Apache and MySQL Cluster on two servers?

[Spynat]

Hi,

i have read the howtos regarding clustering MySQL and Apache and although I am not really a Linux-geek, I have to compliment the author for his work. I haven't tried setting up my own MySQL/Apache-cluster yet, because I have two questions that still bother me.

1. I would like to set up the cluster on two servers only, one containing the apache webserver, mysql database, loadbalancer and cluster management server and the other server containing another webserver, another mysql database and the second loadbalancer. The two loadbalancers should monitor each other and if one Apache or MySQL node fails, the other one should take over. Performance is not really an issue to me, but availability has to be provided.

Since it is possible to set up an apache cluster with two servers, I assume that it is also possible to set up a cluster that fulfills my needs with just two servers also. Is this correct or am I missing some important detail from the howtos?

2. I understand that the cluster management server is needed in order to keep the data nodes synchronized even if one node fails. Doesn't having just one cluster management server imply that there is a single point of failure in the setup? What happens if the cluster management server fails?

Thanks for your help,

Michael

[falko]

Have a look here: http://www.howtoforge.com/forums/showpost.php?p=30447&postcount=2

[Spynat]

In the thread you are referring to you state: "I don't know if you can combine the 4 load balancers on just two machines and then put both Apache nodes and MySQL nodes on the same two machines. But even if it works, you need a third node for the MySQL cluster management node."

Why do I need a third node? In your MySQL Cluster Howto one of the MySQL nodes is also the cluster management node.


Your post still doesn't answer my second question: What happens if the cluster management node fails?


Michael

[falko]

Have a look at this tutorial: http://www.davz.net/static/howto/mysqlcluster

I quote from it:

The Managment Server

I strongly recommend that you do not stop the managment server once it has started. This is for several resons:

* The server takes hardly any server resources
* If a cluster falls over, you want to be able to just ssh in and type ndbd to stat it. You dont want to have to start messing around with another server
* If you want to take backups then you need the managment server up
* The cluster log is sent to the management server so to check what is going on in the cluster or has happened since last this is an important tool
* All commands from the ndb_mgm client is sent to the management server and thus no management commands without management server.
* The managment server is required in case of cluster reconfiguration (crashed server or network split). In the case that it is not running, "split-brain" scenario will occure. The management server arbitration role is required for this type of setup to provide better fault tollerance.

However you are welcome to stop the server if you prefer.