[Kea-users] How to best update the KEA configuration on a HA hot-standby KEA setup

[Dan Oachs]

The great thing about Kea is that it is very flexible and you can make it
work in a wide variety of ways and find the setup that works best for your
situation.

In our case we have a hybrid setup.  The kea-dhcp4.conf file has all the
global settings, and we define the hosts-database for storing host
reservations.  We also break out all the subnet config into a separate
subnets.json file and have the main file include that.

We update the database directly from our own registration system, which is
not recommended, but works fo us.  We chose not to pay for the host
commands hook library that is required to use the api example you
mentioned.

I am pretty sure that you can do almost everything in the database that you
can do in the config file, but are only using the database to store the
host information.  I do see tables in the database that start with
dhcp4_client_class which would lead me to believe that you can do what you
want with the database configuration.

--Dan


On Thu, Nov 17, 2022 at 9:48 AM Veronique Lefebure <
Veronique.Lefebure at cern.ch> wrote:

> Thanks Dan!
>
>
> So you have a hybrid configuration ?
> What do you mean by "main configuration" ? Topology (shared-networks and
> subnets) in json file and host-reservations in a database ?
> Do you update the database using "reservation-add"  (
> https://kea.readthedocs.io/en/latest/api.html?highlight=host%20reservation#reservation-add )
> ?
>
> We have client classes with a test expression that depends on the mac
> addresses of the clients.
> Can these classes be stored in the database as well ?
>
> Thanks,
> Veronique
>
>
> ------------------------------
> *From:* Dan Oachs <doachs at gac.edu>
> *Sent:* Thursday, November 17, 2022 4:20 PM
> *To:* Veronique Lefebure <Veronique.Lefebure at cern.ch>
> *Cc:* kea-users at lists.isc.org <kea-users at lists.isc.org>
> *Subject:* Re: [Kea-users] How to best update the KEA configuration on a
> HA hot-standby KEA setup
>
> We also have all the main configuration in plain json files.  Like you, we
> require hosts on some of our networks to be registered.  Our registration
> system stores the MAC addresses in the Kea database.  For the past year or
> so, this has worked really well for us.
>
> I would highly suggest looking into storing the MAC addresses in a
> database so you don't need to reload kea for every change.  You don't need
> to use the database for anything else if you don't want to.   This can also
> be done without any of the extra hook libraries that cost money.
>
> --Dan
>
>
>
> On Thu, Nov 17, 2022 at 2:19 AM Veronique Lefebure <
> Veronique.Lefebure at cern.ch> wrote:
>
> Hi,
>
> We don't use any database for storing the KEA configuration: we use plain
> json configuration files.
> We need to update the configuration very regularly because we allow only
> known clients (pre-registered mac addresses), hence the list of
> host-reservations is quite volatile.
>
> Véronique
> ------------------------------
> *From:* Dan Oachs <doachs at gac.edu>
> *Sent:* Wednesday, November 16, 2022 6:31 PM
> *To:* Veronique Lefebure <Veronique.Lefebure at cern.ch>
> *Cc:* kea-users at lists.isc.org <kea-users at lists.isc.org>
> *Subject:* Re: [Kea-users] How to best update the KEA configuration on a
> HA hot-standby KEA setup
>
> I am curious why you are updating the config every 5 minutes.   We used to
> do that with our old DHCP server, but with Kea we moved to storing
> reservations in a database.  That way we rarely need to make changes to the
> actual Kea configuration that would necessitate a reload of the config.
>
> --Dan
>
>
> On Wed, Nov 16, 2022 at 10:27 AM Veronique Lefebure <
> Veronique.Lefebure at cern.ch> wrote:
>
> Hi,
>
> When running KEA on one single server, (no HA), and updating the KEA dhcp
> configuration file every 5 minute, using "config-set"
>
> https://kea.readthedocs.io/en/latest/arm/ctrl-channel.html?highlight=config-set#the-config-set-command
>  ,
> we can see that KEA does not reply to the DHCP requests during 30-35
> seconds while "config-set" is running.
>
> Is it expected ?
> If yes, if we add a second server in a HA hot-standby mode, can we expect
> it to answer to the DHCP requests while the first server is busy with
> config-set ?
> If yes, we need to update the second server asynchronously with respect to
> the first one, else they would both be busy with "config-set" at the same
> time.
>
> I would be interested to know how people are updating the KEA DHCP
> configuration in a HA hot-standby setup.
>
> Thanks,
> Veronique
>
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