Re: [Xen-devel] Remus: how to make remus end gracefully ? / how to change frequency on the run ?

[Brendan Cully <brendan@xxxxxxxxx>]

On Tuesday, 13 July 2010 at 10:30, Kyungjin Yoo wrote:
> 
> Hello
> 
> I recently installed xen 4.0.1-rc2 on Ubuntu Jaunty and tried Remus.
> 
> While I am testing remus, I need to figure out these two things below for
> my goal, but I failed to do that until now.
> If Brendan or anyone else here has any idea, please help me out. then I
> will appreciate it.
> 
> 1. Graceful finish of Remus.
> 
> Once I run remus, how could I stop it gracefully?
> When I try to finish remus, I couldn't find any command.
> and if I kill remus process, it seems to work as a fault. so it fails over
> to secondary server, and only domain at secondary server works, but
> original domain doesn't.
> so what if I stop remus but still want to use 1'st server domain?
> I think this is necessary in some cases, in general.

The UI is certainly primitive. There is a keyboard listener in the
remus main loop meant for testing failover at each of the remus
stages (have a look at the 'remus' control script, it's quite
short). It won't help you to return to having only a primary, since
there's no communication channel with the remus backend in that tool.

The simple answer is to xm destroy the VM on the backup. Remus will
notice that the backup has been lost and kill itself, leaving the
primary running as before.

> 2. Checkpoint frequency change on the run.
> 
> I would like to change frequency while remus is running.
> It seems that current remus is not implemented that way. once it starts
> with a specific frequency (with -l options), then we can never change the
> value until we start. Is this correct?
> If it is possible to change while running, let me know how to do that.
> 
> if this is not possible, I would like to try to modify the remus source and
> implement it for this function (frequency change on the run).
> How could I approach this? and how positive could it be?
> I can also change frequency after stop and start of remus with new
> frequency value, if new implementation is challenging.
> but in that case, I need an answer for the No 1 question above regarding
> "graceful finish of remus", which I don't know how to do that now.

This should be very easy: add a new command to 'getcommand' in the
main tool to get a new interval and update cfg.interval. I don't think
it'll be more than about 5 lines.

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