[CentOS] high availability ideas

Sat Nov 19 09:10:10 UTC 2011
David Hrbáč <david-lists at hrbac.cz>

Dne 19.11.2011 03:35, Digimer napsal(a):
> WAN/Stretch clustering suffers most for network latency. If you need to
> keep the data in sync across both nodes, using DRBD will limit your hard
> drives, effectively, to the speed and latency of the link between your
> nodes at the different DCs. This is rarely usable.
> Stop by #linux-cluster and/or #drbd, I know there are folks there from
> Linbit and Hestaxo who could help you, but you're going to be facing
> rather expensive technical challenges. :)

DRDB over WAN is nonsense. There are many scenarios
expensive/non-expensive, depends on data you want to distribute. Being
you I would start with the simplest one. I can name a few:
- buy netapp and create metrocluster with RRDNS
- have your subnet routed into both datacenters and use virtual IPs
- webapp might be somewhat static, so files might be easy to sync, as to
DB data, start with master-slave replica and M/S swap, try to read data
from multiple source, write to only the one
- you are talking about two nodes, with your scenario only one will
serve the data in time, it's not horizontal scaling, try to use both in time
- have low ttl for DNS with RRDNS, add/remove records by nodes' status
- don't forget about webapp side of topic, webapp must be prepared to
save nonDB content
- start with two nodes in one dataceter to test your horizontal
scenario, you can than split it into two DC or easily add the
third/fourth nodes in another DC
- ....