netboot.xyz/roles/netbootxyz/templates/menu/index.html.j2

#!ipxe
####       {{ boot_domain }} initial loader          
#### see https://netboot.xyz for more information
{% if bootloader_https_enabled | bool %}
set conn_type https
chain --autofree https://{{ boot_domain }}/menu.ipxe || echo HTTPS failed... attempting HTTP...
{% endif %}
{% if bootloader_http_enabled | bool %}
set conn_type http
chain --autofree http://{{ boot_domain }}/menu.ipxe || echo HTTP failed, localbooting...
{% endif %}