[lxc-devel] [PATCH] lxc-clone: support 'permanent ephemeral' containers

[Stéphane Graber]

On 03/27/2013 10:01 AM, Serge Hallyn wrote:
> All of this needs a rewrite/redesign, and that will be coming (details
> below), but for now
> 
> You can start 'non-ephemeral ephemeral' containers using
> 
> 	lxc-start-ephemeral -o oldname -n newname --keep-data
> 
> When you shut that down, the container stick around and can be
> restarted.  Now lxc-clone will recognize such a container by the
> presence of the delta0/ which contains the read-write overlayfs
> layer.  This means you can do incremental development of containers,
> i.e.
> 
> 	lxc-create -t ubuntu -n r1
> 	lxc-start-ephemeral --keep-data -o r1 -n r1-2
> 	# make some changes, poweroff
> 	lxc-clone -o r1-2 -n r1-3
> 	# make some changes...
> 	lxc-clone -o r1-3 -n r1-4
> 	# etc...
> 
> Now, as for design changes...  from a higher level
> 
> 	1. lxc-clone should be re-written in c and exported through the
> 	   api.
> 	2. lxc-clone should support overlayfs and aufs
> 	3. lxc-start-ephemeral should become a thin layer which clones a
> 	   container, starts and stops and destroys it.
> 
> at a lower level,
> 
> 	1. the api should support container->setup_mounts
> 	2. lxc-clone should be written as a set of backend classes which
> 	   can copy mounts to each other.  So when you load a container
> 	   which is lvm-backed, it creates a lvm backend class.  That
> 	   class instance can be converted into a loopback or qemu-nbd
> 	   or directory backed class.  A directory-backed class can be
> 	   converted into a overlayfs or aufs backed class, which (a)
> 	   uses the dirctory-backed class as the read-only base, and (b)
> 	   pins the base container (so it can't be deleted until all
> 	   snapshots are deleted).
> 
> Signed-off-by: Serge Hallyn <serge.hallyn at ubuntu.com>

Looks good.

Acked-by: Stéphane Graber <stgraber at ubuntu.com>

And pushed to staging.

> ---
>  src/lxc/lxc-clone.in | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/src/lxc/lxc-clone.in b/src/lxc/lxc-clone.in
> index 291db30..4c8acb4 100755
> --- a/src/lxc/lxc-clone.in
> +++ b/src/lxc/lxc-clone.in
> @@ -251,6 +251,23 @@ elif which btrfs >/dev/null 2>&1 && btrfs subvolume list $oldroot >/dev/null 2>&
>      # if oldroot is a btrfs subvolume, assume they want a snapshot
>      btrfs subvolume snapshot "$oldroot" "$rootfs" 2>&1 || { echo "$(basename $0): btrfs snapshot failed" >&2; false; }
>      echo "lxc.rootfs = $rootfs" >> "$lxc_path/$lxc_new/config"
> +elif [ -d $lxc_path/$lxc_orig/delta0 ]; then # this is a quasi-ephemeral container
> +    if [ $container_running = "True" ]; then
> +        echo "$(basename $0): container $lxc_orig is running." >&2
> +        cleanup
> +    fi
> +    rsync -Hax $lxc_path/$lxc_orig/delta0 $lxc_path/$lxc_new/
> +    touch $lxc_path/$lxc_new/configured
> +    cp -f $lxc_path/$lxc_orig/pre-mount $lxc_path/$lxc_new/
> +    sed -i "s@$lxc_path/$lxc_orig@$lxc_path/$lxc_new at g" $lxc_path/$lxc_new/config
> +    sed -i "s@$lxc_path/$lxc_orig@$lxc_path/$lxc_new at g" $lxc_path/$lxc_new/pre-mount
> +    sed -i "s at LXC_NAME=\"$lxc_orig at LXC_NAME=\"$lxc_new@" $lxc_path/$lxc_new/pre-mount
> +    # lxc-start-ephemeral will have updated /etc/hostname and such under the
> +    # delta0, so just mounting the delta should suffice.
> +    mkdir -p $rootfs
> +    mount --bind $lxc_path/$lxc_new/delta0 $rootfs
> +    mounted=1
> +    echo "lxc.rootfs = $rootfs" >> "$lxc_path/$lxc_new/config"
>  else
>      if [ $snapshot = "yes" ]; then
>          echo "$(basename $0): cannot snapshot a directory" >&2
> 


-- 
Stéphane Graber
Ubuntu developer
http://www.ubuntu.com

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