iPXE to use Swift Temporary URLs

This blueprint adds support for generating Swift temporary URLs for the
deploy and image's ramdisk(s) and kernel(s) when booting with iPXE.

This blueprint depends on the blueprint ipxe-dymic-config that makes
the iPXE configuration files to be dynamically generated.

Change-Id: Ibae6e6401fa0458b8ecc74b47a213d587f4974a5

specs/liberty/ipxe-swift-tempurls.rst

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+..
+ This work is licensed under a Creative Commons Attribution 3.0 Unported
+ License.
+
+ http://creativecommons.org/licenses/by/3.0/legalcode
+
+================================
+iPXE to use Swift Temporary URLs
+================================
+
+https://blueprints.launchpad.net/ironic/+spec/ipxe-swift-tempurls
+
+This blueprint adds support for generating Swift temporary URLs for the
+deploy and image's ramdisk(s) and kernel(s) when booting with iPXE.
+
+Problem description
+===================
+
+Currently the iPXE driver requires an external HTTP server to serve
+the deploy and image's ramdisk and kernel. When used with Glance, the
+``ironic-conductor`` fetches the images from it and place them under the
+HTTP root directory, and if a rebalance happens in the hash right the
+new ``ironic-conductor`` taking over the node have to do the same thing,
+fetch the images and cache it locally to be able to manage that node.
+
+Having an external HTTP server should not be required when Glance is used
+with a Swift backend, with Swift we can generate temporary URLs that can
+be passed to iPXE to download the images without requiring credentials.
+
+Proposed change
+===============
+
+The proposed implementation consists in having the iPXE driver to create
+a Swift tempurl for the ramdisk and kernel (deploy or image) that the
+node will boot as part of the config generation.
+
+This blueprint also proposes adding a boolean configuration option under
+the ``ipxe`` group called ``use_swift``. If True this will tell iPXE to
+not cache the images in the disk and generate the Swift tempurl for the
+ramdisk and kernel, if False, iPXE will continue to cache the images
+under the HTTP root directory. Defaults to False.
+
+Alternatives
+------------
+
+Continue to use an external HTTP server and caching the images on
+the disk.
+
+Data model impact
+-----------------
+
+None
+
+State Machine Impact
+--------------------
+
+None
+
+REST API impact
+---------------
+
+None
+
+Client (CLI) impact
+-------------------
+
+None
+
+RPC API impact
+--------------
+
+None
+
+Driver API impact
+-----------------
+
+None
+
+Nova driver impact
+------------------
+
+None
+
+Security impact
+---------------
+
+There's a positive security impact because the Swift temporary URLs does
+have an expiration time and the images in the external HTTP server will
+be available until the instance is destroyed.
+
+Other end user impact
+---------------------
+
+None
+
+Scalability impact
+------------------
+
+There is a scaling benefit to download directly from Swift since a Swift
+cluster can be scaled horizontally by adding new nodes.
+
+Performance Impact
+------------------
+
+None
+
+Other deployer impact
+---------------------
+
+None
+
+Developer impact
+----------------
+
+None
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee:
+  lucasagomes <lucasagomes@gmail.com>
+
+Other contributors:
+
+
+Work Items
+----------
+
+* Add the new ``use_swift`` configuration option under the ``ipxe`` group.
+
+* Get the iPXE driver to generate the Swift temporary URLs as part of
+  the configuration generation when ``use_swift`` is True.
+
+* Skip caching the image on the disk when ``use_swift`` is True.
+
+Dependencies
+============
+
+* This patch depends on the blueprint `ipxe-dymic-config
+  <https://review.openstack.org/#/c/177726/>`_ that makes the iPXE
+  configuration files to be dynamically generated.
+
+Testing
+=======
+
+Unittests will be added.
+
+Upgrades and Backwards Compatibility
+====================================
+
+None
+
+Documentation Impact
+====================
+
+The iPXE documentation will be updated to reflect the changes made by
+this spec.
+
+References
+==========
+
+.. [#] http://docs.openstack.org/kilo/config-reference/content/object-storage-tempurl.html