[one-dev] Live migration / recovery - suggestions

Mon Jan 20 22:26:07 PST 2014

I don't know why I'm offering more solutions to you, but anyway.

>From what I can see the state trace for a successful migrate is
RUNNING->MIGRATE->RUNNING, and that it is the same for a failed migrate.
You could write a hook that triggers on state RUNNING and checks for
previous state MIGRATE. The issue is you would have to maintain some state
info in your add-on by writing a "start migration" flag in your pre-migrate
script that gets cleaned up by your post-migrate script, when migrate
succeeds, or the proposed hook when the migrate fails. Alternatively you
could forgo maintaining your own state and use the hook to parse the VM's
log for migration failed messages.

A permanent fix would be for OpenNebula to add a new state MIGRATE_FAILED
that a developer could use to distinguish between a successful and failed
migrate. The failed migrate state trace would then be
RUNNING->MIGRATE->MIGRATE_FAILED->RUNNING

Regards,
David

On Mon, Jan 20, 2014 at 3:23 PM, Gareth Bult <gareth at linux.co.uk> wrote:

>
>    1. OK, so you are quite defensive and rude about this for some reason
>
> You are suggesting modifying and maintaining (currently) 5 migrate
> scripts, then redistributing (and keeping up-to-date)
> 90 other scripts, just to cope with a current deficiency with the current
> mechanism available for add-ons with regards to
> hooking into the current infrastructure.
>
> That was me being restrained.
>
> >I know it's not as elegant as the four line solution but point 2.
>
> To put it mildly.
>
> I'm *not* trying to insist my solution is included, but there needs to be
> "a" solution and generating lots more
> duplicate code to install and redistribute simply isn't "it" and I'm more
> than a little shocked anyone would suggest it!
>
>
> --
> *Gareth Bult*
> “The odds of hitting your target go up dramatically when you aim at it.”
> See the status of my current project at http://vdc-store.com
>
>
> ------------------------------
> *From: *"David Macleod" <dmacleod at csir.co.za>
> *To: *"Gareth Bult" <gareth at linux.co.uk>
> *Cc: *"Jaime Melis" <jmelis at opennebula.org>, dev at lists.opennebula.org
> *Sent: *Monday, 20 January, 2014 12:50:14 PM
>
> *Subject: *Re: [one-dev] Live migration / recovery - suggestions
>
>
>    1. OK, so you are quite defensive and rude about this for some reason.
>    2. The OpenNebula project has just said they don't want to change
>    their code base to suit you, so your four line solution is off the table.
>    3. You don't need to write the vmm drivers from scratch. Just copy the
>    three provided with ONE call them kvm-vdc, xen-vdc and vmware-vdc or
>    something, then make your customization to them. I know it's not as elegant
>    as the four line solution but point 2.
>
>
>
> On Mon, Jan 20, 2014 at 2:23 PM, Gareth Bult <gareth at linux.co.uk> wrote:
>
>> Once I switch to a different vmm (say "vdc" rather than "kvm") , how will
>> the system know to fall back on
>> the hypervisor in use for all the other scripts that I don't want to
>> modify?
>>
>> --
>> *Gareth Bult*
>> “The odds of hitting your target go up dramatically when you aim at it.”
>> See the status of my current project at http://vdc-store.com
>>
>>
>> ------------------------------
>> *From: *"David Macleod" <dmacleod at csir.co.za>
>> *To: *"Gareth Bult" <gareth at linux.co.uk>
>> *Cc: *"Jaime Melis" <jmelis at opennebula.org>, dev at lists.opennebula.org
>> *Sent: *Monday, 20 January, 2014 11:57:31 AM
>>
>> *Subject: *Re: [one-dev] Live migration / recovery - suggestions
>>
>> No, you should write a basic framework around the migrate script that
>> supports the three hypervisors that OpenNebula uses.
>>
>> >>> Gareth Bult <gareth at linux.co.uk> 2014/01/20 02:15 PM >>>
>>
>> Erm, yeah, Ok, should I include filters for the coffee machine too ?!
>>
>> --
>> *Gareth Bult*
>> “The odds of hitting your target go up dramatically when you aim at it.”
>> See the status of my current project at http://vdc-store.com
>>
>>
>> ------------------------------
>> *From: *"David Macleod" <dmacleod at csir.co.za>
>> *To: *"Gareth Bult" <gareth at linux.co.uk>
>> *Cc: *"Jaime Melis" <jmelis at opennebula.org>, dev at lists.opennebula.org
>> *Sent: *Monday, 20 January, 2014 11:50:26 AM
>> *Subject: *Re: [one-dev] Live migration / recovery - suggestions
>>
>> Then distribute a vmm driver per hypervisor...
>>
>> >>> Gareth Bult <gareth at linux.co.uk> 2014/01/20 02:01 PM >>>
>> .. Erm, because the vmm driver is per-hypervisor .. and this product is
>> technically
>> hypervisor agnostic .. ??
>>
>>
>> --
>> *Gareth Bult*
>> “The odds of hitting your target go up dramatically when you aim at it.”
>> See the status of my current project at http://vdc-store.com
>>
>>
>> ------------------------------
>> *From: *"David Macleod" <dmacleod at csir.co.za>
>> *To: *"Gareth Bult" <gareth at linux.co.uk>, "Jaime Melis" <
>> jmelis at opennebula.org>
>> *Cc: *dev at lists.opennebula.org
>> *Sent: *Monday, 20 January, 2014 11:32:33 AM
>> *Subject: *Re: [one-dev] Live migration / recovery - suggestions
>>
>> Hi Gareth, Jaime
>>
>> Why can't the recovery be handled by the migrate script? You can
>> distribute your own custom vmm driver so that it doesn't get overwritten by
>> the updates. That's how I wrote my add-on, I also have the need to recover
>> from a migrate fail.
>>
>> Regards,
>> David
>>
>> >>> Jaime Melis <jmelis at opennebula.org> 2014/01/20 12:43 PM >>>
>> Hi Gareth,
>>
>> we've been studying your proposal, and even though we agree with what you
>> say we
>> aren't 100% convinced with this solution. The issues with the proposal
>> are the
>> following:
>>
>> - As long as it's possible, we'd like to keep separate the main
>> opennebula code
>> and the addons. In this case it means that we are not very comfortable
>> with
>> point 3: adding addon-specific code to the main repository.
>>
>> - The proposed solution only solves the "migrate" issue, but other addons
>> will
>> have potentially issues with other scripts, and not necessarily with the
>> "CleanUp" part of the "ssh_exec_and_log". We would like to find a more
>> general
>> solution.
>>
>> We are still thinking about this, we definitely want to solve this issue,
>> so if
>> you (or anyone else) has any ideas, please let us know.
>>
>> cheers,
>> Jaime
>>
>>
>> On Tue, Jan 14, 2014 at 2:23 PM, Gareth Bult <gareth at linux.co.uk> wrote:
>>
>>> Hey Guys, I've done a little work on the migration script - this is
>>> what I've done here ..
>>> - be nice if something similar could be implemented @ source .. ?
>>>
>>> 1. ssh_exec_and_log (generic change - this could be useful elsewhere..)
>>> modify as follows;
>>>
>>> function ssh_exec_and_log
>>> {
>>> message=$2
>>> cleanup=$3 # ++
>>>
>>> EXEC_LOG_ERR=`$1 2>&1 1>/dev/null`
>>> EXEC_LOG_RC=$?
>>>
>>> if [ $EXEC_LOG_RC -ne 0 ]; then
>>> log_error "Command \"$1\" failed: $EXEC_LOG_ERR"
>>> if [ ! -z $cleanup ]; then # ++
>>> $cleanup # ++
>>> fi # ++
>>>
>>> if [ -n "$2" ]; then
>>> error_message "$2"
>>> else
>>> error_message "Error executing $1: $EXEC_LOG_ERR"
>>> fi
>>> return $EXEC_LOG_RC
>>> fi
>>> }
>>> i.e. allow a third parameter which is a function to call if the exec
>>> fails.
>>>
>>> 2. migrate (for my vdc code), add "CleanUp" as a last parameter on the
>>> exec_and_log on the last line
>>>
>>> ssh_exec_and_log "virsh --connect $LIBVIRT_URI migrate --live $deploy_id
>>> $QEMU_PROTOCOL://$dest_host/system" \
>>> "Could not migrate $deploy_id to $dest_host" CleanUp
>>> 3. Then add the following function to migrate;
>>>
>>> function CleanUp
>>> {
>>> VDC=$(dirname $0)/../../../vdc-nebula
>>> if [ -d "${VDC}" ]; then
>>> ${VDC}/remotes/tm/vdc/postmigrate_fail ${deploy_id} ${dest_host}
>>> fi
>>> }
>>>
>>> Cleanup could be extended for other storage options ... ??
>>> I guess ideally you would pass the driver through and CleanUp would
>>> become completely generic and postmigrate_fail
>>> would become just another standard routine??
>>>
>>>
>>>
> --
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