A field guide to Zones in OpenSolaris 2008.05

I have had a busy couple of months. After wrapping up work on Solaris 8 Containers (my teammate Steve ran the Solaris 9 Containers effort), I turned my attention to helping the Image Packaging team (rogue's gallery) with their efforts to get OpenSolaris 2008.05 out the door.

Among other things, I have been working hard to provide a basic level of zones functionality for OpenSolaris 2008.05. I wish I could have gotten more done, but today I want to cover what does and does not work. I want to be clear that Zones support in OpenSolaris 2008.05 and beyond will evolve substantially. To start, here's an example of configuring a zone on 2008.05:

# zonecfg -z donutshop
donutshop: No such zone configured
Use 'create' to begin configuring a new zone.
zonecfg:donutshop> create
zonecfg:donutshop> set zonepath=/zones/donutshop
zonecfg:donutshop> add net
zonecfg:donutshop:net> set physical=e1000g0
zonecfg:donutshop:net> set address=
zonecfg:donutshop:net> end
zonecfg:donutshop> add capped-cpu
zonecfg:donutshop:capped-cpu> set ncpus=1.5
zonecfg:donutshop:capped-cpu> end
zonecfg:donutshop> commit
zonecfg:donutshop> exit

# zoneadm list -vc
  ID NAME             STATUS     PATH                           BRAND    IP    
   0 global           running    /                              native   shared
   - donutshop        configured /zones/donutshop               ipkg     shared

If you're familiar with deploying zones, you can see that there is a lot which is familiar here.  But you can also see that donutshop isn't, as you would normally expect, using the native brand. Here we're using the ipkg brand. The reason is that commands like zoneadm and zonecfg have some special behaviors for native zones which presume that you're using a SystemV Packaging based OS. In the future, we'll make native less magical, and the zones you install will be branded native as you would expect. Jerry is actually working on that right now. Note also that I used the relatively new CPU Caps resource management feature to put some resource limits on the zone-- it's easy to do!. Now let's install the zone:

# zoneadm -z donutshop install
A ZFS file system has been created for this zone.

      Image: Preparing at /zones/donutshop/root ... done.
    Catalog: Retrieving from http://pkg.opensolaris.org:80/ ... done.
 Installing: (output follows)
DOWNLOAD                                    PKGS       FILES     XFER (MB)
Completed                                  49/49   7634/7634 206.85/206.85 

PHASE                                        ACTIONS
Install Phase                            12602/12602 

       Note: Man pages can be obtained by installing SUNWman
Postinstall: Copying SMF seed repository ... done.
Postinstall: Working around http://defect.opensolaris.org/bz/show_bug.cgi?id=681
Postinstall: Working around http://defect.opensolaris.org/bz/show_bug.cgi?id=741
       Done: Installation completed in 208.535 seconds.

 Next Steps: Boot the zone, then log into the zone console
             (zlogin -C) to complete the configuration process

There are a couple of things to notice, both in the configuration and in the install:
Non-global zones are not sparse, for now
Zones are said to be sparse if /usr, /lib, /platform, /sbin and optionally /opt are looped back, read-only, from the global zone. This allows a substantial disk space savings in the traditional zones model (which is that the zones have the same software installed as the global zone).

Whether we will ultimately choose to implement sparse zones, or not, is an open question. I plan to bring this question to the Zones community, and to some key customers, in the near future.

Zones are installed from a network repository
Unlike with traditional zones, which are sourced by copying bits from the global zone, here we simply spool the contents from the network repository. The upside is that this was easy to implement; the downside is that you must be connected to the network to deploy a zone. Getting the bits from the global zone is still desirable, but we don't have that implemented yet.

By default, zones are installed using the system's preferred authority (use pkg authority to see what that is set to). The preferred authority is the propagated into the zone. If you want to override that, you can specify a different repository using the new -a argument to zoneadm install:

# zoneadm -z donutshop install -a ipkg=http://ipkg.eng:80
Non-global zones are small
Traditionally, zones are installed with all of the same software that the global zone contains. In the case of "whole root" zones (the opposite of sparse), this means that non-global zones are about the same size as global zones-- easily at least a gigabyte in size.

Since we're not supporting sparse zones, I decided to pare down the install as much as I could, within reason: the default zone installation is just 206MB, and has a decent set of basic tools. But you have to add other stuff you might need. And we can even do more: some package refactoring should yield another 30-40MB of savings, as packagings like Tcl and Tk should not be needed by default. For example, Tk (5MB) gets dragged in as a dependency of python (the packaging system is written in python); Tcl (another 5MB) is dragged in by Tk. Tk then pulls in parts of X11. Smallness yields speed: when connected to a fast package repository server, I can install a zone in just 24 seconds!.

I'm really curious to know what reaction people will have to such minimalist environments. What do you think?

Once you start thinking about such small environments, some new concerns surface: vim (which in 2008.05 we're using as our vi implementation) is 17MB, or almost 9% of the disk space used by the zone!

Non-global zones are independent of the global zone
Because ipkg zones are branded, they exist independently of the global zone. This means that if you do an image-update of the global zone, you'll also need to update each of your zones, and ensure that they are kept in sync. For now this is a manual process-- in the future we'll make it less so.
ZFS support notes
OpenSolaris 2008.05 makes extensive use of ZFS, and enforces ZFS as the root filesystem. Additional filesystems are created for /export, /export/home and /opt. Non-global zones don't yet follow this convention. Additionally, I have sometimes seen our auto-zfs file system creation fail to work (you can see it working properly in the example above). We haven't yet tracked down that problem-- my suspicion is that there is a bad interaction with the 2008.05 filesystem layout's use of ZFS legacy mounts.

As a result of this (and for other reasons too, probably), zones don't participate in the boot-environment subsystem. This means that you won't get an automatic snapshot when you image-update your zone or install packages. That means no automatic rollback for zones. Again, this is something we will endeavor to fix.

Beware of bug 6684810
You may see a message like the following when you boot your zone:
zoneadm: zone 'donutshop': Unable to set route for interface lo0 to éÞùÞ$
zoneadm: zone 'donutshop': 
This is a known bug (6684810); fortunately the message is harmless.

In the next month, I hope to: take a vacation, launch a discussion with our community about sparse root zones, and to make a solid plan for the overall support of zones on OpenSolaris. I've got a lot to do, but that's easily balanced by the fact that I've been having a blast working on this project...


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