Re: Two-machine cluster efficient approach(?) Comment? Thanks.

["Ragnar Kjørstad" <kernel@ragnark.vestdata.no>]

On Thu, May 24, 2001 at 06:32:10PM -0400, Chuck Wu wrote:
> Two machines want to be accessed by the same IP address and
> share workload. Can not change the router. Can only change 
> local linux system. Will the following approach work? Thanks.

You should check out Linux Virtual Server; it does something simular
(only it doesn't reply to arp-requests with broadcast-address, but with
one of the servers' ethernet-address).

> Solution:
> ---------
> 1. Reserve an unused IP as the to be publicized "Server IP", actually no
>    machine takes it. So, it is kind of "virtual IP".
> 2. Alias the NIC of those two work stations to this "virtual IP" so they
>    can accept packets to this "virtual IP".
> 3. For ARP request packet to this "virtual IP", those two work stations
>    will return the MAC broadcast address. Then, all the packets to the
>    "virtual IP" will be broadcast to this subnet and those two machines
>    will get such packtes.
> 4. Before such packets gets into the TCP/IP stack, use a hash function
>    to filter the packets. Say, workstation A will accept packets whose
>    source IP is an odd number and discard the packets with even-number
>    source IP.

If this work, a useful addon would be to use something a little more
advanced, to allow it to scale to more than 2 servers.

> 5. For the outgoing packets from those two workstations, change the source
>    IP address to be the "virtual IP".
> 6. Have another thread keep ping each other, once another workstation
>    crashes, change my hash function to accept all the packets to the
>    "virtual IP". Whenever another workstation resumes, switch back to
>    the original hash function.
> 
>    Do you think if this approach will work? There is also a question I
> am not quite sure, can two machines's NICs be aliased to the same "virtual
> IP"? Will it cause some conflicts? And, it seems I need to change the
> linux kernel source code. I am not pretty sure where is the location of
> the source code related to the above operations. Like, can you tell me the
> location of the linux kernel source code to answer an ARP request packet,
> to build a hash function to filter the incoming IP packets before it
> enters the TCP/IP stack?


--
Ragnar Kjørstad
Big Storage