[DRBD-user] drbdlinks useful?

[Saul, Markus]

> -----Ursprüngliche Nachricht-----
> Von: drbd-user-bounces at lists.linbit.com 
> [mailto:drbd-user-bounces at lists.linbit.com] Im Auftrag von 
> Stefan Seifert
> Gesendet: Dienstag, 14. Oktober 2008 11:21
> An: drbd-user at lists.linbit.com
> Betreff: [DRBD-user] drbdlinks useful?
> 
> [...]
> 
> I could now:
> * simply always link /etc/postfix to /shared/mail/etc/postfix 
> and have the 
> local one automatically hidden by mounting /shared/mail over it. Or
> * use drbdlinks to move away /etc/postfix and link it 
> to /shared/mail/etc/postfix
> 
> I now wonder, what's the better solution. With drbdlinks I 
> could have the 
> local config still available for modification even when my 
> mailserver is 
> down. But this is at the expense of added complexity to that 
> already very 
> complex cluster stuff. Also I could just do a bind mount of / 
> to somewhere 
> else if I need to access the local config while /shared/mail 
> is mounted.
> 
> So what's the real benefit of drbdlinks? Any practical experience?
> 
> [...]

Hello Stefan,
the question is: what do you want to do with postfix if your shared partition is not available or
if your cluster node is in an inactive role for the resource postfix?
It is quite likely you still may want to have email functionality. But you really do not want to have the same configuration
parameters active on two nodes in most cases, so a clean separation between local and cluster config should be done.
Another point is the question about software updates, which are done quite nicely if you still have the whole application 
available locally with its correct paths, and you therefore don't need to switch between the cluster nodes to do an update. 
This of course assumes that you copied the relevant data to the cluster (/shared/mail) and did not just move it there.
drbdlinks is from my experience a good tool to achieve the above goals, and it gives you a central place
to manage all the links from your applications in a "standard" kind of way, and by editing a single file.
Of course this all assumes you have a cluster manager software running, like Heartbeat, for which a resource agent
"drbdlinks" exists. The resource agent then manages the links for you (more correct: Heartbeat uses the agent to start/stop it).


Hope this helps,

 Markus