Add warning against hvparam changes with live migrations

Changing certain hvparams while an instance is running leads to a
dangerous situation for the instance. When the instance undergoes live
migration without having undergone a reboot that would have applied the
parameters, it is setup with the modified hvparams, and loaded with the
state relying on the old hvparams. Depending on what is used and how,
this might lead to a crash of the instance.

While a proper fix should go into a stable version of Ganeti as this is
not a trivial change, the least we can do is warn users that hvparam
changes may be dangerous.

Signed-off-by: Hrvoje Ribicic <riba@google.com>
Reviewed-by: Klaus Aehlig <aehlig@google.com>

diff --git a/lib/client/gnt_instance.py b/lib/client/gnt_instance.py
index 3f26fcf..19e7509 100644 (file)
--- a/lib/client/gnt_instance.py
+++ b/lib/client/gnt_instance.py
@@ -1370,6 +1370,10 @@ def SetInstanceParams(opts, args):
              " only at the next (re)start of the instance initiated by"
              " ganeti; restarting from within the instance will"
              " not be enough.")
+    if opts.hvparams:
+      ToStdout("Note that changing hypervisor parameters without performing a"
+               " restart might lead to a crash while performing a live"
+               " migration. This will be addressed in future Ganeti versions.")
   return 0