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

Fri Nov 18 08:23:59 UTC 2022

Many thanks for these interesting hints!
A last question then: how do you notify KEA processes (kea-dhcp4, kea-dhcp6) in case you modify any of you json files ? with a "reload" command ?
Thanks,
Veronique
________________________________
From: Dan Oachs <doachs at gac.edu>
Sent: Thursday, November 17, 2022 8:36 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

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<mailto: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<mailto:doachs at gac.edu>>
Sent: Thursday, November 17, 2022 4:20 PM
To: Veronique Lefebure <Veronique.Lefebure at cern.ch<mailto:Veronique.Lefebure at cern.ch>>
Cc: kea-users at lists.isc.org<mailto:kea-users at lists.isc.org> <kea-users at lists.isc.org<mailto: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<mailto: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<mailto:doachs at gac.edu>>
Sent: Wednesday, November 16, 2022 6:31 PM
To: Veronique Lefebure <Veronique.Lefebure at cern.ch<mailto:Veronique.Lefebure at cern.ch>>
Cc: kea-users at lists.isc.org<mailto:kea-users at lists.isc.org> <kea-users at lists.isc.org<mailto: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<mailto: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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