Solaris Containers (including Solaris Zones) is a an implementation of operating system-level virtualization technology first made available as part of Solaris 10. A Solaris Container is the combination of system resource controls and the boundary separation provided by zones. Zones act as completely isolated virtual servers within a single operating system instance. By consolidating multiple sets of application services onto one system by placing each into isolated virtual server containers, system administrators can reduce cost and provide all the same protections of separate machines on a single machine.
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Terminology
There is always one zone defined, named the "global" zone. Zones hosted by a global zone are known as "non-global zones" but are sometimes just called "zones." The term "local zone" is specifically discouraged, since in this usage "local" is not an antonym of "global." The global zone encompasses all processes running on the system, whether or not these processes are running within a non-global zone. Unless otherwise noted, "zone" will refer to non-global zones in this article.
Description
Each zone has its own node name, virtual network interfaces, and storage assigned to it; there is no requirement for a zone to have any minimum amount of dedicated hardware other than the disk storage necessary for its unique configuration. Specifically, it does not require a dedicated CPU, memory, physical network interface or HBA, although any of these can be allocated specifically to one zone. Each zone has a security boundary surrounding it which prevents a process associated with one zone from interacting with or observing processes in other zones. Each zone can be configured with its own separate user list. The system automatically manages user ID conflicts; that is, two zones on a system could have a user ID 10000 defined, and each would be mapped to its own unique global identifier. A zone can be assigned to a resource pool (processor set plus scheduling class) to guarantee certain usage, or can be given shares via fair-share scheduling. A zone can be in one of the following states:
- Configured: configuration was completed and committed
- Installed: the packages have been successfully installed
- Ready: the virtual platform has been established
- Running: the zone booted successfully and is now running
- Shutting down: the zone is in the process of shutting down - this is a temporary state, leading to "Down"
- Down: the zone has completed the shut down process and is down - this is a temporary state, leading to "Installed"
Some programs cannot be executed from within a non-global zone; typically this is because the application requires privileges that cannot be granted within a container. As a zone does not have its own separate kernel (in contrast to a hardware virtual machine), applications that require direct manipulation of kernel features, such as the ability to directly read or alter kernel memory space, may not work inside of a container.
Resources needed
Zones induce a very low overhead on CPU and memory. Currently a maximum of 8191 non-global zones can be created within a single operating system instance. "Sparse Zones", in which most filesystem content is shared with the global zone, can take as little as 50MB of disk space. "Whole Root Zones", in which each zone has its own copy of its operating system files, may occupy anywhere from several hundred megabytes to several gigabytes, depending on installed software. Even with Whole Root Zones, disk space requirements can be negligible if the zone's OS file system is a ZFS clone of the global zone image, since only the blocks different from a snapshot image need to be stored on disk; this method also makes it possible to create new zones in a few seconds.
Branded zones
Although all zones on the system share a common kernel, an additional feature set has been added called branded zones, or BrandZ for short, which allows individual zones to emulate an OS environment other than the native one of the global OS.[1] This non-native environment is dubbed a "brand", which plugs into the BrandZ framework. The brand for a zone is set at the time the zone is created, and is implemented with interposition points within the OS kernel that can be used to change the behavior of syscalls, process loading, thread creation, and other elements. Two brands that have been implemented are Solaris Containers for Linux Applications and Solaris 8 Containers. The former is available when Solaris is run on x86 systems, and provides an environment that emulates Red Hat Enterprise Linux 3. Libraries from Red Hat 3 or an equivalent distribution such as CentOS are required to complete the emulated environment. The latter brand allows an existing Solaris 8 environment to be copied and relocated in a Solaris 10 zone, and is the foundation of the Solaris 8 Migration Assistant offering from Sun.
Documentation
Several resources for Solaris Zones documentation exist. The Solaris operating system provides man pages by default but more detailed documentation must be found at various on-line technical resources. The first published document and hands-on reference for Solaris Zones was written in Feb 2004 by Dennis Clarke at Blastwave.org and this document still provides the essentials to getting started. This document was greatly expanded upon by Brendan Gregg in Jul 2005 and currently resides at SolarisInternals.com. More extensive documents may be found at the Sun Microsystems documentation site.
Current implementation issues
As of the Solaris 10 8/07 release, the following limitation in Solaris Containers still exists. This issue may be resolved in the future.
- A zone cannot export a local directory via the Solaris NFS server.[2] [3] NFS server software that is not implemented in the Solaris kernel may work.
Similar technologies
Other implementations of operating system-level virtualization technology include OpenVZ/Virtuozzo, Linux-VServer, FreeBSD Jails, FreeVPS and AIX Workload Partitions.
References
- ^ BrandZ/SCLA FAQ. OpenSolaris Project. Retrieved on 2007-10-19.
- ^ RFE: Zones should be able to be NFS servers. OpenSolaris BugTracker (2003-12-07). Retrieved on 2007-02-20.
- ^ NFS server in zones. zones-discuss (2007-02-14). Retrieved on 2007-02-20.
