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This page describes a High Availability environment, how High Availability components recover in the event of such a failure, and what actions, if any, the user must take.
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- Two Universal Controller instances (cluster nodes)
- Two Universal Message Service (OMS) network communications providers in an OMS cluster
- Four Universal Agent (Agent) machines
The components in blue are active and operating. The components in gray are available for operations but currently are inactive (passive).
See 64323649 High Availability Components for a detailed description of how each component type functions in a High Availability environment.
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In a High Availability environment, passive cluster nodes play the role of standby servers to the active (primary) cluster nodes server. All running cluster nodes issue heartbeats and check the mode (status) of other running cluster nodes, both when they start up and continuously during operations. If a cluster node that currently is processing work can no longer do so, one of the other cluster nodes will take over and continue processing.
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A Universal Controller HA configuration can use a single OMS server, that is not an HA cluster, with the understanding that a single OMS server would introduce a single point of failure. Using an OMS HA cluster is recommended.
See 64323649 High Availability Configuration for information on how these connections are made.
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Cluster nodes in Passive mode can perform limited system processing functions. |
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A cluster node starts in 64323649 Passive mode. It then determines if it should remain in Passive mode or switch to 64323649 Active mode.
The following flow chart describes how a cluster node determines its mode at start-up:
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When all cluster nodes have started, each one continuously monitors the heartbeats of the other running cluster nodes.
If a 64323649 Passive cluster node determines that the 64323649 Active cluster node is no longer running, the Passive cluster node automatically takes over as the Active cluster node based upon the same criteria described above.
This determination is made as follows:
Step 1 | The Active cluster node sends a heartbeat by updating a timestamp in the database. The heartbeat interval is 10 (seconds). |
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Step 2 | All Passive cluster nodes check the Active cluster node's timestamp to determine if it is current. (This check runs every 60 seconds.) |
Step 3 | If a Passive cluster node determines that the Active cluster node's timestamp is stale, failover occurs: the Passive cluster node changes the mode of the Active cluster node to 64323649 Offline and takes over as the Active cluster node. If more than one cluster node is operating in Passive mode, the first cluster node eligible to become Active that determines that the Active cluster node is not running becomes the Active cluster node. A stale cluster node is one whose timestamp is older than 5 minutes. |
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Step 1 | Access the new Active cluster node in your browser. To determine which cluster node is now Active, check the Mode column on the Cluster Nodes list in the user interface (see 64323649 Viewing Cluster Node Status, below). |
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Step 2 | If you were adding, deleting, or updating records at the time of the failure, check the record you were working on. Any data you had not yet saved will be lost. |
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