Active-passive configuration for Sun Cluster 3.0

Adaptive Server for Sun Cluster 3.0 offers either an active-passive or an active-active setup.

An active-active setup includes two Adaptive Servers installed on two nodes of the cluster that are configured as companion servers. When the primary companion fails, the secondary companion takes over its workload. The active-active setup for Sun Cluster 3.0 is described in Chapter 11 of Using Sybase Failover in a High Availability System.

If Adaptive Server, or the node on which it is running, fails, the server and all its devices fails over to a secondary node. At the time of failover, all existing client connections are lost. Clients must reestablish their connections and resubmit their uncommitted transactions as soon as Adaptive Server is running on the secondary node. The failover of client connections (that is, reestablishing their connections after failover) can be done automatically by using the self-referencing hafailover entry in the interfaces file and setting the CS_HAFAILOVER connection property.

If your site includes more than two nodes in an active-passive setup, the server running on the primary node can fail over to any of the secondary nodes, as long as it can successfully host Adaptive Server and all its associated resources. The node list determines the order in which Adaptive Server fails over to the other nodes in the cluster.

Table 3-1 discusses the differences between an active-active setup and an active-passive setup.

**Table 3-1: Differences between active-active and active-passive**
Active-active	Active-passive
Setup: Two Adaptive Servers are configured as companion servers, each with an independent resource group. These companions run on the primary and secondary nodes, respectively, as individual servers until failover.	Setup: One Adaptive Server, running either on the primary node or on the secondary node. Only one Adaptive Server resource group exists, which is hosted by the primary node before failover and the secondary node after failover.
Failover: When failover occurs, the secondary companion takes over the devices, client connections, and so on from the primary companion. The secondary companion services the failed-over clients, as well as any new clients, until the primary companion fails back and resumes its activities.	Failover: When failover occurs, the Adaptive Server along with its associated resources and resource group is relocated to, and restarted on, the secondary node.
Failback: Failback is a planned event during which the primary companion takes back its devices and client connections from the secondary companion to resume its services.	Failback: Failback is a planned failover or relocation of the Adaptive Server resource group to the another node. Failback is not required, but can be used for administration.
Client Connection failover: During failover, clients connect to the secondary companion to resubmit their transactions. During failback clients connect to the primary companion to resubmit their transactions. Clients with the failover property reestablish their connections automatically	Client Connection failover: During failover and failback, clients connect to the same Adaptive Server to resubmit uncommitted transactions. Clients with the failover property reestablish their connections automatically.