failover and loadbalance for relayed requests

[Gregory Sloop]

Just a note - it's not really "fail-over" but more load-balancing with the ability to handle the loss of one of the peers. [At least when *I* think if fail-over, I think of a server in stand-by, which isn't doing anything. Then when the primary active server fails, the "fail-over" comes up and fully takes over for the primary. And that's not the "fail-over" that ISC DHCPd does.]

I'm not knocking it at all - just that it's got some interesting nuance that can bite you.
Some of these potential pitfalls in peer/fail-over/load-balancing have been, at least partially, mitigated in versions 4.2.0+ [I think] and newer.

A search of the archives and release notes will help you find some of these.
[See: auto-partner-down, and the "rewind" feature also added in 4.2.0+ versions.]

Read the docs carefully - it's quite a bit more complex than you might think at first glance. Not terribly hard or difficult, but it may not function exactly as you'd imagined it to do. 
[Corner cases always bite you when you lease(t) {pun intended} expect.]

HTH

-Greg

L> Thanks Simon !!!

L> On 03/06/15 12:18, Simon Hobson wrote:
>> Leandro <ingrogger at gmail.com> wrote:

>>> I would like to ask for some documentation to read
>> start with "man dhcpd.conf"

>>> and also ask for the dhcp isc failover capabilities and recommendations.
>> You can have 2 (and no more than 2) servers in a failover pair per pool. You essentially clone the config file from the primary to the secondary - and add the relevant failover peer declarations.

>>> I imagine to setup two servers for instance with lease database sync and two ips configured on the relays ... is that possible ?
>> Yes, that's how it works

>>> how does iscp manage the leases db sync?
>> It's internal. When one server issues a lease, it notifies the other which updates it's local lease file.
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