High availability clusters can stretch across long distances, such as nodes across buildings, cities or even continents. The goal of HA clusters is to support enterprise business continuity by providing location-independent load balancing and failover.
In high availability (HA) mode, two SSB units (called master and slave nodes) with identical configuration are operating simultaneously. The master shares all data with the slave node, and if the master node stops functioning, the other one becomes immediately active, so the servers are continuously accessible.
You can find more information on managing a high availability SSB cluster in Managing a high availability SSB cluster.
The SSB firmware is separated into two parts: an external and an internal firmware.
The external firmware (also called boot firmware) boots up SSB, provides the high availability support, and starts the internal firmware. The external firmware changes very rarely.
The internal firmware (also called core firmware) handles everything else: provides the web interface, receives and processes log messages and so on. The internal firmware is updated regularly as new features are added to SSB.
Both parts of the firmware can be updated from the SSB web interface. For details, see Upgrading SSB.
When powering on the SSB nodes in high availability mode, both nodes boot and start the boot firmware. The boot firmware then determines which unit is the master: the core firmware is started only on the master node.
Upgrading the SSB firmware via the web interface automatically upgrades the firmware on both nodes.
As of June 2011, the following release policy applies to syslog-ng Store Box:
Long Term Supported or LTS releases (for example, SSB 3 LTS) are supported for 3 years after their original publication date and for 1 year after the next LTS release is published (whichever date is later). The second digit of the revisions of such releases is 0 (for example, SSB 3.0.1). Maintenance releases to LTS releases contain only bugfixes and security updates.
Feature releases (for example, SSB 3 F1) are supported for 6 months after their original publication date and for 2 months after the succeeding Feature or LTS Release is published (whichever date is later). Feature releases contain enhancements and new features, presumably 1-3 new feature per release. Only the last feature release is supported (for example, when a new feature release comes out, the last one becomes unsupported within two months).
For a full description on stable and feature releases, open the SSB product page on the Support Portal and navigate to Product Life Cycle & Policies > Product Support Policies > Software Product Support Lifecycle Policy.
Downgrading from a feature release is not supported. If you upgrade from an LTS release (for example, 3.0) to a feature release (3.1), you have to keep upgrading with each new feature release until the next LTS version (in this case, 4.0) is published.