Fix multifd compatibility with postcopy #15016
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// UPGRADE PATH IS 1. daemonsets - ensures all compute nodes are updated to handle new features 2. wait for daemonsets to roll over 3. controllers - ensures control plane is ready for new features 4. wait for controllers to roll over 5. apiserver - toggles on new features. After the virt-handler has been updated, it should be able to communicate with the older virt-launcher. In kubevirt#12705 a change of the ParallelMigrationThreads migrationOption has been introduced, which causes a wrong set of the libvirt migration options. In particular, previously the ParallelMigrationThreads migrationOption was set by the virt-handler, and the virt-launcher simply checks its presence or not, and adjusts the libvirt flags and params to enable the multifd. With kubevirt#12705 this paradigm changed, demanding the logic from the handler to the launcher; IOW, the handler sets the ParallelMigrationThreads, and the launcher decides whether set or not the libvirt flags and options to enable the multifd. With same version of handler and launcher, everything is working well, but during upgrades, the launcher version is different from the handler one. This is causing the migrations to fail due to: `Postcopy is not yet compatible with multifd`. Let's avoid setting the ParallelMigrationThreads option from the virt-handler, restoring the backward compatibility. Signed-off-by: fossedihelm <[email protected]>
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@xpivarc: new pull request created: #15178 DetailsIn response to this:
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What this PR does
// UPGRADE PATH IS
After the virt-handler has been updated, it should be able to communicate with the older virt-launcher.
In #12705 a change of the ParallelMigrationThreads migrationOption has been introduced, which causes a wrong set of the libvirt migration options. In particular, previously the ParallelMigrationThreads migrationOption was set by the virt-handler, and the virt-launcher simply checks its presence or not, and adjusts the libvirt flags and params to enable the multifd.
With #12705 this paradigm changed, demanding the logic from the handler to the launcher; IOW, the handler sets the ParallelMigrationThreads, and the launcher decides whether set or not the libvirt flags and options to enable the multifd.
With same version of handler and launcher, everything is working well, but during upgrades, the launcher version is different from the handler one.
This is causing the migrations to fail due to:
Postcopy is not yet compatible with multifdReferences
https://issues.redhat.com/browse/CNV-64362
Why we need it and why it was done in this way
The following tradeoffs were made:
The following alternatives were considered:
Links to places where the discussion took place:
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