Progress
Database Administration
Guide and Reference
Failover Manager
The Failover Manager is an image running on each node in the cluster. It handles the reading of the Failover Group information and performs the startup and shut down of the Failover Objects in the specific order in which they were defined.
The Failover Manager determines when one node has either crashed or has shutdown in some manner, then it performs actions based on the objects that were running on the failed node. The Failover Manager also allows for manual intervention to failover specific Failover Groups as if the primary node failed.
Failover Groups
Failover Groups are created by the cluster system manager using the Cluster Administrator interface. The Failover Group must contain at least one Failover Object and a cluster node must be chosen as the primary node. Within each Failover Group, the Cluster Administrator requires that there be at least one shared disk Failover Object.
After these minimum requirements are met, any number of other Failover Objects can be placed into or removed from the Failover Group. When removing Failover Objects from a Failover Group the Cluster Administrator will ensure that there is at least one object in the group.
Failover Groups can be deleted, in which case the Failover Objects that were in the group are returned to the general pool of Failover Objects. A Failover Group contains all the dependencies to allow the group to function as a unit on a node.
Failover Objects
Failover Objects are defined by the cluster manager using the Cluster Administrator interface. Failover Objects are created and placed into a pool of available objects. When the Failover Group is created, an object is placed into the group and removed from the pool of objects.
A Failover Object cannot be placed into two Failover Groups; in this scenario, two identical objects would need to be created. Failover Objects have Startup and Shutdown attributes. When a Failover Group is brought online the startup option is run; conversely, when the Failover Manager determines that the group must be failed over, the shutdown option is run.
The two primary Failover Objects are Shared Disks and TCP/IP Alias. These objects give the cluster the ability to make the cluster nodes transparent to the clients.
The shared disk objects are created automatically when the shared disks are given a name by the Cluster Administrator interface. When a disk object is placed into a Failover Group, it is brought online to the primary node by the Failover Manager. Due to the nature of SCSI, only one node can directly access or own a shared disk at any one time.
The TCP/IP alias objects are defined by the cluster manager using IP addresses that are not currently assigned to any other node. The cluster TCP/IP alias allows clients to access the nodes in the cluster without the clients needing to know to which nodes they are connected.
A TCP/IP alias object is associated with only one node at a time and migrates from the primary to the secondary node, when the Failover Manager fails over a Failover Group. In this scenario, the client just reconnects to the same name, but now the client is attached to a different node.
There can be more than one TCP/IP alias name per cluster. This happens when each node is acting as a server to a different database and defines only one IP address with the database server. Management of the TCP/IP alias name dependencies is left up to the cluster system manager. It is recommended that a TCP/IP alias object be present for each Failover Group that has objects requiring TCP/IP services.
For Progress, the only other Failover Object used is the script object. This object allows the Failover Manager to run either a script or a specific image as defined by the cluster system manager.
Scripts or images that are to be run can be placed either onto a shared storage device or onto the system disk of each node. When using the system disk, the drive letter for the system disk must be the same on both nodes or an environment variable must be used on both nodes to mask the drive letter.
When using shared storage for a script object script or image, the shared disk object must be placed before the script object in the order of the Failover Group. This ensures the disk is online before the Failover Manager attempts to run the script object.
Progress Example
For Progress, a Failover Group might be comprised of a shared disk object, a TCP/IP alias object, and a script object that would start a database server. The database server must first have a disk and then a TCP/IP address before the server can start. The script object can either start the database server directly or run a written script that starts the database server.
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