DNS
The RHOCP Version 4 installation program greatly simplifies the DNS requirements that are seen in previous RHOCP installations. All internal DNS resolution for the cluster, certificate validation, and bootstrapping is provided through a self-hosted, installer-controlled solution that uses the mDNS plugin for CoreDNS.
This solution was developed to perform DNS lookups based on discoverable information from mDNS.
This plug-in resolves both the etcd-NNN records and the _etcd-server-ssl._tcp.SRV
record. It is also able to resolve the name of the nodes.
With this solution, you do not need to add the IP addresses of the control plane nodes, compute nodes, and the bootstrap node, either manually or dynamically, to any form of public DNS. The RHOCP installation is entirely self-contained in this respect.
This reference architecture considers the use of the RHOCP installation program parameter `externalDNS` to allow the installer-built subnets to offer external DNS resolution to their instances.
DNS setup
The RHOCP on z/VM deployment has the following DNS requirements, both before and after installation:
- The installation host must be able to resolve the RHOCP API address.
- The bootstrap node must be able to resolve external, public domains.
More details can be found in the IBM Redbooks Red Hat OpenShift on IBM Z Installation Guide
- RHOCP API DNS
- The RHOCP API floating IP address needs to be in place for installing the cluster, and ensuring
the
api.<cluster name>.<base domain>address space resolves to it. - Application DNS
- A wildcard entry is required in your DNS for this IP to resolve the following naming structure:
*.apps.<cluster name>.<base domain>. - Bootstrap node
- The bootstrap node must be able to resolve external domain names directly. The RHOCP 4 installation program uses this name resolution to connect externally and retrieve the containers that are required to stand up the bootstrap cluster that is used to instantiate the production cluster. No other RHOCP nodes require this external resolution.