[D] KVM: cross cluster migration - hidden feature? [cloudstack]

["ingox (via GitHub)" <gi...@apache.org>]

GitHub user ingox created a discussion: KVM: cross cluster migration - hidden feature?

I have two cluster running KVM and I have multiple storages (NFS) where some are zone wide and some are cluster wide.

By using the CloudStack UI I cannot migrate across cluster. I'm not able to select the host(s) on the other cluster. 
The documentation says that is not possible: https://docs.cloudstack.apache.org/en/latest/adminguide/virtual_machines.html#moving-instances-between-hosts-manual-live-migration

<img width="1093" height="742" alt="image" src="https://github.com/user-attachments/assets/9fa222dc-0d9e-4a62-b0c0-aedb1bf5ebd0" />


By using cloudmonkey I can migrate between clusters online. In case of cluster wide storage I need to migrate the storage too. No issues here.

It sounds like a UI bug but documentation would also need to change.

What is your experience?

GitHub link: https://github.com/apache/cloudstack/discussions/13963

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Re: [D] KVM: cross cluster migration - hidden feature? [cloudstack]

["winterhazel (via GitHub)" <gi...@apache.org>]

GitHub user winterhazel added a comment to the discussion: KVM: cross cluster migration - hidden feature?

@ingox cross-cluster live migration with KVM has been supported for a while, but the documentation was never updated.

The "UI bug" was actually a bug in the `findHostsForMigration` API, which the UI uses to show which hosts are suitable for migration. There was a regression in 4.20.3 and 4.22.1 that made it stop returning hosts from other clusters. It was fixed through #13452, which will be available in 4.22.2 and 4.23.0 (and 4.20.4, if this version releases).

One interesting note regarding the KVM live migration that I don't see mentioned often: it uses the libvirt connection between the hosts to transfer the disks, so direct migration between primary storages that are not shared by the source and destination hosts is also possible. I know this works for NFS, SharedMountPoint, and local storage (probably also for CLVM and CLVM_NG). However, there were a few regressions between versions 4.20 and 4.22 that blocked live migration to SharedMountPoint (without workarounds) and were not addressed yet (see #13390).

GitHub link: https://github.com/apache/cloudstack/discussions/13963#discussioncomment-18170108

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Re: [D] KVM: cross cluster migration - hidden feature? [cloudstack]

["weizhouapache (via GitHub)" <gi...@apache.org>]

GitHub user weizhouapache added a comment to the discussion: KVM: cross cluster migration - hidden feature?

it was supported since ACS 4.15 (#4534)
users need to set global setting `migrate.vm.across.clusters` to `true`

GitHub link: https://github.com/apache/cloudstack/discussions/13963#discussioncomment-18171735

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Re: [D] KVM: cross cluster migration - hidden feature? [cloudstack]

["ingox (via GitHub)" <gi...@apache.org>]

GitHub user ingox added a comment to the discussion: KVM: cross cluster migration - hidden feature?

@weizhouapache that is interesting. It was disabled in my case but didn't make a change in the UI after I enabled it.

@winterhazel If that is fixed in the next versions, that is great.

GitHub link: https://github.com/apache/cloudstack/discussions/13963#discussioncomment-18172542

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