Amer Networks E5Web GUI - Manual (Page 699)

Chapter 11: High Availability
This chapter describes the high availability fault-tolerance feature in Clavister Security Gateways.
• Overview, page 699
• HA Mechanisms, page 702
• Setting Up HA, page 705
• HA Issues, page 712
• Upgrading an HA Cluster, page 715
• Link Monitoring and HA, page 717
• HA Advanced Settings, page 718
11.1. Overview
HA Clusters
cOS Core High Availability (HA) provides a fault tolerant capability to Clavister Security Gateway
installations. HA works by adding a back-up slave Clavister Security Gateway to an existing
master security gateway. The master and slave are connected together and make up a logical HA
Cluster. One of the units in a cluster will be active when the other unit is inactive and on standby.
Initially, the cluster slave will be inactive and will only monitor the activity of the master. If the
slave detects that the master has become inoperative, an HA failover takes place and the slave
becomes active, assuming processing responsibility for all traffic. If the master later becomes
operative again, the slave will continue to be active but the master will now monitor the slave
with failover only taking place if the slave fails. This is sometimes known as an active-passive
implementation of fault tolerance.
The Master and Active Units
When reading this section on HA, it should be kept in mind that the master unit in a cluster is not
always the same as the active unit in a cluster.
The active unit is the Clavister Security Gateway that is actually processing all traffic at a given
point in time. This could be the slave unit if a failover has occurred because the master is no
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