A high availability cluster includes two or more machines that are configured so that, if one machine (or application) is brought down, the second machine assumes the workload of both machines. Each of these machines is called one node of the high availability cluster. A high availability cluster is typically used in an environment that must always be available, for example, a banking system to which clients must connect continuously, 365 days a year.
Sybase’s Failover product enables Adaptive Server to work in a high availability cluster in active-active or active-passive configuration.
An active-active setup is a two node configuration where both nodes in the cluster include Adaptive Servers managing independent workloads, and are capable of taking over each other’s workload in the event of a failure.
The Adaptive Server that takes over the workload is called a secondary companion, and the Adaptive Server that fails is called the primary companion. Together they are companion servers. This movement from one node to another is called failover. After the primary companion is ready to resume its workload, it is moved back to its original node. This movement is called failback.
During failover clients connected to the primary companion using the failover property automatically reestablish their network connections to the secondary companion.
You must tune your operating system to successfully manage both Adaptive Servers during failover. See your operating system documentation for information about reconfiguring your system for high availability.
An Adaptive Server configured for failover in an active-active setup
can be shut down using the shutdown command only
after you have suspended Adaptive Server from the companion configuration,
at both the server level and the platform level. For more information,
see the configuration chapter of this manual for your platform.
The active-passive configuration is a multi-node setup that involves a single Adaptive Server, a primary node on which the Adaptive Server primarily runs, and a set of secondary nodes which can potentially host the Adaptive Server and its resources.
When the Adaptive Server can no longer continue to run on the primary node, failover occurs and the Adaptive Server is relocated and restarted on a secondary node. The Adaptive Server can be moved back to the primary node after it recovers and when it can successfully host the Adaptive Server and any associated resources.
In the case of failover or failback, clients connected to the Adaptive Server re-establish their network connections and resubmit any uncommitted transactions when the Adaptive Server is restarted on the secondary node. Client connections using the failover property automatically reestablish their connections.
Sybase provides active-passive configuration support for Sun Cluster 3.0. Contact your provider for other cluster platforms. See Chapter 12, “Active-Passive Configuration for Sun Cluster 3.0,” for detailed information on configuring Adaptive Server in the active-passive mode for Sun Cluster 3.0. Other chapters of this manual pertain to the active-active configuration unless otherwise specified.
Adaptive Server configured for failover in an active-passive setup
can be shut down using the shutdown command only
after you disable monitoring on the Adaptive Server at the platform
level.
