Migrating dhcpd from a "single" server to "failover peer" setup

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Migrating dhcpd from a "single" server to "failover peer" setup

Danny Kulchinsky
Hello Everyone!

We are running for a while ISC DHCP (v4.2.5) on a single linux server and we would like to migrate it a highly available setup using "failover peer".

It is not very clear to me what would be the imapct of adding the failover peer configuration into an exisiting systems with leases that we obvisouly can't lose, I'm hoping that the system will perform the necessary changes but I don't feel confident about this.

Also, our ranges are defined under subnet and it is my understanding that these should be defined under pools where the "failover peer" is to be configured, is that correct? so, I guess same question here - can we move the ranges to "pools" without affecting any of the lease data?

Here's a subnet example in our setup:

subnet xxx.xxx.68.0 netmask 255.255.254.0 {
  range  xx.xxx.68.50 xx.xxx.68.150;
  range  xx.xxx.69.50 xx.xxx.69.200;
  option routers xx.xxx.68.1;
  option subnet-mask 255.255.254.0;
  option broadcast-address xx.xxx.69.255;
  option domain-search "<domain a>", "<domain b>", "<domain c>";
  option domain-name-servers xx.xxx.64.6, xx.xxx.64.7;
  default-lease-time 2592000;
  max-lease-time 10368000;
}

Can we just change it to:

subnet xxx.xxx.68.0 netmask 255.255.254.0 {
  pool {
    range  xx.xxx.68.50 xx.xxx.68.150;
    range  xx.xxx.69.50 xx.xxx.69.200;
    }
  }
  option routers  xx.xxx.68.1;
  option subnet-mask 255.255.254.0;
  option broadcast-address xx.xxx.69.255;
  option domain-search "<domain a>", "<domain b>", "<domain c>";
  option domain-name-servers xx.xxx.64.6, xx.xxx.64.7;
  default-lease-time 2592000;
  max-lease-time 10368000;
}



I couldn't find anything in the documenation that describes how to setup "failover peer" in a pre-exisiting server with leases, so any pointers would be highly welcome.


Thanks!
Danny

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Re: Migrating dhcpd from a "single" server to "failover peer" setup

Simon Hobson
Danny Kulchinsky <[hidden email]> wrote:

> It is not very clear to me what would be the imapct of adding the failover peer configuration into an exisiting systems with leases that we obvisouly can't lose, I'm hoping that the system will perform the necessary changes but I don't feel confident about this.

Yes, you just need to add the failover setup and the servers will automagically sync the existing leases to the new server. AIUI, the existing active leases will be "owned" by the original server, and any free addresses will be shared between the two servers.

> Also, our ranges are defined under subnet and it is my understanding that these should be defined under pools where the "failover peer" is to be configured, is that correct? so, I guess same question here - can we move the ranges to "pools" without affecting any of the lease data?

Yes.

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Re: Migrating dhcpd from a "single" server to "failover peer" setup

Danny Kulchinsky
Thank you Simon, this is very encouraging!

We are going to start by moving the ranges into pools and next step would be to establish the failover peer.


If you have any tips, let me know :)

Regards,
Danny

On 6 March 2018 at 08:07, Simon Hobson <[hidden email]> wrote:
Danny Kulchinsky <[hidden email]> wrote:

> It is not very clear to me what would be the imapct of adding the failover peer configuration into an exisiting systems with leases that we obvisouly can't lose, I'm hoping that the system will perform the necessary changes but I don't feel confident about this.

Yes, you just need to add the failover setup and the servers will automagically sync the existing leases to the new server. AIUI, the existing active leases will be "owned" by the original server, and any free addresses will be shared between the two servers.

> Also, our ranges are defined under subnet and it is my understanding that these should be defined under pools where the "failover peer" is to be configured, is that correct? so, I guess same question here - can we move the ranges to "pools" without affecting any of the lease data?

Yes.

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