From: Date: June 17 2006 8:59am
Subject: Re: cluster load balancer
List-Archive: http://lists.mysql.com/cluster/3726
Message-Id: <4493A86C.7040109@mysql.com>
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Hi Saul,

(Please reply to the mailinglist too)

Saul Waizer wrote:
> Geert,
> 
> I have a php web application that uses a regular connection string to the
> mysql node1, I have no idea how to really “use” the cluster, right now
> everything is being sent to one node, but if that node fails there is no
> true redundancy unless I point the connection to the second node
> 
> NODE1  <----> NODE2
>  |
>  | 
>  V       
> APPLICATION

Check out this URL and the diagram there:
   http://dev.mysql.com/doc/refman/5.0/en/mysql-cluster-overview.html

What you probably have is:

DATANODE <---> DATANODE
            |
	   |
       MYSQL NODE
	   |
            |
          Application

> According to this diagram if node one fails the application will fail as
> well because the connection string is directed to node1

You can't make your Application connect to a particular data node, only to a 
MySQL node. It's important to always mention what kind of node you are 
talking about, as there are 3 types :)

Your application is connecting to a 'MySQL node' (or 'API Node'). This MySQL 
node will then connect to one of the 'data nodes'.
If you have 2 data nodes and NoOfReplicas=2, then you data nodes are 
redundant: if one fails, your cluster will still be up! No need to do much here.

Again, you will need to do some load balancing or fail-over on MySQL nodes 
level. Add a second MySQL node and make it connect to the cluster. Then you 
have couple of options:
- your application connects to one, if the connection fails to the first 
MySQL node, it should use the second one.
- you run your application on both machines where MySQL nodes are running, 
and load balance between them
- you load balance between the MySQL nodes and make your application only 
connect to the load balancer, which should handle also the fail-over.

I would use second option, as you have your application redundant as well then.

Cheers,

Geert

-- 
Geert Vanderkelen, Support Engineer
MySQL GmbH, Germany, www.mysql.com

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