Two years after it first offered open source code for Solaris, Sun Wednesday said it would open source the cluster technology for the operating system.

Sun will post the code to High Availability Clusters community on OpenSolaris.org in three phases, the first being a set of 24 high availability agents.

The donation of the code, called Open High Availability (HA) Cluster, is aimed at supporting application services that demand always-on availability and failover services. The agents allow users to add scalability or failover services to their cluster-enabled applications.

The Open HA Cluster agents are supported on the open source Solaris Express Developer Edition and Cluster Express, which Sun will make available in binary form in mid-July, according to company officials.

“At that point you can run an entirely open source environment based on Open Solaris and Cluster Express,” says Paul Steeves, director of Solaris marketing. Steeves said the agents also will be supported on Solaris Cluster 3.2 and on Solaris 10.

“All of this is just more commit from Sun to what we said two years ago, which was that we were going to open source everything,” Steeves said.

The Open HA Cluster code, which is being made available under the OpenSolaris Community Development and Distribution License (CDDL), will eventually provide an identical high-availability environment to that found in Sun’s proprietary Solaris Cluster 3.2.

Sun also is making available the source code for the Solaris Cluster Automated Test Environment (SCATE) to test new agents. The test framework and first test suite will be available this week. The agents include Solaris Containers, BEA Weblogic and PostgresSQL.

Sun’s release of the HA agents Wednesday marks the beginning of an 18-month process that will see 2 million lines of cluster code and 1 million lines of test code released via OpenSolaris.org.

The second phase, focusing on disaster recovery and storage replication, will come in December, according to Sun officials, and will include the Solaris Cluster Geographic Edition, which manages the availability of application services and data across geographically dispersed clusters.

In December 2008, Sun plans the third phase, which is the release of the code for the core Solaris Cluster infrastructure. That release will include failover and heart beat mechanisms, and the SCATE infrastructure tests and documentation.