High Availability on enterprise license and split DNS

[JohanFer]

Good day,
I am setting up HA on a Windows on Premise solution (V18 Enterprise) for a very large corporate and I need some inputs here please.
I will have the active server in DC-A and the passive server in DC-B each with its own IP address on the LAN. Each server will have its own public IP too. We have WAN links from multiple (28) sites where extensions registers from. This works well in single server setup many years now. I need some help with the split DNS and how to activate the active or standby when needed. Or just an overview of how things should work. Is there a way that DNS entry will automatically update when the standby server takes over? Or does the run of the scripts need to take place here?

Is this best practice or is there another way HA will work without any user interaction?

Any help here will be appreciated.

 

[SweetAction]

The answer depends on what DNS server your phones are querying to get the IP of the 3CX server.

If you are using a 3CX FQDN and resolving that FQDN externally only, it's automated as the public IP changes and 3CX updates it ~5 minutes. If you are resolving it internally (i.e. via RFC1918 address space), then whatever DNS server is doing that resolution will need to be updated. That's where the script running comes into place - you update the A record to point to the passive/failover server when needed.

 

[JohanFer]

The answer depends on what DNS server your phones are querying to get the IP of the 3CX server.

If you are using a 3CX FQDN and resolving that FQDN externally only, it's automated as the public IP changes and 3CX updates it ~5 minutes. If you are resolving it internally (i.e. via RFC1918 address space), then whatever DNS server is doing that resolution will need to be updated. That's where the script running comes into place - you update the A record to point to the passive/failover server when needed.

Thank you for your reply.
So I see there are multiple scripts for Windows. Do I edit and run ALL including shutdown the services and server, or is it only the DNSwindows script that need to be run? We will be using 3cx FQDN and the phones will use internal DNS which should resolve to the internal IP of the server. Are these scripts run on the 3cx server or DNS server?

 

[SweetAction]

Thank you for your reply.
So I see there are multiple scripts for Windows.

That's just example scripts, but you don't have to use the examples.

Do I edit and run ALL including shutdown the services and server, or is it only the DNSwindows script that need to be run?

That's really your call. What you need to accomplish is the FQDN resolving to the IP of the now active server. Everything from updating the IP in DNS to flushing any caches to making any changes to firewall and NAT rules is going to be specific to your environment and setup.

We will be using 3cx FQDN and the phones will use internal DNS which should resolve to the internal IP of the server.

Keep in mind the TTL for a FQDN from 3CX on an enterprise license is 5 minutes, so external users who use public DNS will not be able to connect if the public IP changes for up to that time. 6 hours for a PRO license.

Are these scripts run on the 3cx server or DNS server?

The 3CX server runs the scripts during the failover process, but you could have the 3CX server just do a powershell invoke-command against another server running scripts there

I'm going to be honest here, a better way of doing HA with 3CX is to ignore their failover options and make your 3CX server (which hopefully is a VM) highly available. You skip all of this and more as 3CX only "syncs" data once a day so you will lose some data (chats, call logs, etc) during an event. It's also going to be faster, provided it's done correctly.

 

[JohanFer]

That's just example scripts, but you don't have to use the examples.


That's really your call. What you need to accomplish is the FQDN resolving to the IP of the now active server. Everything from updating the IP in DNS to flushing any caches to making any changes to firewall and NAT rules is going to be specific to your environment and setup.


Keep in mind the TTL for a FQDN from 3CX on an enterprise license is 5 minutes, so external users who use public DNS will not be able to connect if the public IP changes for up to that time. 6 hours for a PRO license.


The 3CX server runs the scripts during the failover process, but you could have the 3CX server just do a powershell invoke-command against another server running scripts there

I'm going to be honest here, a better way of doing HA with 3CX is to ignore their failover options and make your 3CX server (which hopefully is a VM) highly available. You skip all of this and more as 3CX only "syncs" data once a day so you will lose some data (chats, call logs, etc) during an event. It's also going to be faster, provided it's done correctly.

Thank you for your detailed reply, appreciated.