resources.kube_master_eth0.properties.fixed_ips[0].subnet: Error validating value '': Unable to find subnet with name or id ''

[Felipe Reyes]

[Impact]

When creating a new "cluster" based from a "cluster template" that did NOT define the "Fixed Network" and "Fixed Subnet" fields, the cluster creation fails because it couldn't find a subnet for it, this is because the cluster object has its "fixed subnet" property set to `None`.

[Environment]

Focal Ussuri

[Test Case]

1. Create a new cluster template WITHOUT a fixed network/subnet set.
openstack coe cluster template create k8s-cluster-template \
    --image fedora-coreos-32 \
    --keypair testkey \
    --external-network ext_net \
    --flavor m1.small \
    --network-driver flannel \
    --coe kubernetes

2. Create a new cluster using the template previously created and select an existing network

openstack coe cluster create \
    --cluster-template k8s-cluster-template \
    --timeout 120 \
    --fixed-network private \
    k8scluster

Expected result

The cluster gets created

Actual result:

The cluster creation fails with the following error:

$ openstack coe cluster show k8scluster -f json -c faults | jq -r '.'
{
  "faults": {
    "default-master": "Resource CREATE failed: resources[0]: resources.kube_masters.Property error: resources.kube_master_eth0.properties.fixed_ips[0].subnet: Error validating value '': Unable to find subnet with name or id ''",
    "default-worker": "Resource CREATE failed: resources[0]: resources.kube_masters.Property error: resources.kube_master_eth0.properties.fixed_ips[0].subnet: Error validating value '': Unable to find subnet with name or id ''"
  }
}

[Felipe Reyes (freyes)]

Marking as duplicate of 2038109 since they share the same root cause.