How to create multiple Multipass Ubuntu instances with name resolution between them using a custom /etc/hosts file

append-to-etc-hosts-in-vm.sh

#!/bin/bash
#
# This script should run in a multipass VM.
# Take the hosts file that was written at creation and append it to /etc/hosts.
# This way, the hosts that we created can talk to each other by hostname.
#

# Errors are fatal
set -e

pushd $(dirname $0) > /dev/null

echo "# Adding to /etc/hosts..."

#
# Doing this with a here document because sudo won't otherwise work with redirection...
#
sudo bash << EOF
cat hosts >> /etc/hosts
EOF

start-multipass-instances

#!/bin/bash
#
# Spin up our multipass instances
#

# Errors are fatal
set -e

# How many hosts to create?
NUM=3

# Change to the directory where this script lives
pushd $(dirname $0) > /dev/null

#
# Parse our command line arguments
#
function parse_args() {

        while test "$1"
        do
                if test "$1" == "-h" -o "$1" == "--help"
                then
                        echo "! Syntax: $0 [ num_hosts ]"
                        exit 1
                else
                        NUM=$1
                fi
                shift
        done

} # End of parse_args()


#
# Delete a host
#
function delete_host() {

        local HOST=$1
        echo "# Deleting host ${HOST}..."
        multipass delete ${HOST} || true

} # End of delete_host()


#
# Create a host
#
function create_host() {

        local HOST=$1

        echo "# Creating host ${HOST}..."
        multipass launch -c 2 -n ${HOST} --cloud-init ./cloud-config.yml
        multipass mount . ${HOST}:/mnt

} # End of create_host()


#
# Create our hosts
#
function create_hosts() {
        
        for I in $(seq -f %02g ${NUM})
        do
                delete_host k8s-${I}
        done

        multipass purge

        for I in $(seq -f %02g ${NUM})
        do
                create_host k8s-${I}
        done

} # End of create_hosts()


#
# Create our hosts file to glue on to /etc/hosts
#
function create_hosts_file() {
        
        multipass list --format csv | awk '{FS=","; print $3 "\t" $1}' > hosts

        for I in $(seq -f %02g ${NUM})
        do
                local HOST="k8s-${I}"
                multipass exec ${HOST} /mnt/append-to-etc-hosts-in-vm.sh
        done
        

} # End of create_hosts_file()


parse_args $@
echo "# Creating ${NUM} k8s hosts..."
create_hosts
multipass list

create_hosts_file

echo "# Done!"