >> >>> nova also.
> >> >>> Sean have pointed out we should use response body instead of http
> >> >>> headers, the body can includes error message. Really hope ironic
team
> >> >>> can take a
> >> >>> look at if you guys have compelling reason for using http headers.
> >> >>> And if we think return body instead of http headers, we probably
need
> >> >>> think about back-compatible also. Because Microversion itself isn’t
> >> >>> versioned.
> >> >>> So I think we should keep those header for a while, does make
sense?
> >> >>> Hope we have good guideline for Microversion, because we only can
> >> >>> change
> >> >>> Mircoversion itself by back-compatible way.
> >> >>> Thanks
> >> >>> Alex Xu
> >> >>
> >> >> Hi all!
> >> >>
> >> >> I'd like to try put in feedback based on living with microversions
in
> >> >> Kilo
> >> >> release of Ironic.
> >> >
> >> > And here's my take, based on my experiences. Keep in mind I'm a core
> >> > reviewer, a developer, and an operator of Ironic.
> >>
> >> Thanks Jim, much appreciated!
> >>
> >> >
> >> >  From an ops perspective, our team has built our fair share of
tooling
> >> > to
> >> > help us run Ironic. Some of it uses the REST API via python or
node.js,
> >> > and of course we all use the CLI client often.
> >> >
> >> > We also continuously deploy Ironic, for full transparency. My
experience
> >> > is not with how this works every 6 months, but in the day-to-day.
> >> >
> >> >>
> >> >> First of all, after talking to folks off-list, I realized that we
all,
> >> >> and
> >> >> the spec itself, confuse 3 aspects of microversion usage:
> >> >>
> >> >> 1. protecting from breaking changes.
> >> >> This is clearly a big win from user's point of view, and it allowed
us
> >> >> to
> >> >> conduct painful change with renaming an important node state in our
> >> >> state
> >> >> machine. It will allows us even worse change this cycle: change of
the
> >> >> default state.
> >> >>
> >> >
> >> > +1. Good stuff. My tooling doesn't break when I upgrade. Yay.
> >> >
> >> >> 2. API discoverability.
> >> >> While I believe that there maybe be better implementation of this
idea,
> >> >> I
> >> >> think I got it now. People want services to report API versions they
> >> >> support. People want to be able to request a specific version, and
fail
> >> >> early if it is not present. Also +1 from me.
> >> >>
> >> >
> >> > I don't tend to personally do this. I usually am aware of what
version
> >> > of Ironic I'm running against. However I see how this could be useful
> >> > for other folks.
> >> >
> >> > I do, however, use the versions to say, "Oh, I can now request 1.5
which
> >> > has logical names! That's useful, let's set those to the names in our
> >> > CMDB." Now my tooling that interacts with the CMDB and Ironic can
look
> >> > at the version and decide to use node.name instead of the old hack we
> >> > used to use.
> >> >
> >> >> 3. hiding new features from older clients
> >> >> This is not directly stated by the spec, but many people imply it,
and
> >> >> Nova
> >> >> and Ironic did it in Kilo. I want us to be clear: it is not the
same as
> >> >> #2.
> >> >> You can report versions, but still allow new features to be used.
> >> >>
> >> >
> >> > This is still totally useful. If you know what version you are
running
> >> > against, you know exactly what features are available.
> >>
> >> "You know" is about #2 - that's where confusion is :)
> >> so if you know, that moving to inspection state is disallowed for your
> >> tooling (but not for the whole system!), what does it give you?
> >>
> >>
> >>
> >> >
> >> > I think the disconnect here is that we don't expect users (whether
those
> >> > are people or computers) to explicitly request a version. We need to
> >> > message better that if you are using Ironic or building a tool
against
> >> > Ironic's API, you should be pinning the version. We also need to take
> >> > this comment block[0] and put it in our docs, so users know what each
> >> > version does.
> >> >
> >> > Knowing that I get feature X when I upgrade to version Y is useful.
> >> >
> >> >> It is this particular thing that gets -2 from me, after I've seen
how
> >> >> it
> >> >> worked in practice, and that's why.
> >> >>
> >> >> First of all, I don't believe anyone needs it. Seriously, I can't
> >> >> imagine a
> >> >> user asking "please prevent me from using non-breaking changes". And
> >> >> attempt
> >> >> to implement it was IMO a big failure for the following reasons:
> >> >>
> >> >> a) It's hard to do. Even we, the core team, got confused, and for
> >> >> non-core
> >> >> people it took several iteration to do right. It's a big load on
both
> >> >> developers and reviewers.
> >> >>
> >> >
> >> > I do agree with this. It's been painful. However, I think we're
mostly
> >> > past that pain at this point. Does this patch[1] look like developer
> >> > pain?
> >>
> >> It's not that painful to write. Now. When we have 10-20 version, it
> >> probably will :)
> >> anyway, it's hard to explain newcomers how to do it, and it's hard to
> >> review the result. we failed at it, e.g. with error codes.
> >>
> >> >
> >> >> b) It's incomplete (at least for Ironic). We have several
API-exposed
> >> >> things
> >> >> that are just impossible to hide. Good example are node states: if
node
> >> >> is
> >> >> in a new state, we can't but expose it to older tooling. Our
free-form
> >> >> JSON
> >> >> fields properties, instance_info, driver_info and
driver_internal_info
> >> >> are
> >> >> examples as well. It's useless to speak about API contract, while we
> >> >> have
> >> >> those.
> >> >>
> >> >
> >> > I somewhat agree here.
> >> >
> >> > With node states, there are cases where we were able to hide it
> >> > (NOSTATE -> AVAILABLE), and cases where we were not (adding
MANAGEABLE).
> >> > However, this list of states is (AIUI) not part of the API contract;
> >> > rather the verbs available to move between states are.
> >>
> >> What's the point in contract, if there are things not covered by it
that
> >> drastically change the system behavior?
> >>
> >> >
> >> > As far as JSON fields, we've never had a contract around what keys
are
> >> > available. Only the semantics of working with those fields, and which
> >> > fields exist.
> >>
> >> ditto as above: you can request new features by modifying driver_info.
> >>
> >> >
> >> >> c) It gives additional push back to making (required) breaking
changes.
> >> >> We
> >> >> already got suggestions to have ONE MORE feature gating for breaking
> >> >> changes. Reason: people will need to increase microversions to get
> >> >> features,
> >> >> and your breaking change will prevent it.
> >> >>
> >> >
> >> > This is just silly. If 1.10 breaks a user, and the user wants 1.11,
> >> > they'll need to fix that breakage.
> >>
> >> ++ but not everyone agreed on the summit, when I was talking about
> >> ENROLL state
> >>
> >> >
> >> >> d) It requires a hard compromise on the CLI tool. You either
default it
> >> >> to
> >> >> 1.0 forever, and force all the people to get used to figuring out
> >> >> version
> >> >> numbers and using `ironic --ironic-api-version x.y` every time
> >> >> (terrible
> >> >> user experience), or you default it to some known good version,
bumping
> >> >> it
> >> >> from time to time. This, in turn, has 2 more serious problems:
> >> >>
> >> >
> >> > I disagree that pinning a version all the time is a terrible
experience.
> >> > We already require a number of options for authentication
(OS_USERNAME,
> >> > OS_PASSWORD, etc etc). How many folks do you think type these in
every
> >> > time? Solution is simple: add IRONIC_API_VERSION to whatever exports
the
> >> > other environment variables.
> >>
> >> It's not that bad, especially if devstack/tripleo will provide some
> >> reasonable default for you.
> >>
> >> I remember, however, Devananda didn't like the idea.
> >>
> >> And it definitely makes a quick start guide a bit harder to follow. I
> >> already imagine how many people will forget about this pinning (either
> >> to do it, or do update when they need new features).
> >>
> >> >
> >> > The version depends on the environment you are running against - why
not
> >> > treat it as such?
> >> >
> >> >> d.1) you start to break people \o/ that's not a theoretical concern:
> >> >> our
> >> >> downstream tooling did get broken by updating to newer ironicclient
> >> >> from git
> >> >>
> >> >
> >> > As I said before, we need to encourage folks to pin client versions
if
> >> > they don't want to break. I'm probably alone here, but I would even
> >> > propose making the version *required*. Force people to think about
what
> >> > they are doing. If folks are okay with being broken, they can pass
> >> > "latest".
> >>
> >> Could be a good default for devstack btw
> >>
> >> >
> >> >> d.2) you require complex version negotiations on the client side.
> >> >> Otherwise
> >> >> imaging CLI tool defaulting to 1.6 will issue `node-create` to
Ironic
> >> >> supporting only 1.5. Guess what? It will fail despite node-create
being
> >> >> very
> >> >> old feature. Again, that's not something theoretical: that's how we
> >> >> broke
> >> >> TripleO CI.
> >> >>
> >> >
> >> > Again, pin it.
> >> >
> >> >> e) Every microversion should be fully tested separately. Which
ended up
> >> >> in
> >> >> Ironic having 4 versions 1.2-1.5 that were never ever gate tested.
Even
> >> >> worse, initially, our gate tested only the oldest version 1.1, but
we
> >> >> solved
> >> >> it (though it took time to realize). The only good thing here is
that
> >> >> these
> >> >> versions 1.2-1.5 were probably never used by anyone.
> >> >>
> >> >
> >> > Hi. I've used some of these. :)
> >>
> >> You didn't tell me last time we talked :) note, that you didn't use
> >> them, unless you explicitly requested, because IIRC we never defaulted
> >> our client to any of these. So for most people, even deploying from
> >> master, it was 1.1 -> 1.6.
> >>
> >> >
> >> > // jim
> >> >
> >> > [0]
> >> >
https://github.com/openstack/ironic/blob/master/ironic/api/controllers/v1/__init__.py#L59-63
> >> > [1]
> >> >
https://review.openstack.org/#/c/188873/1/ironic/api/controllers/v1/node.py
> >> >>
> >> >> To sum this long post up, I'm seeing that hiding new features based
on
> >> >> microversions brings much more problems, than it solves (I'm not
aware
> >> >> of
> >> >> the latter at all). I'm very opposed to continuing doing it in
Ironic,
> >> >> and
> >> >> I'm going to propose patch stopping gating Kilo changes
(non-breaking
> >> >> obviously).
> >> >>
> >> >> Hope that helps,
> >> >> Dmitry
> >> >>
> >> >>>
> >
> >
> >
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>
>
>
> --
> Thanks & Regards
> Ghanshyam Mann
>
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