Automate multiple subnet creation using SubnetPool¶

Operators of Mirantis Container Cloud for on-demand self-service Kubernetes deployments will want their users to create networks without extensive knowledge about network topology or IP addresses. For that purpose, the Operator can prepare L2 network templates in advance for users to assign these templates to machines in their clusters.

The Operator can ensure that the users’ clusters have separate IP address spaces using the SubnetPool resource.

SubnetPool allows for automatic creation of Subnet objects that will consume blocks from the parent SubnetPool CIDR IP address range. The SubnetPool blockSize setting defines the IP address block size to allocate to each child Subnet. SubnetPool has a global scope, so any SubnetPool can be used to create the Subnet objects for any namespace and for any cluster.

You can use the SubnetPool resource in the L2Template resources to automatically allocate IP addresses from an appropriate IP range that corresponds to a specific cluster, or create a Subnet resource if it does not exist yet. This way, every cluster will use subnets that do not overlap with other clusters.

To automate multiple subnet creation using SubnetPool:

Log in to a local machine where your management cluster kubeconfig is located and where kubectl is installed.

Note

The management cluster kubeconfig is created during the last stage of the management cluster bootstrap.
Create the subnetpool.yaml file with a number of subnet pools:

Note

You can define either or both subnets and subnet pools, depending on the use case. A single L2 template can use either or both subnets and subnet pools.
```
kubectl --kubeconfig <pathToManagementClusterKubeconfig> apply -f <SubnetFileName.yaml>
```
Note

In the command above and in the steps below, substitute the parameters enclosed in angle brackets with the corresponding values.

Example of a subnetpool.yaml file:
```
apiVersion: ipam.mirantis.com/v1alpha1
kind: SubnetPool
metadata:
  name: kaas-mgmt
  namespace: default
  labels:
    kaas.mirantis.com/provider: baremetal
    kaas.mirantis.com/region: region-one
spec:
  cidr: 10.10.0.0/16
  blockSize: /25
  nameservers:
  - 172.18.176.6
  gatewayPolicy: first
```
For the specification fields description of the SubnetPool object, see SubnetPool spec.
Verify that the subnet pool is successfully created:
```
kubectl get subnetpool kaas-mgmt -oyaml
```
In the system output, verify the status fields of the subnetpool.yaml file. For the status fields description of the SunbetPool object, see SubnetPool status.
Proceed to creating an L2 template for one or multiple managed clusters as described in Create L2 templates. In this procedure, select the exemplary L2 template for multiple subnets that contains the l3Layout section.

Caution

Using the l3Layout section, define all subnets that are used in the npTemplate section. Defining only part of subnets is not allowed.

If labelSelector is used in l3Layout, use any custom label name that differs from system names. This allows for easier cluster scaling in case of adding new subnets as described in Expand IP addresses capacity in an existing cluster.

Mirantis recommends using a unique label prefix such as user-defined/.