Re: Cluster in WAN

[Mikael Ronström]

Marc Remolt wrote:
> Hi everybody,
> as I haven't found much usefull information about
> clustering mysql in a WAN, I'd like to ask some
> questions.
> Let me describe my intended setup first:
> I'd like to increase the availability of a MySQL
> driven web application by simply running it on two
> servers. If those two servers are in the same
> subnet, I'd gain availability with server
> problems, but not, if the network dies (router
> ...). So I thought it would be a good idea to put
> the two machines in different locations, if
> possible even on different backbones.
> What I do now is the usual replication which has
> the known disadvantages. The users can't just go
> to any of the two websites and make updates to the
> DB, I can have only one online at a time or risk
> async data. A cluster behind the two sites would
> result in me not having to care about that
> problem.
> Now my questions:
> The little I've found about this topic suggested,
> that clustering over the Internet could bring
> performance problems. The sites aren't under heavy
> load, maybe 5 writes/minute on average. Would that
> work over let's say a 2Mbit connection?

Currently it wouldn't since also reads would be using the network
but there is some development ongoing that makes it possible
to set connection preferences between MySQL Servers and
ndbd nodes so that reads are localised according to the configuration.
This would however only be applicable in a 2-data node cluster since
with more than one node group there are no mechanisms in the data
nodes to choose special nodes currently.

Even with this development it is important to notice that a dropped
TCP/IP connection is treated as a node failure and network partitioning
problem must be handled and configuration must be tuned with time-outs
accepting WAN delays.

> The second thing is security. Is there any way to
> encrypt the cluster communication? I was thinking
> about stunnel or simmilar products, but I'm not
> quite sure this will really work out. Any
> experience with this or any ideas?
>

MySQL Cluster uses ordinary TCP/IP sockets currently.

Rgrds Mikael

> Thanks for you bearing with me.
>
> Marc