baremetal: expand baremetal IPI docs to include customizations

The platform now has a bunch of optional possible customizations, this
expands the documentation to follow the other platforms by including a
customization.md that details each of the options and why you might want
to use them.

docs/user/customization.md

@@ -49,6 +49,7 @@ The following `install-config.yaml` properties are available:
         The default is 172.30.0.0/16.
 * `platform` (required object): The configuration for the specific platform upon which to perform the installation.
     * `aws` (optional object): [AWS-specific properties](aws/customization.md#cluster-scoped-properties).
+    * `baremetal` (optional object): [Baremetal IPI-specific properties](metal/ipi/customization.md).
     * `azure` (optional object): [Azure-specific properties](azure/customization.md#cluster-scoped-properties).
     * `openstack` (optional object): [OpenStack-specific properties](openstack/customization.md#cluster-scoped-properties).
     * `vsphere` (optional object): [vSphere-specific properties](vsphere/customization.md#cluster-scoped-properties).

docs/user/metal/install_ipi.md

@@ -89,7 +89,8 @@ containing all of the details of the bare metal hosts to be provisioned.
 
 The `install-config.yaml` file requires some additional details.  Most of the
 information is teaching the installer and the resulting cluster enough about
-the available hardware so that it is able to fully manage it.
+the available hardware so that it is able to fully manage it. There are
+[additional customizations](ipi/customization.md) possible.
 
 Here is an example `install-config.yaml` with the required `baremetal` platform
 details.

docs/user/metal/ipi/customization.md

@@ -0,0 +1,68 @@
+# Bare Metal Platform Customization
+
+## Image Overrides
+
+When doing a disconnected installation, the baremetal platform has the
+additional requirement that we have locations to download the RHCOS
+images. The installer downloads these from a location described in
+[/data/data/rhcos.json](/data/data/rhcos.json), but they can be
+overriden to point to a local mirror.
+
+```yaml
+platform:
+  baremetal:
+      bootstrapOSImage: http://mirror.example.com/images/rhcos-43.81.201912131630.0-qemu.x86_64.qcow2.gz?sha256=f40e826ac4a6c5c073416a7bc0039ec8726a338885d2031e7607cec8783e580e
+      clusterOSImage: http://mirror.example.com/images/rhcos-43.81.201912131630.0-openstack.x86_64.qcow2.gz?sha256=ffebbd68e8a1f2a245ca19522c16c86f67f9ac8e4e0c1f0a812b068b16f7265d
+```
+
+## Networking customization
+
+By default, the baremetal IPI environment uses a provisioning network of
+`172.22.0.0/24`, picks the 2nd and 3rd address of that subnet for the
+bootstrap and cluster provisioning IP's, and operates an internal DHCP
+and TFTP server in the cluster to support provisioning. Much of this can
+be customized.
+
+### Custom provisioning network
+
+To use a different network range, a user may set the
+`provisioningNetworkCIDR` option. If they wish to use a different
+we will pick the 2nd and 3rd addresses in that subnet.
+
+
+```yaml
+platform:
+  baremetal:
+    provisioningNetworkCIDR: 172.23.0.0/16
+    bootstrapProvisioningIP: 172.23.0.2
+    provisioningHostIP: 172.23.0.3
+```
+
+### Custom DHCP range
+
+By default, the installer picks a range from the 10th to 100th
+addresses. To use a different range, specify this using the
+provisioingDHCPRange option in the baremetal platform. This should be a
+comma-separated list indicating the start and end range.
+
+```yaml
+platform:
+  baremetal:
+    provisioningDHCPRange: "172.23.0.10,172.23.0.100"
+```
+
+
+### External DHCP
+
+If you would prefer to use an external DHCP server, you can specify
+provisioningDHCPExternal, in which case the cluster will only run TFTP.
+When using PXE boot for the control plane and workers, your DHCP server
+needs to specify the next-server as `bootstrapProvisioningIP` for the
+control plane, and `provisioningHostIP` for the workers.
+
+```yaml
+platform:
+  baremetal:
+    provisioningDHCPExternal: true
+```
+