[one-dev] Live migration / recovery - suggestions

Tue Jan 21 06:33:52 PST 2014

Hi,

as far as we can see there are two issues here:

(1) how can addons modify and manage the original OpenNebula source code
(2) how to implement a custom action after a migrate failure, specifically
for this addon

We have been trying to find a good solution for (1), but since we haven't
found any proposal that fits in nicely, we've decided to focus only on
solving (2) for the moment. We don't want to mix the addon's code into the
main repository, so we came up with this proposal (which is basically
something in between the 'b' option that Gareth suggested in his last email
and David's last paragraph of his last email):

We are going to introduce a new generic action that will be called when an
action fails. In the particular case of the 'migrate' action, if 'migrate'
fails OpenNebula will check if there's a 'migrate.fail' script for that
particular vmm (this file is not supplied by OpenNebula). If it finds this
file, it will execute it. OpenNebula will never package an "<action>.fail"
file, therefore addon users will be able to upgrade safely without having
their content overwritten by the packaging systems. And addon creators
simply need to drop that file in the appropriate remotes/vmm/<hypervisor>
directory and they're good to go.

Gareth, David, do you like this proposal? Do you think it's a fair
compromise that solves the issue at hand while not being specific to this
addon?

Thanks for your input, guys.

Cheers,
Jaime

On Tue, Jan 21, 2014 at 11:02 AM, Gareth Bult <gareth at linux.co.uk> wrote:

> >A permanent fix would be for OpenNebula to add a new state MIGRATE_FAILED
>
> Absolutely!
>
> If you look at the very first posting on this thread, I explain my issue
> and ask;
>
> >How to do I do this, I guess effectively I need something like
> "postmigrate_fail" .. ???
>
> And Ruben replies;
>
> >As the migrate script can be easily updated we do not provide any hook
> for that. I'd go to kvm/migrate, and do a simple if [ $? ... after the
> virsh command to kill the cache on the target host.
>
> So we've sort of come full circle.
>
> I can see four possible solutions;
>
> a. Every time someone installs such a plugin, they modify ON source code
> (current)
> b. ON include the driver name to 'migrate' so 'migrate' can be used to
> call a plugin style cleanup script (sample supplied)
> c. ON provide for a script that's activated when a migration fails (which
> is the same as (b) really) ['real' solution]
> d. I don't use ON to provide this functionality at all but instead use the
> scripts / hooks in 'libvirt'
>     (so it's transparent to ON)
>
> I will be doing some work with the libvirt API to get proper snapshot
> integration as currently ON does not
> provide a snapshot interface beyond that provided by libvirt, so I will
> investigate (d) at the same time as this
> may be a simpler solution, albeit it means distributing files for libvirt
> as well as ON.
>
> Regards,
> Gareth.
>
>
> --
> *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: *Tuesday, 21 January, 2014 6:26:07 AM
>
> *Subject: *Re: [one-dev] Live migration / recovery - suggestions
>
> 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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>
>

-- 
Jaime Melis
Project Engineer
OpenNebula - Flexible Enterprise Cloud Made Simple
www.OpenNebula.org | jmelis at opennebula.org
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