Mirantis Container Cloud (MCC) becomes part of Mirantis OpenStack for Kubernetes (MOSK)!

Starting with MOSK 25.2, the MOSK documentation set covers all product layers, including MOSK management (formerly MCC). This means everything you need is in one place. The separate MCC documentation site will be retired, so please update your bookmarks for continued easy access to the latest content.

Adjust DNS servers for subnets¶

Use this procedure if the subnets_without_dns_nameservers_check fails in the pre-migration checks. This check indicates that some subnets are missing DNS nameserver configuration. Configuring DNS servers is required to ensure that instances can resolve domain names after migration from Open vSwitch (OVS) to Open Virtual Network (OVN).

To configure DNS servers for affected subnets:

Obtain the list of addresses of default DNS nameservers from the OpenStackDeployment object:
```
kubectl -n openstack get osdpl osh-dev \
  -o jsonpath='{.spec.features.neutron.dns_servers}'
```
Verify that these DNS servers are reachable and can resolve DNS queries from instances.

Update the DNS servers for affected subnets by logging in to the keystone-client pod and running:

IFS=',';
subnets=$(cat /tmp/preflight_checks.json | \
  jq -c .subnets_without_dns_nameservers_check.violations | \
  tr -d [] | tr -d \")
for s in $subnets; do
  openstack subnet set --dns-nameserver <DNS0> \
  --dns-nameserver <DNS1> $s; done

Replace <DNS0> and <DNS1> with the DNS servers obtained in the previous step.

Wait for the DHCP renewal interval to pass so that the new DNS settings are propagated to all instances.

Note

Setting of the DHCP renewal interval (T1) is described in Adjust MTU for VXLAN tenant networks.
Log in to a few instances and verify that the DNS server settings were updated. For example, on systemd-based operating systems, you can check the current DNS servers using:
```
systemd-resolve --status
```

After completing this procedure, all affected subnets will have explicitly configured DNS servers, and instances will use these servers for name resolution.