servers/roles/alpine/templates/interfaces.j2

auto lo
iface lo inet loopback

{% for iface in interfaces | selectattr('enabled') %}
auto {{ iface.name }}
iface {{ iface.name }} inet static
{% for ip in iface.ip_addresses %}
    address {{ ip.address }}
{% set subnet = ip.address | ipaddr('subnet') %}
{% set prefix = prefixes | selectattr('prefix', '==', subnet) | first %}
{% set gateway = prefix.custom_fields.gateway.address %}
{% if gateway is defined and gateway != ip.address %}
    gateway {{ gateway | ipaddr('address') }}
{% endif %}
{% endfor %}

{% endfor %}