I was unable to get the static IP address configuration to work using the network section of the cloudinit cloud configs. So, I wrote the ifcfg file directly using the #cloud-config section. For example:

#cloud-config
write_files:
- content: |
    # Cloudinit icfg-eth0 file (centos/redhat format)

    BOOTPROTO=STATIC
    DEVICE=eth0
    ONBOOT=yes
    TYPE=Ethernet
    USERCTL=no
    IPADDR=192.168.50.50
    NETMASK=255.255.255.0
    GATEWAY=192.168.50.1
    DNS1=8.8.8.8
    DNS2=8.8.4.4
  path: /etc/sysconfig/network-scripts/ifcfg-eth0

Another user had this question in the old forums, and I wanted to post an alternate solution to the echo "long string of config" > file method mentioned there.

https://xen-orchestra.com/forum/topic/1041/cloud-init-question-for-static-ip-adresse