Solaris Live Upgrade, ZFS and Zones

I've been working on this problem for a few days and have only just solved it, so thought it might be worth sharing...

Solaris is a very powerful operating system with some great features. Zones brought Docker-like containers to Solaris back in 2005, ZFS is one of the most advanced filesystems currently available, and the Live Upgrade capability is highly underrated and is a great way to patch a server while ensure you have a back out plan.

All good stuff, but when you put Live Upgrade into a mix of Zones and ZFS, things get a bit flakey.

The issue I was having was that when I ran the "lupc -S" (Live Upgrade Preflight Check) script on my zone, I'd get the following message:

# lupc -S
This system has Patch level/IDR  of 121430-92.
Please check MOS (My Oracle Support) to verify that the latest Live Upgrade patch is installed -- lupc does not verify patch versions.

Zonepath of zone is the mountpoint of top level dataset.
This configuration is unsupported

Oracle has a document on My Oracle Support: "List of currently unsupported Live Upgrade (LU) configurations (Doc ID 1396382.1)" which lists a lot of ways in which Live Upgrade won't work(!). On checking this document for the top level dataset issue, it gives the following text:

If ZFS root pool resides on one pool (say rpool) with zone residing on toplevel dataset of a different pool (say newpool) mounted on /newpool i.e. zonepath=/newpool, the lucreate would fail.

Okay, except that's not what I've got. My zone, s1, has a zonepath set to  /zones/s1. The zpool is called "zones" and "s1" is a separate ZFS filesystem in this dataset.

What the system is actually complaining about is that the zpool is called "zones" and is mounted as "/zones". The workaround is to set the ZFS mountpoint to be something different from the pool name.

For example,  I created a new ZFS filesystem under zones called "zoneroot":

# zfs create zones/zoneroot

Then (and this is the important bit), I set the mountpoint to something else:

# zfs set mountpoint=/zoneroot zones/zoneroot

Running zfs list for this dataset shows:

zones/zoneroot                  1.80G   122G    32K  /zoneroot

Now, I can create a zone, let's call it "s2":

# zonecfg -z s2
s2: No such zone configured
Use 'create' to begin configuring a new zone.
zonecfg:s2> create
zonecfg:s2> set zonepath=/zoneroot/s2
zonecfg:s2> verify
zonecfg:s2> commit
zonecfg:s2> exit

On installing this zone, a new ZFS file system is created, /zoneroot/s2.

Now, when running the "lupc -S" command, Live Upgrade doesn't complain about unconfigured configurations!