Description of problem:

During an OpenShift install every instance expects DNS resolution OOTB. 

This may not be the default condition in many customers as many want their tenants to add this when they create a private network. Simply, they don't want a global nameserver set.

Right now, the OCP 4.2 installer creates the tenant network WITHOUT any nameserver set

This functionality to create a nameserver on the those networks used be in the code at: https://github.com/openshift/installer/commit/e78dda8acbbe358d3a2d141005889ee55e7b74b6#diff-2e9ee288606583af9d7aff21a6a2cf81

But was removed.

The installer should allow clouds deployed without default nameservers made available OOTB to set a nameserver on the networks it creates. This could work like the reverted commited listed above, but should, ideally, be variablised.


Version-Release number of the following components:
 oc version
Client Version: version.Info{Major:"4", Minor:"2+", GitVersion:"v4.2.0", GitCommit:"2e9d4a117", GitTreeState:"clean", BuildDate:"2019-07-28T17:15:26Z", GoVersion:"go1.12.6", Compiler:"gc", Platform:"linux/amd64"}
Server Version: version.Info{Major:"1", Minor:"14+", GitVersion:"v1.14.0+463e263", GitCommit:"463e263", GitTreeState:"clean", BuildDate:"2019-07-30T02:08:56Z", GoVersion:"go1.12.5", Compiler:"gc", Platform:"linux/amd64"}
[stack@undercloud installer]$ bin/openshift-install version
bin/openshift-install unreleased-master-1456-gc998f555539fbf1e07a78bc5f55a20798c072d2a-dirty
built from commit c998f555539fbf1e07a78bc5f55a20798c072d2a
release image registry.svc.ci.openshift.org/origin/release:4.2


How reproducible:
Install with 4.2 installer.

Steps to Reproduce:
1. Install with version above
2. Private networks will be created without nameserver resolution
3.

Actual results:
Instances can't resolve and registry pulls will fail. The install will time out.

Expected results:
Install succeeds.

Additional info:

I am aware that to provide this type functionality to tenant networks OOTB you can set this with director by doing something like:

NeutronDhcpAgentDnsmasqDnsServers: 192.168.122.1

Pointing at a working nameserver.

This setting, from the docs, "allows dnsmasq_dns_servers to be configured for Neutron DHCP Agent with a new parameter (NeutronDhcpAgentDnsmasqDnsServers, default to [])."

Ref: https://docs.openstack.org/releasenotes/tripleo-heat-templates/ocata.html

Essentially this lets Neutron's DHCP act as a DNS server for all instances and provides it by default. 

But this is global setting and may not be desirable or even possible in many environments. For this reason I think the installer should allow customers to set DNS on the private subnets it builds.