load balancer best practices

[Aristedes Maniatis]

With the changes in CARP as part of FreeBSD 10 I have some questions about the best way to do some things.


1. On a load balancer (haproxy) we might have the machine handling 100 or 5000 IP addresses. It would be simplest to just define a /24 (or more) range on the external interface (or in CARP) but then I cannot bind to each address.

Linux has something like net.ipv4.ip_nonlocal_bind. There appears to be nothing similar for FreeBSD. Do I need to define a /32 and alias each address?

a. is there a cleaner way?
b. will that cause performance issues if I create many hundreds of /32 aliases on the interface?



2. If I need to define a large number of aliases in CARP I'll quickly run out of vhids which I understand to go up to 256. What is the real meaning of vhid in a CARP definition? Can they be shared by different IP addresses on the load balancer pair? That is, can they all be labelled "vhid=1" or is CARP limited to 256 IP addresses, each of which has to be a /32 (see above).

All the examples in the FreeBSD manual use a different vhid for each IP address but doesn't explain why.

a. If two addresses (aliases) share the same vhid, will that mean they fail over together always? (That might be a good thing for me). 
b. Will it reduce "are you alive?" network traffic between the CARP cluster to have one vhid?
c. Will bad things happen if I share vhids?


Thanks
Ari


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Aristedes Maniatis
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