installer/docs/user/openstack/deploy_dual_stack_cluster.md

# Creating a dual-stack cluster on OpenStack

## Table of Contents

- [Prerequisites](#prerequisites)
- [Creating DualStack Networks for the cluster](#creating-dualstack-networks-for-the-cluster)
- [Creating DualStack API and Ingress VIPs Ports for the cluster](#creating-dualstack-api-and-ingress-vips-ports-for-the-cluster)
- [Deploy OpenShift](#deploy-openshift)

## Prerequisites

* Installation with dual-stack is only allowed when using one OpenStack network with one IPv4 and IPv6 subnet.
* API and Ingress VIPs ports needs to pre-created by the user and the addresses specified in the `install-config.yaml`.
* Add the IPv6 Subnet to a neutron router to provide router advertisements.
* The dualstack network MTU must accommodate the minimum MTU for IPv6, which is 1280, and OVN-Kubernetes encapsulation overhead, which is 100.

Additional prerequisites are listed at the [OpenStack Platform Customization docs](./customization.md)

**Note**: Converting a IPv4 single-stack cluster to a dual-network cluster network is not supported by OpenStack.

## Creating Dual-Stack Networks for the cluster

You must create one network and add one IPv4 subnet and another IPv6 subnet with either slaac, stateless or stateful modes. Here is an example:

```sh
$ openstack network create --project <project-name> --share --external --provider-physical-network <physical-network> --provider-network-type flat dualstack
$ openstack subnet create --project <project-name> subnet-v4 --subnet-range 192.168.25.0/24 --dhcp --dns-nameserver <nameserver> --network dualstack
$ openstack subnet create --project <project-name> subnet-v6 --subnet-range fd2e:6f44:5dd8:c956::/64 --dhcp  --network dualstack --ip-version 6 --ipv6-ra-mode slaac --ipv6-address-mode slaac
```

Given the above example uses a provider network, this network can be added to the router external gateway to enable external connectivity and router advertisements with the following command:
```sh
$ openstack router set --external-gateway dualstack <router-id>
```

**Note**: Any additional IPv6 Subnet that is used in the OpenShift cluster, should be added to a neutron router to provide router advertisements.

## Creating Dual-Stack API and Ingress VIPs Ports for the cluster

You must create the API and Ingress VIPs Ports with the following commands:

```sh
$ openstack port create api --network dualstack
$ openstack port create ingress --network dualstack
```

## Deploy OpenShift

Now that the Networking resources are pre-created you can deploy OpenShift. Here is an example of `install-config.yaml`:

```yaml
apiVersion: v1
baseDomain: mydomain.test
compute:
- name: worker
  platform:
    openstack:
      type: m1.xlarge
  replicas: 3
controlPlane:
  name: master
  platform:
    openstack:
      type: m1.xlarge
  replicas: 3
metadata:
  name: mycluster
networking:
  machineNetwork:
  - cidr: "192.168.25.0/24"
  - cidr: "fd2e:6f44:5dd8:c956::/64"
  clusterNetwork:
  - cidr: 10.128.0.0/14
    hostPrefix: 23
  - cidr: fd01::/48
    hostPrefix: 64
  serviceNetwork:
  - 172.30.0.0/16
  - fd02::/112
platform:
  openstack:
    ingressVIPs: ['192.168.25.79', 'fd2e:6f44:5dd8:c956:f816:3eff:fef1:1bad']
    apiVIPs: ['192.168.25.199', 'fd2e:6f44:5dd8:c956:f816:3eff:fe78:cf36']
    controlPlanePort:
      fixedIPs:
      - subnet:
          name: subnet-v4
      - subnet:
          name: subnet-v6
      network:
        name: dualstack

```
There are important things to note:

The subnets under `platform.openstack.controlPlanePort.fixedIPs` can contain both id or name. The same applies to the network `platform.openstack.controlPlanePort.network`.