[Kea-users] Kea implementation planning

[Jason Guy]

Hi Ben,

Good questions, and like most other technology, the answer always starts
with "It depends..." :)
I will expand on what Francis said with some of my own thoughts and
decisions as I was implementing my setup.

1) The best thing about Kea is that the data can be stored in a separate
server running a database. This allows you to have a single server, or
multiple servers.

2) There are HA features coming in Kea, and that will hopefully make
multiple instances a lot easier to work with. Currently the thing to
understand is the server that offers the leas, is the server that has to
manage that lease. While the data is stored in the database, the state is
local to the server. As I understand it, the HA features will allow that
state to be shared between servers, meaning in the event of a failure, the
redundant server can pickup the management of the lease.

3) Assuming the server is physically on the same subnet (no dhcp relay),
both servers will act on the DHCP broadcast messages. To get around this,
you will put the DHCP servers behind an load balancer (like HA-proxy).

4) In the spirit of deploying microservices, it is best to separate each
service, and use the DHCP-DDNS to populate the DNS server with the DHCP
information.

In my deployment, I created everything as virtual machines to leverage the
HA redundancy of the compute servers as well. The Raspberry Pi's are a fine
choice, but I found VMs to be a lot easier to work with if I need to scale
things up (which I am working on now). The other decision I made was to use
PowerDNS because it also stores the data in a database, thus separating the
service from the data.

Hope this helps.
Jason




On Mon, Jan 15, 2018 at 3:50 AM, Francis Dupont <fdupont at isc.org> wrote:

> Ben Monroe writes:
> > 1)      Is it normal for a subnet to have a single DHCP instance or
> > multiples instances?
>
> => single
>
> > 2)      In the case that multiple DHCP servers exist on a the same
> subnet,
> > are the instances all active and load balanced? Or is only one active
> while
> > the others are inactive until some kind of failover occurs?
>
> => you can do both.
>
> > 3)      If multiple DHCP servers exist on the same subnet and are all
> > active, what is to prevent a client from receiving multiple DHCP
> responses?
>
> => nothing!
>
> > 4)      Is it normal to run both DNS and DHCP services on a single
> server?
> > Are there advantages to running DNS and DHCP on separate servers?
>
> => it is common but of course you get a single point of failure.
>
> > The answers to these questions will help in deciding whether I should
> > install Kea on the same server instances (Raspberry Pi 3) that are
> running
> > DNS (Bind), how many servers, or whether I should split them to dedicated
> > servers (likely also Raspberry Pi 3).
>
> => you have another choice: use a file or a database for leases and
> in the second case where to put the database server (same box than Kea
> or another box).
>
> Thanks
>
> Francis Dupont <fdupont at isc.org>
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