During installation, is it mandatory to have an internal/local DNS server when using your own FQDN and certificates?

Having an internal or local DNS server is not mandatory when using your own Fully Qualified Domain Name (FQDN) and certificates during installation. The primary requirement for a system like 3CX is that it can resolve the FQDN to the correct IP address. This resolution can be handled by public DNS servers if the FQDN is registered and the appropriate DNS records are configured, eliminating the need for an internal DNS server.

In many setups, especially if you are using cloud-hosted environments or simple installations, relying on external DNS can simplify the process. This setup is particularly beneficial in scenarios where an organization does not require complex DNS management or is managing only a few services.

Other considerations, such as dynamic DNS or specific configurations that necessitate local networks, can affect the decision to use an internal DNS server but do not make it an absolute requirement. Hence, using external DNS services can often suffice, making it clear why it is not deemed necessary to have an internal/local DNS server in every case.