[Csync2] cysnc2 vs linking hackery

[Rafiu Fakunle]

Hi Michael,

Michael Mansour wrote:
> Hi Rafiu,
>
>   
>> Hi all,
>>
>> I've been reading about csync2 and want to find out whether it can 
>> be recommended for use in DRBD+HA setup instead of the metadata 
>> volume + FS links method. I've never liked the latter way of doing 
>> it and if csync2 is an option it certainly would solve a heck of a 
>> number of configuration problems for me.
>>     
>
> I'm not sure I full understand your requirements but I currently use csync2 
> in a DRBD+HA environment without any issues.
>
>   
OK maybe I should have elaborated a bit. Prior to the availability of 
csync2, the seemingly recommended way of keeping the application 
metadata in sync was to put the config files on a meta-disk (drbd 
volume) and then symlink to those files from the original locations.

so

/etc/httpd/httpd.conf :- /etc/httpd/httpd.conf -> 
/cluster_metadata/etc/httpd/httpd.conf

/var/lib/nfs :- /var/lib/nfs -> /cluster_metadata/var/lib/nfs 

etc etc.


> The clustering software I use is linuxha.net
IIRC it has the concept of a metadata device right? I.e one drbd volume 
for app symlinks?

> , which handles all the 
> heartbeat, failover, drbd, etc while csync2 just synchronises config files 
> between the machines.
>   
Interesting. I've been thinking of using it, but our application 
(http://www.openfiler.com) will get very stroppy if another application 
tries to do the volume management. It could still be integrated , but 
I'm guessing that may mean some significant rewriting of our app.


Csync2 for config files I understand. But what about stuff like 
/var/cache/samba/ directory or /var/lib/nfs directory?

> Have been using this for well over a year now with no dramas.
>
>   
Sounds great. I'm hoping we can use csync2. But I just need 
clarification on that one point about deploying for application 
metatdata. I can understand it might not be suitable for a database app 
eg. mysql but I'm talking purely about things like Samba, NFS, HTTPD, 
Proftpd et al.


Thanks for any further insight you may be able to provide.



R.

> Michael.
>
>   
>> I read in an ML post that csync2 is only recommended for slow 
>> changing config files. How would that apply to metadata for services 
>> like nfs , Samba/winbind etc. Could I use csync2 to replicate 
>> /var/lib/nfs and /var/cache/samba for instance?
>>
>> If csync2 is not the way to go, how about a cross between the 
>> metadata volume and some other [d|i]notify based solution where 
>> local changes (on active primary) are synced to the metadata volume 
>> and then synced back to place (on passive secondary), controlled as 
>> a heartbeat resource, when a failover occurs.
>>
>> TIA
>>
>> R.
>>     
>
>