[TriLUG] Load balancing DNS servers

[Joseph Mack NA3T via TriLUG]

On Fri, 3 May 2019, Mauricio Tavares via TriLUG wrote:

> How would you load balance them so you only have to provide a single
> IP to the clients?

LVS loadbalances readonly services. The loadbalancer is accessed through a 
single IP, that of the LVS director, but the reply comes from one of the 
loadbalanced servers behind the director. The reply has the src_addr of the 
director.

> If those servers also do DHCP, how would the updates be shared with each node 
> so everyone will be on the same page? What about leases?

I started with the ISC dhcpd. It's supposed to loadbalance and send updates of 
issued IPs to the other servers. However it doesn't take long (hours, depending 
on traffic) before some table fills up and you have to restart the servers. I 
never figured out the problem and no-one on the ISC mailing list was helpful.

However, AFAIK a dhcpd is not supposed to issue an IP that's already in use, 
even if it's in the range of IPs that the dhcpd server controls and even if that 
dhcpd _didn't_ issue that IP. (presumably you're allowed to come onto a network 
with a fixed IP in the dhcpd's controlled range, without messing up the 
network). I think the dhcpd pings for that IP before handing it out. So you can 
have multiple dhcpds running, all issuing IPs in the same range, without the 
dhcpd's colliding. I turned off the ISC updater and just left the two dhcpds 
running at the same time and it works fine.

Joe


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Joseph Mack NA3T EME(B,D), FM05lw North Carolina
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