Remove openvswitch runtime version checks
Specification for removing the runtime openvswitch version checks and replacing them with an external script that specifically tests the functionality required of openvswitch. Change-Id: Id497149fd0ea32be31e32cb5308e4a9640e9e763
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Terry Wilson
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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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Remove openvswitch run-time version checks
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==========================================
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Launchpad blueprint:
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https://blueprints.launchpad.net/neutron/+spec/remove-openvswitch-version-check
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The current method of checking openvswitch and kernel versions for specific
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feature support is brittle, distro-specific and unsupportable.
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Problem description
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===================
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When VXLAN tunnels are enabled, openvswitch-using agents call ovs_lib code to
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check that the installed kernel and openvswitch versions are greater than a
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minimum specified version. Due to distro-specific differences in 1) the fields
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returned by modinfo and 2) the minimum required version due to the practice of
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backporting, this run-time checking method fails.
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In addition to VXLAN, other specific openvswitch features will need to be
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tested for in the future. As the number of features and versions and distros
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grows, checking version numbers becomes increasingly unsustainable and should
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not be done at agent start, but instead at package installation or deployment.
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Proposed change
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===============
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Trying to test features by version numbers across multiple distros is a fool's
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errand. It is much better to leave dependency management to the distros and
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packaging as they are the only ones who really know what version dependencies
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exist in their environment. The run-time checks should be completely removed
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from ovs_lib and the agents.
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If an attempt is made to use a specific openvswitch feature fails, a helpful
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error message suggesting that updating openvswitch *may* resolve the issue
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should be logged.
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To help deployment tools, a script will be created that attempts to use
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specific openvswitch features and exits 0 for success and 1 for failure. This
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way a deployment can be aborted, e.g. in devstack, if the feature is enabled
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but not available in the current openvswitch/kernel versions without trying
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to keep track of version numbers or incurring a messy run-time feature check
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at agent start.
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Alternatives
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------------
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Openvswitch does not have the ability to query whether it supports certain
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features, so the only way to reliably test whether a feature exists at runtime
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is to try to use the feature and see if it works. It would be possible, but
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unacceptably messy, to attempt to use all required OVS features at agent start
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and exit the agent on failure. Dependency management should be handled at
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packaging and/or deployment and not checked every time an agent is started by
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modifying system state.
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Data model impact
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-----------------
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N/A
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REST API impact
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---------------
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N/A
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Security impact
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---------------
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N/A
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Notifications impact
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--------------------
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N/A
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Other end user impact
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---------------------
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N/A
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Performance Impact
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------------------
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Negligible improvement in openvswitch-using agents due to removal of checks.
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Other deployer impact
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---------------------
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Existing deployments will be unaffected as they will already have the
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appropriate dependencies for their deployment.
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Deployments using distro packaging will be unaffected as the dependencies will
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already be handled by the packaging.
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Source installs, e.g. devstack, should run the feature test script to verify
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that an appropriate version of openvswitch has been installed on the system.
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Developer impact
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----------------
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Agents using openvswitch will no longer need to check openvswitch versions
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when using version-specific openvswitch features. Testing is simplified since
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the version-check feature is being removed and no longer requires testing.
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Devstack can also be modified to run the external feature test script before
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deployment and fail early in the case of a configuration/dependency mismatch.
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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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otherwiseguy
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Work Items
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----------
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* Remove runtime version checks and associated tests
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* Create the feature test script
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This will essentially be a refactoring of:
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https://review.openstack.org/#/c/88121/
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into two pieces, the runtime check -> separate script and the existing code
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removal in that patch.
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Dependencies
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============
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N/A
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Testing
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=======
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As this implementation primarily removes code that should not exist, it also
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removes the need for testing the version checking code.
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Documentation Impact
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====================
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N/A
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References
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==========
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N/A
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