DNS settings affect whether SDDC Manager and the VCF Installer can reliably reach external services, updates, and managed components. Therefore, a change should not only be executed from the console, but should be prepared in a traceable manner and then verified. Depending on the situation, it may be necessary during deployment of the VCF Installer or as part of VCF Conversion to adjust the DNS servers of the VCF Installer afterwards.
The available commands differ by version. For SDDC Manager 4.x as well as 5.1 or older, vami_set_dns is used. For SDDC Manager 5.2 this approach is no longer intended; instead, a separate guide for DNS configuration is required. SDDC Manager 9.0 and the VCF Installer 9.0, on the other hand, use nmctl.
Before making a change, it is advisable to take an offline snapshot of the SDDC-Manager VM as a safety measure. This provides a recovery point in case of problems. Additionally, the intended primary and secondary DNS servers, as well as optionally the domain and search path, should be defined in advance.
For older SDDC-Manager versions, log in via SSH using the vcf account. Afterwards, the DNS system can be updated with the following syntax:
sudo /opt/vmware/share/vami/vami_set_dns DNS_Server_1 DNS_Server_2
The placeholders DNS_Server_1 and DNS_Server_2 are replaced by the respective IP addresses. If the domain and search path also need to be changed, the command sequence can be extended:
sudo /opt/vmware/share/vami/vami_set_dns -d domain -s searchpath DNS_Server_1 DNS_Server_2
Here domain stands for the desired DNS domain name and searchpath for the search path. The IP addresses of the DNS servers remain unchanged as the last parameters.
For SDDC Manager 9.0 or the VCF Installer 9.0, first log in via SSH and then open a root environment:
su -
Afterwards, the network interface configuration can be updated. In the source, eth0 is used as an example:
nmctl set-dns dev eth0 dns DNS_Server_1,DNS_Server_2
The interface designation should be adjusted to match the actual network configuration. The DNS servers are specified here separated by commas. After the change, nmctl show_dns can be used to query the configured servers directly. Additionally, cat /etc/resolv.conf shows which DNS servers are present in the resolver configuration.
To ensure the changes take full effect, the network name resolution service can be restarted:
sudo systemctl restart systemd-resolved.service
Afterwards, both nmctl show_dns and the check of /etc/resolv.conf should be run again. For older SDDC-Manager versions, /opt/vmware/share/vami/vami_dns can also be used for verification.
The configuration should not be judged solely by a successful command. It is sensible to perform a brief functional test with a DNS resolution and, if applicable, access to a known external service. This way you can determine whether not only the configuration files were changed, but name resolution actually works in runtime.
References
Configure/Update DNS Server IP Address in SDDC Manager or the VCF Installer through Command Line