Re: [atomic-devel] docker storage setup

[Colin Walters <walters verbum org>]

I can definitely see this evolving into some other language (if it was
Python, it could use python-blivet, if it was C, it's a lot easier to
talk to LVM directly).  Python would probably be OK given that it's a
one-shot service and not resident in memory.

One major thing; to put this together, we also need to edit
/etc/sysconfig/docker-storage.  

In the cloud case, the device name that an EBS volume will use is not
necessarily going to be predictable, and that seems like it'd make it
harder to use this.  Say an admin starts out with a micro instance to
toy with, but stores data persistently in an EBS volume they've run
"pvcreate" on.  Then they want to upgrade to m1.large, and attach the
existing volume to the new instance.
In this case, the unique predictable identifier would be the PV UUID,
right?

There are a lot of scenarios here, and we're not going to be able to
capture them all of course.  I think this will work well for "boot OS
and have storage expand on default disk" case which is definitely the
most important for initial experience.  Admins doing serious Docker in
production will need to be able to dive into the storage guide and LVM
directly.

BTW, I tested your script by stopping docker.service and deleting the
docker-data/docker-meta from an existing instance, and I had to change
this:

diff --git a/docker-storage-setup.sh b/docker-storage-setup.sh
index 64af49a..13d5a0b 100644
--- a/docker-storage-setup.sh
+++ b/docker-storage-setup.sh
@@ -139,7 +139,7 @@ fi
 # more difficult do to the range of possible inputs.
 VG_FREE_EXTS=$( vgs --noheadings --nosuffix --units s -o vg_free $VG )
 META_SIZE=$(( $VG_FREE_EXTS / 1000 + 1 ))
-lvcreate -l ${META_SIZE}S -n docker-meta $VG
+lvcreate -L ${META_SIZE}S -n docker-meta $VG
 if [ -n "$DATA_SIZE" ]; then
   # TODO: Error handling when DATA_SIZE > available space.
   lvcreate -L $DATA_SIZE -n docker-data $VG