I'm tempted to consider such HTTP headers modification as a feature as
per the Nova policy about bugs vs. features, hence the Wishlist

I also wonder if it would be better to rather create a blueprint in
https://blueprints.launchpad.net/nova/ and add a new spec if it needs an
API microversion.

Given it's possibly something the API SIG would be discussed before
Nova, let's invalid now for Nova that bug report, and ask to create the
Nova blueprint only after the API SIG discussed that and has a

** Changed in: nova
       Status: New => Confirmed

** Changed in: nova
   Importance: Undecided => Wishlist

** Changed in: nova
       Status: Confirmed => Incomplete

** Changed in: nova
       Status: Incomplete => Invalid

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  Openstack APIs and RFC 7234 HTTP caching

Status in OpenStack Compute (nova):
Status in openstack-api-sig:

Bug description:
  I recently hit an issue where I was using Terraform through an HTTP proxy 
(enforced by my company IT) to provision some resources in an Openstack cloud. 
Since creating the resources took some time, the initial response from 
openstack was "still creating...". Further polling of the resource status 
resulted in receiving *cached* copies of "still creating..." from the proxy 
until time-out.

  RFC7234 that describes HTTP caching states that in absence of all
  headers describing the lifetime/validity of the response, heuristic
  algorithms may be applied by caches to guesstimate an appropriate
  value for the validity of the response... (Who knows what is
  implemented out there...) See: the HTTP caching RFC section 4.2.2

  The API responses describe the current state of an object which isn't
  permanent, but has a limited validity. In fact very limited as the
  state of an object might change any moment.

  Therefore it is my opinion that the Openstack API (Nova in this case,
  but equally valid for all other APIs) should be responsible to include
  proper HTTP headers in their responses to either disallow caching of
  the response or at least limit it's validity.

  See the HTTP caching RFC section 5
  <https://tools.ietf.org/html/rfc7234#section-5> for headers that could
  be used to accomplish that.

  For sake of completeness; also see
  https://github.com/gophercloud/gophercloud/issues/727 for my initial
  client-side fix and related discussion with client-side project

  Expected result
  Openstack APIs to include header(s) from RFC7234 section 5 
<https://tools.ietf.org/html/rfc7234#section-5> to either disallow caching or 
to specify a meaningful lifetime or to force/implement revalidation options.

  Actual result
  No headers controlling caching present whatsoever.

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