How to add br_netfilter to an LXD container
You need to create or use an existing profile that enables the br_netfilter module
$ lxc profile create mod_br_netfilter
$ lxc profile set mod_br_netfilter linux.kernel_modules br_netfilter
$ lxc profile show mod_br_netfilter
name: mod_br_netfilter
config:
linux.kernel_modules: br_netfilter
description: ""
devices: {}
$ lxc launch ubuntu:latest YOURcontainer -p default -p mod_br_netfilter
############ To apply to an existing Instance #####################
$ lxc profile apply YOURcontainer default, mod_br_netfilter
$ lxc restart YOURcontainer
Alternatively you can edit any profile you already use to support this kernel module
$ lxc profile edit default
edit the config
section to add the configuration key
linux.kernel_modules: br_netfilter