Client Caching Of Negotiated Version¶

Problem description¶

When the ironicclient talks to the ironic server, there may be a mismatch in supported API versions. The client and server negotiate a version to be used in communicating, but since the ironicclient can be used as a user interactive client, this process of negotiation would be repeated for each command line invocation.

It would be useful, for each ironic server that the ironicclient talks to, to cache the version agreed upon for communication, so that each conversation between client and server does not require renegotiation.

This version caching would need to be per user, for each ironic server (host, network port pair specific) and would be time-bound (say 5 minutes), so any future upgrade of the client or server would benefit from supporting newer available versions.

Proposed change¶

The proposed implementation consists of caching the negotiated version information between an ironicclient and ironic server in local file storage for use by future invocations of the ironicclient.

This information would be cached for a specific period of time, before becoming stale and ignored.

Specifically, we are proposing:

• Using the dogpile.cache[1] caching system, a pre-existing library that is already included in global requirements[2]. It is currently used by os-client-config[3], which is used by openstackclient[4].
• Storing the cached information in local file storage, using appdirs[5] to provide the correct location
• Indexing the version information in an ironic-server:network-port pair (such as ‘example.com:1234’) so that multiple ironic servers running on the same IP address will be cached independently for each user invoking python-ironicclient
• Having a default period of 5 minutes for caching version information for each ironic server

Storing the version information in a well-known, standardised, local file storage location means that, if the user wants to, they can remove the cached version information manually triggering a renegotiation of the version to be used in communication between the client and server.

Implementation¶

Dependencies¶

None

Testing¶

Unit tests will be provided to verify this solution

Upgrades and Backwards Compatibility¶

None

Documentation Impact¶

None

References¶

• [0] API Microversions Spec: http://specs.openstack.org/openstack/ironic-specs/specs/kilo/api-microversions.html
• [1] Documentation on dogpile.cache is found here: https://dogpilecache.readthedocs.org/en/latest/
• [2] dogpile.cache is already specified in https://github.com/openstack/requirements/blob/master/global-requirements.txt
• [3] https://github.com/openstack/os-client-config
• [4] https://github.com/openstack/python-openstackclient
• [5] Documentation on appdirs is found here: https://pypi.org/project/appdirs
• [6] Original custom file cache solution: https://review.openstack.org/#/c/173674/1/
• [7] Current state of the implementation at the time of this spec being raised: https://review.openstack.org/#/c/173674/19
• [8] http://eavesdrop.openstack.org/irclogs/%23openstack-ironic/%23openstack-ironic.2015-05-11.log.html#t2015-05-11T19:38:04
• [9] https://review.openstack.org/#/c/173674/9