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5.4 KiB
ReStructuredText
206 lines
5.4 KiB
ReStructuredText
..
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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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==================================================
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Client Caching Of Negotiated Version
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==================================================
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https://bugs.launchpad.net/ironic/+bug/1526411
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This adds support for caching the version negotiated by the
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ironicclient, between itself and the ironic server. This is supplementary
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to the 'api microversion' spec approved in the Kilo release[0].
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Problem description
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===================
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When the ironicclient talks to the ironic server, there may be a mismatch
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in supported API versions. The client and server negotiate a version to be
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used in communicating, but since the ironicclient can be used as a user
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interactive client, this process of negotiation would be repeated for each
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command line invocation.
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It would be useful, for each ironic server that the ironicclient talks to,
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to cache the version agreed upon for communication, so that each conversation
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between client and server does not require renegotiation.
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This version caching would need to be per user, for each ironic server (host,
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network port pair specific) and would be time-bound (say 5 minutes), so any
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future upgrade of the client or server would benefit from supporting newer
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available versions.
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Proposed change
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===============
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The proposed implementation consists of caching the negotiated version
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information between an ironicclient and ironic server in local file storage
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for use by future invocations of the ironicclient.
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This information would be cached for a specific period of time, before
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becoming stale and ignored.
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Specifically, we are proposing:
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* Using the dogpile.cache[1] caching system, a pre-existing library that is
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already included in global requirements[2]. It is currently used by
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os-client-config[3], which is used by openstackclient[4].
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* Storing the cached information in local file storage, using appdirs[5] to
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provide the correct location
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* Indexing the version information in an ironic-server:network-port pair
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(such as 'example.com:1234') so that multiple ironic servers running on
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the same IP address will be cached independently for each user invoking
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python-ironicclient
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* Having a default period of 5 minutes for caching version information for
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each ironic server
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Storing the version information in a well-known, standardised, local file
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storage location means that, if the user wants to, they can remove the cached
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version information manually triggering a renegotiation of the version to be
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used in communication between the client and server.
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Alternatives
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------------
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An alternative file-based solution was proposed[6], but rejected in favour of
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using dogpile.cache.
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The suggestion to move to dogpile.cache was made both in the code review[9]
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and was discussed in IRC[8].
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Reasons for using dogpile.cache included: commonality with existing file
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caching libraries used elsewhere in OpenStack, and use of tested common
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libraries typically means less bugs.
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Data model impact
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-----------------
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None
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State Machine Impact
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--------------------
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None
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REST API impact
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---------------
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None
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Client (CLI) impact
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-------------------
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This spec only affects the python-ironicclient, not ironic server.
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RPC API impact
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--------------
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None
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Driver API impact
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-----------------
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None
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Nova driver impact
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------------------
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None
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Ramdisk impact
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--------------
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N/A
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.. NOTE: This section was not present at the time this spec was approved.
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Security impact
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---------------
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None
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Other end user impact
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---------------------
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None
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Scalability impact
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------------------
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This change potentially reduces network traffic between the client and server
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and hence aids scalability.
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Performance Impact
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------------------
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This change potentially reduces network traffic between the client and server
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and hence improves latency between when a request is made to ironic and when
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the response is received.
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Other deployer impact
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---------------------
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None
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Developer impact
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----------------
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None
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Implementation
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==============
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Assignee(s)
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-----------
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Primary assignee:
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mrda - Michael Davies <michael@the-davies.net>
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Work Items
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----------
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* The implementation of this spec has already commenced - see [7]
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Dependencies
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============
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None
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Testing
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=======
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Unit tests will be provided to verify this solution
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Upgrades and Backwards Compatibility
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====================================
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None
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Documentation Impact
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====================
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None
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References
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==========
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* [0] API Microversions Spec:
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http://specs.openstack.org/openstack/ironic-specs/specs/kilo/api-microversions.html
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* [1] Documentation on dogpile.cache is found here: https://dogpilecache.readthedocs.org/en/latest/
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* [2] dogpile.cache is already specified in
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https://github.com/openstack/requirements/blob/master/global-requirements.txt
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* [3] https://github.com/openstack/os-client-config
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* [4] https://github.com/openstack/python-openstackclient
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* [5] Documentation on appdirs is found here: https://pypi.python.org/pypi/appdirs
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* [6] Original custom file cache solution: https://review.openstack.org/#/c/173674/1/
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* [7] Current state of the implementation at the time of this spec being
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raised: https://review.openstack.org/#/c/173674/19
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* [8] http://eavesdrop.openstack.org/irclogs/%23openstack-ironic/%23openstack-ironic.2015-05-11.log.html#t2015-05-11T19:38:04
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* [9] https://review.openstack.org/#/c/173674/9
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