OpenWrt as Docker container host

As of OpenWrt 20.xx release (or snapshot images), OpenWrt can be used as Docker host at least on x86_64 (PC/server) architecture.

There are two main ways to use Docker as a host, install Docker Community Edition, or use native OpenWrt tools that support Docker container specification.

In any case, you will probably need to set up storage first as a place to store the containers and data.

install docker-ce package for the commandline tools
install luci-app-dockerman package to get a control panel for docker containers in Luci

Procd init system now supports Open Container Initiative Runtime Specification, extending its slim containers ('ujail') capability.
The uxc command line tool handles the basic operations on containers as defined by the spec.
This allows to use it as a drop-in replacement for Docker's 'runc' (or 'crun') on OpenWrt hosts with a significantly reduced footprint.

opkg install kmod-veth uxc ujail-console

uci batch <<EOF
set network.veth0=device
set network.veth0.type='veth'
set network.veth0.name='vhost0'
set network.veth0.peer_name='virt0'
add_list network.lan.ifname='vhost0'
set network.virt0=interface
set network.virt0.ifname='virt0'
set network.virt0.proto='none'
# set proto='none' assuming DHCP client inside container
# use 'static' otherwise and also set ipaddr, gateway and dns
set network.virt0.jail='container1'
set network.virt0.jail_ifname='host0'
commit network
EOF

(assuming OCI run-time bundle with config.json in /mnt/sda3/debian)

uxc create container1 /mnt/sda3/debian true
uxc start container1

uxc list
uxc state container

If the container uses a stdio console, you can attach it using

ujail-console -c container1

(there is no buffer, so if you like to see the complete bootlog of a container, make sure to attach a console after the 'create' call but before starting it)