Hi, here is a script we're toying with which starts an ephemeral
container based on an existing one, with an aufs read-write layer
on top. When the container shuts down, it disappears. This same
script should be trivial to extend to support use of overlayfs in
place of aufs. (It belongs in src/lxc/lxc-start-ephemeral.in, but
I have it sitting elsewhere so that it stands cleanly apart from
upstream code)
Thoughts?
Many thanks to Robert Collins for the original script.
================================================
#!/bin/bash
# This script runs up and removes an aufs layered lxc container.
#
# Usage: lxc-start-aufs BASECONTAINER (BINDMOUNT or --) [COMMAND [ARGS...]]
# BASECONTAINER should be the simple name of a container to layer on. This
# container probably shouldn't be running.
# BINDMOUNT is a path in the host environment to bind mount into the container
# - e.g. /home/username or some such.
# COMMAND and ARGS are the command and args to run in the container.
# If no BINDMOUNT is desired *and* a COMMAND is desired, provide -- as the
# BINDMOUNT.
# (C) Copyright Canonical 2011
# What lxc container to clone
LXC_BASE=""
# $2 is a path to bind mount e.g. /tmp/foo.
LXC_BIND=""
uniontype="aufs"
usage() {
echo "usage: lxc-start-ephemeral [-h] [-t type] [-b bdir] -o orig --
[COMMAND [ARGS...]]"
}
help() {
usage
echo
echo "Runs an ephemeral (one-off) container"
echo
echo "Options:"
echo "type : type of union fs to use. aufs by default"
echo " : Overlayfs and others will be possible one day"
echo "orig : name of the original container"
echo "bdir : directory to bind mount into container"
}
shortoptions='ht:b:o:'
longoptions='help,orig:,bdir:,type:'
getopt=$(getopt -o $shortoptions --longoptions $longoptions -- "$@")
if [ $? != 0 ]; then
usage
exit 1;
fi
eval set -- "$getopt"
while true; do
case "$1" in
-h|--help)
help
exit 1
;;
-t|--type)
shift
uniontype=$1
shift
if [ $uniontype != 'aufs' ]; then
echo "only aufs is supported"
fi
;;
-o|--orig)
shift
LXC_BASE=$1
shift
;;
-b|--bdir)
shift
LXC_BIND=$1
shift
;;
--)
shift
break;;
*)
echo $1
usage
exit 1
;;
esac
done
LXC_USER=`id -un`
# validation
if [ -z $LXC_BASE ]; then
echo "original container must be specified"
usage
exit 1
fi
if [ ! -d /var/lib/lxc/$LXC_BASE ] ; then
echo 'no such lxc container $LXC_BASE'
exit 1
fi
echo "Setting up ephemeral container..."
OVERLAY_DIR=`mktemp -d /tmp/lxc-lp-XXXXXXX`
sudo mount -t tmpfs none $OVERLAY_DIR
LXC_DIR=`sudo mktemp -d --tmpdir=/var/lib/lxc $LXC_BASE-temp-aufs-XXXXXXX`
LXC_NAME=`basename $LXC_DIR`
sudo mount -t $uniontype -o
br=$OVERLAY_DIR=rw:/var/lib/lxc/$LXC_BASE=ro,noplink none $LXC_DIR
if [ -n "$LXC_BIND" ]; then
sudo mkdir -p $LXC_DIR/rootfs$LXC_BIND
sudo mount --bind $LXC_BIND $LXC_DIR/rootfs$LXC_BIND
fi
sudo sed -i -e "s/$LXC_BASE/$LXC_NAME/" $LXC_DIR/fstab $LXC_DIR/config
$LXC_DIR/rootfs/etc/hostname $LXC_DIR/rootfs/etc/hosts
LEASES=$LXC_DIR/rootfs/var/lib/dhcp3/dhclient.eth0.leases
if [ ! -f $LEASES ]; then
LEASES=$LXC_DIR/rootfs/var/lib/dhcp/dhclient.leases
fi
sudo truncate -c -s0 $LEASES
echo "Starting up the container..."
sudo lxc-start -n $LXC_NAME -d
echo "$LXC_NAME is running"
echo "You connect with the command:"
echo " lxc-console -n $LXC_NAME"
lxc-monitor -Q -n $LXC_NAME
echo "Stopping lxc" >&2
sudo lxc-stop -n $LXC_NAME
sleep 2
if [ -n "$LXC_BIND" ]; then
echo "umounting bind" >&2
sudo umount $LXC_DIR/rootfs$LXC_BIND
fi
# echo "umounting lxc_dir $LXC_DIR" >&2
sudo umount $LXC_DIR
# echo "umounting overlay" >&2
sudo umount $OVERLAY_DIR
# echo "rming lxc_dir $LXC_DIR" >&2
sudo rmdir $LXC_DIR
# echo "rming overlay dir $OVERLAY_DIR" >&2
rmdir $OVERLAY_DIR
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