Solaris Containers

OS level virtualisation

Solaris Containers (including Solaris Zones) is an implementation of operating system level virtualization technology for x86 and SPARC systems, first released publicly in February 2004 in build 51 beta of Solaris 10, and subsequently in the first full release of Solaris 10, 2005. It is present in illumos (formerly OpenSolaris) distributions, such as OpenIndiana, SmartOS, Tribblix and OmniOS, as well as in the official Oracle Solaris 11 release. 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 and by placing each into isolated virtual server containers, system administrators can reduce cost and provide most of the same protections of separate machines on a single machine.

The name of this technology changed during development and the pre launch public events. Before the launch of Solaris Zones in 2005, a Solaris Container was any type of workload constrained by Solaris resource management features. The latter had been a separate software package in earlier history. By 2007 the term Solaris Containers came to mean a Solaris Zone combined with resource management controls. Later, there was a gradual move such that Solaris Containers specifically referred to non global zones, with or without additional Resource Management. 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 has visibility of all resource on the system, whether these are associated with the global zone or a non global zone. Unless otherwise noted, "zone" will refer to non global zones in this article. To simplify terminology, Oracle dropped the use of the term Container in Solaris 11, and has reverted to use of the term Solaris Zone irrespective of the use of resource management controls.

Zones induce a very low overhead on CPU and memory. Most types of zones share the global zone's virtual address space. A zone can be assigned to a resource pool (processor set plus scheduling class) to guarantee certain usage, or can be capped at a fixed compute capacity ("capped CPU") or can be given shares via fair share scheduling. 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 50 MB 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. The 8191 limits arises from the limit of 8,192 loopback connections per Solaris instance. Each zone needs a loopback connection. The global zone gets one, leaving 8,191 for the non global zones. 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.

The Solaris operating system provides man pages for Solaris Containers by default; more detailed documentation can be found at various on line technical resources. The first published document and hands on reference for Solaris Zones was written in February 2004 by Dennis Clarke at Blastwave, providing the essentials to getting started. This document was greatly expanded upon by Brendan Gregg in July 2005. The Solaris 8 and Solaris 9 Containers were documented in detail by Dennis Clarke at Blastwave again in April 2008. The Blastwave Solaris 8 and Solaris 9 Containers document was very early in the release cycle of the Solaris Containers technology and the actions and implementation at Blastwave resulted in a followup by Sun Microsystems marketing. The book Oracle Solaris 10 System Virtualization Essentials written by Jeff Victor, et al., offers feature details and best practices. More extensive documentation may be found at the Oracle documentation site.

As of Solaris 10 10/08, Branded Zones are supported on the sun4us architecture (Fujitsu PRIMEPOWER servers) through packages FJSVs8brandr and FJSVs9brandr.