Example of how to create a container to mirror Trusty and Xenial (complete with boot images for MAAS).

mirror.sh

CONTAINER=mirror

lxc launch ubuntu:x $CONTAINER

# Wait for the container to come online.
wait-for-systemd-container.sh $CONTAINER

# Ensure packages are up to date and install dependencies.
lxc exec $CONTAINER -- apt-get update
lxc exec $CONTAINER -- apt-get dist-upgrade -yu
lxc exec $CONTAINER -- apt-get install apt-mirror simplestreams ubuntu-cloudimage-keyring nginx aptly

# Import Ubuntu archive keys
lxc exec $CONTAINER -- sudo -Hu ubuntu /bin/bash -c \
    "gpg --no-default-keyring --keyring /usr/share/keyrings/ubuntu-archive-keyring.gpg --export | "`
   `"gpg --no-default-keyring --keyring trustedkeys.gpg --import"

# Import MAAS PPA keys
lxc exec $CONTAINER -- sudo -Hu ubuntu \
    gpg --no-default-keyring --keyring trustedkeys.gpg --keyserver keys.gnupg.net --recv-keys 5CFF1EA993EE8CC5
lxc exec $CONTAINER -- sudo -Hu ubuntu \
    gpg --no-default-keyring --keyring trustedkeys.gpg --keyserver keys.gnupg.net --recv-keys 04E7FDC5684D4A1C

# Create PPA mirrors
lxc exec $CONTAINER -- sudo -Hu ubuntu aptly mirror create maas-maintainers-experimental3-xenial http://ppa.launchpad.net/maas-maintainers/experimental3/ubuntu/ xenial || true
lxc exec $CONTAINER -- sudo -Hu ubuntu aptly mirror create maas-stable-trusty http://ppa.launchpad.net/maas/stable/ubuntu/ trusty || true
lxc exec $CONTAINER -- sudo -Hu ubuntu aptly mirror create maas-next-xenial http://ppa.launchpad.net/maas/next/ubuntu/ xenial || true
lxc exec $CONTAINER -- sudo -Hu ubuntu \
    aptly mirror update maas-maintainers-experimental3-xenial
lxc exec $CONTAINER -- sudo -Hu ubuntu \
    aptly mirror update maas-stable-trusty
lxc exec $CONTAINER -- sudo -Hu ubuntu \
    aptly mirror update maas-next-xenial


lxc exec $CONTAINER -- sudo -Hu ubuntu mkdir -p /home/ubuntu/var

cat > mirror.list << EOF
set base_path    /home/ubuntu
set mirror_path  $base_path/mirror
set skel_path    $base_path/skel
set var_path     $base_path/var
set cleanscript $var_path/clean.sh
set nthreads     20
set _tilde 0

deb-amd64 http://archive.ubuntu.com/ubuntu trusty main restricted universe multiverse
deb-amd64 http://archive.ubuntu.com/ubuntu trusty-security main restricted universe multiverse
deb-amd64 http://archive.ubuntu.com/ubuntu trusty-updates main restricted universe multiverse
deb-amd64 http://archive.ubuntu.com/ubuntu trusty-proposed main restricted universe multiverse
deb-amd64 http://archive.ubuntu.com/ubuntu trusty-backports main restricted universe multiverse

deb-amd64 http://archive.ubuntu.com/ubuntu xenial main restricted universe multiverse
deb-amd64 http://archive.ubuntu.com/ubuntu xenial-security main restricted universe multiverse
deb-amd64 http://archive.ubuntu.com/ubuntu xenial-updates main restricted universe multiverse
deb-amd64 http://archive.ubuntu.com/ubuntu xenial-proposed main restricted universe multiverse
deb-amd64 http://archive.ubuntu.com/ubuntu xenial-backports main restricted universe multiverse

deb-i386 http://archive.ubuntu.com/ubuntu trusty main restricted universe multiverse
deb-i386 http://archive.ubuntu.com/ubuntu trusty-security main restricted universe multiverse
deb-i386 http://archive.ubuntu.com/ubuntu trusty-updates main restricted universe multiverse
deb-i386 http://archive.ubuntu.com/ubuntu trusty-proposed main restricted universe multiverse
deb-i386 http://archive.ubuntu.com/ubuntu trusty-backports main restricted universe multiverse

deb-i386 http://archive.ubuntu.com/ubuntu xenial main restricted universe multiverse
deb-i386 http://archive.ubuntu.com/ubuntu xenial-security main restricted universe multiverse
deb-i386 http://archive.ubuntu.com/ubuntu xenial-updates main restricted universe multiverse
deb-i386 http://archive.ubuntu.com/ubuntu xenial-proposed main restricted universe multiverse
deb-i386 http://archive.ubuntu.com/ubuntu xenial-backports main restricted universe multiverse

# debian installer
deb-amd64 http://archive.ubuntu.com/ubuntu trusty main/debian-installer restricted/debian-installer multiverse/debian-installer universe/debian-installer
deb-amd64 http://archive.ubuntu.com/ubuntu trusty-security main/debian-installer restricted/debian-installer multiverse/debian-installer universe/debian-installer
deb-amd64 http://archive.ubuntu.com/ubuntu trusty-updates main/debian-installer restricted/debian-installer multiverse/debian-installer universe/debian-installer
deb-amd64 http://archive.ubuntu.com/ubuntu trusty-proposed main/debian-installer restricted/debian-installer multiverse/debian-installer universe/debian-installer
deb-amd64 http://archive.ubuntu.com/ubuntu trusty-backports main/debian-installer restricted/debian-installer multiverse/debian-installer universe/debian-installer

deb-amd64 http://archive.ubuntu.com/ubuntu xenial main/debian-installer restricted/debian-installer multiverse/debian-installer universe/debian-installer
deb-amd64 http://archive.ubuntu.com/ubuntu xenial-security main/debian-installer restricted/debian-installer multiverse/debian-installer universe/debian-installer
deb-amd64 http://archive.ubuntu.com/ubuntu xenial-updates main/debian-installer restricted/debian-installer multiverse/debian-installer universe/debian-installer
deb-amd64 http://archive.ubuntu.com/ubuntu xenial-proposed main/debian-installer restricted/debian-installer multiverse/debian-installer universe/debian-installer
deb-amd64 http://archive.ubuntu.com/ubuntu xenial-backports main/debian-installer restricted/debian-installer multiverse/debian-installer universe/debian-installer

deb-i386 http://archive.ubuntu.com/ubuntu trusty main/debian-installer restricted/debian-installer multiverse/debian-installer universe/debian-installer
deb-i386 http://archive.ubuntu.com/ubuntu trusty-security main/debian-installer restricted/debian-installer multiverse/debian-installer universe/debian-installer
deb-i386 http://archive.ubuntu.com/ubuntu trusty-updates main/debian-installer restricted/debian-installer multiverse/debian-installer universe/debian-installer
deb-i386 http://archive.ubuntu.com/ubuntu trusty-proposed main/debian-installer restricted/debian-installer multiverse/debian-installer universe/debian-installer
deb-i386 http://archive.ubuntu.com/ubuntu trusty-backports main/debian-installer restricted/debian-installer multiverse/debian-installer universe/debian-installer

deb-i386 http://archive.ubuntu.com/ubuntu xenial main/debian-installer restricted/debian-installer multiverse/debian-installer universe/debian-installer
deb-i386 http://archive.ubuntu.com/ubuntu xenial-security main/debian-installer restricted/debian-installer multiverse/debian-installer universe/debian-installer
deb-i386 http://archive.ubuntu.com/ubuntu xenial-updates main/debian-installer restricted/debian-installer multiverse/debian-installer universe/debian-installer
deb-i386 http://archive.ubuntu.com/ubuntu xenial-proposed main/debian-installer restricted/debian-installer multiverse/debian-installer universe/debian-installer
deb-i386 http://archive.ubuntu.com/ubuntu xenial-backports main/debian-installer restricted/debian-installer multiverse/debian-installer universe/debian-installer


deb-src http://archive.ubuntu.com/ubuntu trusty main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu trusty-security main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu trusty-updates main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu trusty-proposed main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu trusty-backports main restricted universe multiverse

deb-src http://archive.ubuntu.com/ubuntu xenial main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu xenial-security main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu xenial-updates main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu xenial-proposed main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu xenial-backports main restricted universe multiverse

clean http://archive.ubuntu.com/ubuntu
EOF

cat > postmirror.sh << EOF
#!/bin/bash

DISTS="trusty xenial"
ARCHIVE="archive.ubuntu.com"

for dist in $DISTS; do
    echo "Synchronizing $dist..."
    mkdir -p $HOME/extras/archive.ubuntu.com/ubuntu/dists/$dist/main/uefi
    rsync --recursive --times --links --hard-links --delete --delete-after --verbose \
        rsync://$ARCHIVE/ubuntu/dists/$dist/main/uefi/ \
        $HOME/extras/archive.ubuntu.com/ubuntu/dists/$dist/main/uefi
done

# Note: this requires /var/www/html to be owned by the user performing the mirror
cd /var/www/html
rm -rf ubuntu.working
echo "Linking archive..."
cp -al $HOME/mirror/archive.ubuntu.com/ubuntu ubuntu.working
for dist in $DISTS; do
    echo "Linking $dist..."
    rm -rf ubuntu.working/dists/$dist/main/uefi
    cp -al $HOME/extras/archive.ubuntu.com/ubuntu/dists/$dist/main/uefi \
        ubuntu.working/dists/$dist/main/uefi
done

mv ubuntu ubuntu.old
mv ubuntu.working ubuntu

rm -rf ubuntu.old

$HOME/var/clean.sh
EOF

chmod +x postmirror.sh

lxc file push mirror.list.amd64 $CONTAINER/etc/apt/mirror.list
lxc file push postmirror.sh $CONTAINER/home/ubuntu/var/postmirror.sh

lxc exec $CONTAINER -- chown ubuntu:ubuntu /var/www/html
lxc exec $CONTAINER -- sudo -Hu ubuntu apt-mirror

wait-for-systemd-container.sh

#!/usr/bin/env bash
# Copyright 2016 Canonical Ltd.  This software is licensed under the
# GNU Affero General Public License version 3 (see the file LICENSE).

# Exit immediately if a command exits with a non-zero status.
set -o errexit
# Treat unset variables as an error when substituting.
set -o nounset

CONTAINER=$1
if [ "$CONTAINER" == "" ]; then
    echo "Required argument: LXD container name"
    exit 1
fi

t=0
while [ "$(lxc exec $CONTAINER -- systemctl is-system-running | \
        sed 's/degraded/running/')" != "running" ]; do 
    sleep 0.1
    let t=$t+1 || true
done
let q=$t%4 || true
let t=$t/10 || true
echo "(waited $t.$q seconds for container startup)"