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26 Planning the installation
About simple failover
■ Once the IPS Service fails away from the first server in the ordered list, it
periodically checks if server #1 is back, based on the fail back interval.
See “About the fail back interval” on page 26.
■ When the fail back interval expires, the IPS Service checks if server #1 is
available. If server #1 is available, the IPS Service starts using it
immediately. If server #1 is not available, the IPS Service continues to use
the current alternate server; the IPS Service does not traverse the entire
ordered list of management servers.
Simple failover with static load balancing works as described in the following
example:
■ Suppose you have two Tomcat servers pointing to a single database, and
two agents.
■ You initially configure Agent1 with a management server list of Tomcat1,
Tomcat2. You initially configure Agent2 with a management server list of
Tomcat2, Tomcat1.
■ After installation completes, Agent1 should be talking to Tomcat1, and
Agent2 should be talking to Tomcat2.
■ Take Tomcat1 off the network.
■ Agent1 should fail talking to Tomcat1 and switch to Tomcat2. Now both
agents are talking to Tomcat2.
■ Put Tomcat1 back on the network.
■ Wait longer than the fail back interval.
■ Agent1 should fail back to Tomcat1. Agent2 continues to use Tomcat2.
Everything is back to the initial state; both agents should be communicating
successfully with their original Tomcat servers.
About the fail back interval
Once an agent fails away from the first server in an ordered list, the agent
periodically checks if the first server is back. The agent uses a fail back interval
to determine when to perform this server check. By default, the agent performs
the server check every 60 minutes.
For example, suppose you configured three management servers. The primary
server #1 and alternate server #2 have failed; alternate server #3 is working.
When the fail back interval expires, the agent checks if server #1 is available. If
server #1 is available, the agent immediately starts using server #1. If server #1
is not available, the agent continues to use server #3; it does not recheck the
ordered list of servers. The agent resets the fail back interval, so it can perform
future server checks.