start multipass docker.

start-docker.sh

#!/usr/bin/env bash


export DOCKER_HOST=ssh://ubuntu@docker.local
export DOCKER_HOST=tcp://docker.local
multipass set client.primary-name=docker
function start-docker() {
    local SSH_KEY="id_$RANDOM"
    local PUBLIC_SSH_KEY="${SSH_KEY}.pub"
    ssh-keygen -b 2048 -t rsa -f "$SSH_KEY" -P ""
    ssh-add "${SSH_KEY}"
    cat <<-EOF | tee /tmp/user-conf.yml
---
users:
  - name: ubuntu
    sudo: ALL=(ALL) NOPASSWD:ALL
    ssh-authorized-keys:
      - $(cat ${PUBLIC_SSH_KEY}) 
package_update: true
packages:
  - docker
  - avahi-daemon
  - apt-transport-https
  - ca-certificates
  - curl
  - gnupg
  - lsb-release
write_files:   # Allows us to mount docker directly without ssh magics..
  - path: /etc/systemd/system/docker.service.d/docker.conf 
    content:
          |
            [Service]
            ExecStart=
            ExecStart=/usr/bin/dockerd 
  - path: /etc/docker/daemon.json
    content:
          |
            {
               "insecure-registries": [],
               "hosts": ["unix:///var/run/docker.sock","tcp://0.0.0.0:2375"],
               "features": { "buildkit" : true }
            }
runcmd:
 - sudo curl -fsSL https://get.docker.com | sudo bash
 - sudo systemctl enable docker
 - sudo systemctl enable -s HUP ssh
 - sudo groupadd docker
 - sudo usermod -aG docker ubuntu
EOF
    multipass launch -c 2 -m 2G -d 40G -n docker 20.04 --cloud-init /tmp/user-conf.yml
    echo "done"
}

The docker.conf and daemon.json overrides the original ExecStart Value so that I can specify the hosts myself in a simpler way in json.