Three node cluster interconnect options?

[shaggy62]

Hello,
I'm going to be implementing two different three node clusters to provide HA for a number of java application servers and their hosted applications. The current plan is to use two nodes of each cluster as the master for a subset of applications and have the third node be failover for the first two nodes. Each node will be running RHEL 5.3 64-bit.

I've implemented simple two node clusters in the past and used cross over cables to enable the LLT interconnect. I'm curious as to how the interconnect can be configured in a three node setup. Is it a requirement that it be switched? If it must be switched and I use two interfaces per node, should each of the interfaces be cabled into a different switch? This would seem to cause the ISL in my switches to have to carry the LLT traffic, but using only one switch would be a single point of failure. Is using cross over cables in a meshed configuration a viable solution to interconnect in a three or more node cluster?

Any pointers are appreciated

Thanks

[Gaurav_S]

Hi There,

Yes, switch would be recommended rather than using meshed cross over cables.

Each nodes should have 2 NIC for heartbeats (minimum)...  So here is your hardware requirements:

2 Private NIC on each host (you can use public NIC as low pri link for additional redundancy)
2 different dedicated switch for heartbeat, If not then 2 different VLAN's in 2 different switch.

For e.g  lets say your 3 nodes are A, B & C   & lets say 2 switches or VLANs are  X & Y

One private NIC from A, B & C will connect to X
Another private NIC from A,B & C will connect to Y

So you achieved redundancy for NIC, redundancy for switch.  Also connect the switches to separate power source

Hope this helps....

Gaurav

[Marianne · Accepted solution]

This picture from the Install Guide says it all:
On the left is your traditional 2-node cluster and on the right how to connect more than 2 nodes.

[Leigh_Brown]

Hello,

I have tried to answer your specific questions :-

-- Is it a requirement that it be switched?
-- Is using cross over cables in a meshed configuration a viable solution to interconnect in a three or more node cluster?

This is the same question stated differently.  The answer is, you cannot use crossover cables for a three or more node cluster, and hence you must use one switch (or hub :) ) per private LLT link.  The reason you cannot use crossover cables is because LLT must be able to broadcast its updates to every other node, on a particular private link.  You can't cable up crossover links to support this.

-- If it must be switched and I use two interfaces per node, should each of the interfaces be cabled into a different switch?

To be precise, each set of NICs that form a private link network should be connected to a different switch.

-- This would seem to cause the ISL in my switches to have to carry the LLT traffic, [...]

This is not actually true.  The private link networks are totally independent of each other, so if all the NICs on the first private network are connected to a single switch, there will be no interswitch traffic required (in fact two isolated switches will do the job nicely).  If you are using VLANs, then the VLAN used on switch A for private network A, does not need to be defined on any of the ports on switch B (and vice versa).

Regards,

Leigh.

[shaggy62]

Thanks for all the answers and information. All the replies were very helpful and provided a clear path for the installation of my new clusters.