A VM that changes its memory faster than the network carries it never
finishes a live migration without auto converge: measured with a guest
rewriting about 1.2 GB/s over an 8.5 Gbit/s link. The migration then
ran until gunicorn ended the request after 600 s. libvirt cancelled it
when the request went away and the VM stayed on the source, but the
user got an error page and nothing was logged.
The app now cancels a migration that has not finished after 540 s
(MIGRATION_TIME_LIMIT, below the 600 s of gunicorn.conf.py; a test
keeps it below). The failure is reported and logged like any other:
the migration was cancelled, the VM stays on the source host, and a
VM like that needs auto converge. A timer that fires as the migration
ends finishes before the compute locks are released, and an error
the cancel did not cause keeps its own message.
Migration needs the VM's disks on storage both hosts reach, and nothing
checked that. A VM with a disk the destination did not have failed
during a live migration; a shut-off VM's definition moved and could not
start there.
moveto now refuses the migration before anything changes, naming each
disk (target and source) that is not a volume of the destination's
active storage pools. Checked: the disks, CD-ROM images and block
devices of the live and the persistent definition, pool volumes, and
backing files, as the definition or the destination's volume lists
them (a shut-off VM's definition does not). Pools are refreshed before
a disk counts as missing, so a file another host made on shared
storage is found. Network disks and network backing images are
reached the same way from every host and are not checked; disk types
that cannot be checked (dir, nvme, ...) are refused.
This checks that the destination knows a volume, not that it is the
same file: shared storage should be a storage pool on each host. A
shared file outside any pool, or a block device no pool covers, is
refused.
moveto read the VM state for each flag and dropped options that did
not fit it, so a request could run as something else than asked; the
log then named the mode from the form ("live" or "offline"), not the
one used. The API did not log at all and answered "instance migrate is
started" after the migration had finished.
- moveto reads the state once. A running VM migrates live, or without
live paused for the transfer (non-live); a paused VM stays paused; a
shut-off VM moves offline. Live for a shut-off VM, offline for a
running or paused one, and any other state are refused before
anything changes. unsafe, auto converge (live only) and compressed
apply to a running VM.
- migrate_instance logs the outcome for the VM page and the API: the
mode and options used, or the error. The API answers
"instance is migrated (<mode>)" and accepts requests that leave out
an optional option.
- Post copy is gone from the form, the view and the API: only the
flag was set, and without migrateStartPostCopy, which the app never
called, the migration never switched to post copy.
libvirt's offline migration fails on some builds with "operation
failed: domain is no longer running" (RHEL-156800: Rocky/RHEL 9.8
libvirt 11.10.0-12 has the change that broke it, not the fix, which is
upstream in 12.2.0). A shut-off VM could not be migrated at all there.
A shut-off VM is only its definition, as the disks are on storage both
hosts share, so moveto now moves that itself:
- refused first when the VM has snapshots or a saved state, or the
destination already has a VM with its UUID or name;
- defined on the destination from the source's migratable XML, then
undefined on the source; NVRAM and TPM state stay on the source;
- after a failure the VM stays defined on one host: the destination
definition is removed only while the source still has its own, and
a VM another client started on the source meanwhile gets its
definition and autostart back there.
The destination's qemu migration hook does not run for it. Running and
paused VMs still migrate through libvirt.
Migration is client-driven: libvirt sends the VM's memory to the
destination's own host name unless a migration URI is given, and the
app never gave one. Where the hosts cannot resolve each other's names
(or the names point at a management network) every migration failed
with "Unable to resolve address '<host name>' service '49152'".
A compute now has an optional migration address (an IP address or a
host name, no scheme or port), editable in the compute form and the
API. A VM migrating to that compute is sent to tcp://<address>
(bracketed for IPv6). Empty, the default for existing computes, keeps
the previous behavior. The compute's host name is not reused, because
for SSH computes it can be an ssh_config alias.
The migration log entry names the address when one is set.
Migration left the VM defined on the source host unless "Delete
original" was ticked (VIR_MIGRATE_UNDEFINE_SOURCE). With the shared
storage migration needs, that definition points at the disks the
destination VM is running on: the VM showed on both hosts and could be
started (or autostarted) a second time against the same disks; only a
configured lock manager stops that.
moveto now always passes VIR_MIGRATE_UNDEFINE_SOURCE with
VIR_MIGRATE_PERSIST_DEST. The option is gone from the form, the view,
the API (MigrateSerializer.xml_del) and the clone auto-migration. It
removes the definition, not the disk files.
