Sun Microsystems is to begin donating its Solaris clustering code to the open-source community, the latest move in the company's ongoing strategy to eventually make all of its software freely available.

It has been more than two years since Sun released OpenSolaris, an open-source version of its Solaris 10 Unix operating system. Since June 2005, the vendor has made other pieces of its software freely available, notably its core Java platform starting in November of last year.

Sun hopes opening up its software will enable its products to enter new markets and lead to more customers for its servers, storage and paid support services.

Known as Open High Availability Cluster, Sun will release its Solaris Cluster source code over the next 18 months through the High Availability (HA) Clusters community on the OpenSolaris Web site. Developers can use the code to help them build clustered and high-availability applications and services.

Sun will make the clustering source code available under its own open-source license, CDDL (Common Development and Distribution License), said Paul Steeves, director of Solaris marketing at Sun. There are no plans to also provide the code under the GNU general public license (GPL) as Sun did with Java

That situation might change, if, as rumoured, Sun decides to also provide OpenSolaris under GPLv3. The third version of the GPL is due to be finalised later this week. OpenSolaris is currently offered under CDDL.

Sun will make three major contributions to the clustering code, according to Steeves.

The first donation, due out this week, is focused on application modules or agents that allow open-source or commercial applications to become highly available in a clustered environment. Sun will make the code available for 24 of the high-availability agents it offers with its commercially available Solaris Cluster software.

Among the agents are modules for Sun's Solaris Containers virtualisation technology, BEA Systems's WebLogic application server and the open-source PostgreSQL database.

"There are a couple of agents we need to work through, that have encumbrances," Steeves said, where Sun doesn't hold enough rights to release the code under CDDL. These modules include agents for Oracle's Real Application Clusters (RAC) technology, Sybase's database and IBM's WebSphere middleware. "We intend to release them once we've worked through the licensing," he added.

Sun will also provide documentation for the agents along with the source code for the Solaris Cluster Automated Test Environment (SCATE) so that developers can test new agents they develop, Steeves said.

Agents written using Open HA Cluster will run on Cluster Express, a binary version of Solaris Cluster, which Sun plans to release in a few weeks, Steeves said. The agents will also run on the latest version of Sun's commercial clustering product, Solaris Cluster 3.2, which debuted in January, and runs on the Solaris 9 and 10 operating systems.

The second donation will likely appear in December, Steeves said, and will include code for the Solaris Cluster Geographic Edition, software that enables multisite disaster recovery.

At the end of the 18-month period, Sun will release the code for the core Solaris Cluster infrastructure along with more documentation and additional SCATE infrastructure tests.

In total, Sun will make around 2 million lines of clustering source code available, Steeves said. By comparison, Sun's donation of Java Platform Standard Edition (Java SE) software to the open-source community represents over 6 million lines of code.