Subject: Re: [vserver] Re: [Freedombox-discuss] [vserver] Re: A software architecture for the FreedomBox
From: Gordan Bobic <gordan@bobich.net>
Date: Fri, 15 Apr 2011 11:45:03 +0100

Jon Bendtsen wrote:
> On 15/04/2011, at 12.20, Gordan Bobic wrote:
> 
>> Jon Bendtsen wrote:
>>> On 15/04/2011, at 01.01, Martin Fick wrote:
>>>> --- On Thu, 4/14/11, Gordan Bobic <gordan@bobich.net> wrote:
>>>>>> --- On Thu, 4/14/11, Gordan Bobic<gordan@bobich.net>
>>> [cuuuuuut]
>>>>> However
>>>>> - what use-case do you have where one guest will fail
>>>>> unrecoverably on one machine but resumes working on another
>>>>> machine with the exact same FS? In what case would a single
>>>>> guest fail without all of them failing?
>>>> Think load balancing.  Say 10 vservers, split them
>>>> so that 5 run on each host normally.  If either host
>>>> goes down, the other one picks up the slack.
>>>> Everything runs slower, but at least it still runs.
>>> I think about the same considerations at the moment, planning
>>> a new setup.
>>> Why not make 2 DRBD shares, A and B, put half of the vserver
>>> guests on the A storage, unify, them, and then put the other
>>> half on the B share. All the vserver guests on the A DRBD
>>> share runs on the A-host, and like wise with the B host. In
>>> daily usage you have no open files from the B share on the A
>>> host, so all the memory would be unified. In case of a split
>>> brain you can keep the guests running, and once you get
>>> connection again easily resync the DRBD.
>>> In case of 1 vserver host failing then you can just start
>>> all the vserver guests in DRBD share A on the vserver host
>>> B. Yes that will not unify both groups of hosts, but that
>>> should only be until you get the A host up again.
>>> So, what do you think?
>> I still don't see the advantage of using DRBD for block-level replication here. The
extra complication of having to deal with FS level fail-over doesn't seem to buy you
anything compared to the lsyncd mirroring setup.
> 
> can you guide me to a good lsyncd howto?

Not over and above what is available here:
http://code.google.com/p/lsyncd/

I haven't switched to using v2.x yet, but the latest 1.x works fine for me.

> can lsyncd replicate ACL? Can it replicate non linux vserver guests?
> (i'd rather have one sync system that does it all, than having
> multiple systems)

By default, it can sync everything rsync can. You can even use something 
other than rsync if it servers your purpose better.

Gordan