On Prem Failover with Enterprise License - DNS Question

[amir_]

We have a primary Site A where our Production 3CX VM is located. We are using the 3CX provided FQDN. In the 3CX failover mechanism, this server will be our "Active" server. We intend to build our "passive" server at our Site B - which has it's own Internet connection and public IP address space that differs from Site A.

The 3CX documentation here only provides detailed instructions for "3CX cloud PBXs":
https://www.3cx.com/docs/failover/

From that link:

Before configuring or enabling 3CX failover on your 2 servers, the 3CX installations need to conform to these requirements.
1. Two (2) 3CX cloud PBXs each with its own public IP, both installed with identical settings, including FQDN, SSL Certificate, SIP, Tunnel, web server ports and web server type.

Externally, I will map our SIP Telephony Trunks to the 3CX FQDN and with our Enterprise license, it is my understanding that the DNS TTL is 5 minutes and we can deal with that. The SIP Trunks will pick up the public IP change after the TTL and talk to our "passive" 3CX VM at the secondary site.

But what about Internal phones? Do I simply modify my internal DNS to map to the "passive" 3CX VM and the reboot the phones?

Thanks,

Amir

 

[Charles_3CX]

I can't speak for the provider being able to route calls based on FQDN but in regards to the question regarding the phones, essentially yes, internally, phones will connect to whichever A record is set in the internal DNS for the FQDN that is specified under the extensions settings > Phone provisioning tab. If using a single 3cx FQDN both internally and externally you can configure Split DNS for the 3cx FQDN internally, see this guide:
https://www.3cx.com/docs/creating-fqdn-split-dns/. In the upcoming version 18 the new feature called 'DNS Helper service', will also eliminate the need to configure DNS internally.

 

[amir_]

Perfect. Thank you. Is there a hard requirement that the specs of my "passive" 3CX VM be identical to the specs of the "active" 3CX VM?

 

[Charles_3CX]

The 3cx failover is designed so that the passive server will take over the role of the Active server in the event that the active server becomes unavailable, so to provide basic telephony needs until the active is back online and failed back to. It's a good idea, therefore, to have both machines configured with the same specification to avoid issues that may occur due to not having at least the minimum requirements as per our recommendations guide: https://www.3cx.com/docs/recommended-hardware-specifications-for-3cx/.

 

[amir_]

Thanks - we over built the VM for the active side - so what I don't want to do is carve out the same specs that we will likely never use for the passive side.

 

[cobaltit]

So 3CX does no checking of anything other than the passive monitoring the active. It doesn't care about what you do for DNS, specs of the machine, etc. DNS is handled however you decide to handle it, but the example scripts for updating DNS should give you an idea of what to do there. For the machine specs, as Chris said, you just need enough resources to run 3CX. So if your current VM is overbuilt, then you can have less on the passive. But if it's a VM on the passive side, it should be easy enough to increase resources as needed. Such is the beauty of VMs.

 

[amir_]

Thank you sir.