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[Chris Dent <cdent+lp@xxxxxxxxxxxxx>]

I've added api-sig to this because the fact that this issue has shown up
in the wild should be good motivation for us to make a guideline about
how to address it. The code for adding the requisite headers to
placement may be a useful starting point:
https://review.openstack.org/#/c/521640/


** Also affects: openstack-api-wg
   Importance: Undecided
       Status: New

** Changed in: openstack-api-wg
       Status: New => Confirmed

** Changed in: openstack-api-wg
   Importance: Undecided => Medium

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https://bugs.launchpad.net/bugs/1747935

Title:
  Openstack APIs and RFC 7234 HTTP caching

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

Bug description:
  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
  <https://tools.ietf.org/html/rfc7234#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
  owners...

  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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