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<refsect1 id='failover'>
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<title>FAILOVER</title>
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The failover feature allows back ends to automatically switch to a different
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server if the primary server fails.
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<refsect2 id='failover_syntax'>
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<title>Failover Syntax</title>
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The list of servers is given as a comma-separated list; any number of spaces
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is allowed around the comma. The servers are listed in order of
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preference. The list can contain any number of servers.
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<refsect2 id='failover_mechanism'>
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<title>The Failover Mechanism</title>
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The failover mechanism distinguishes between a machine and a service. The
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back end first tries to resolve the hostname of a given machine; if this
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resolution attempt fails, the machine is considered offline. No further
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attempts are made to connect to this machine for any other service. If the
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resolution attempt succeeds, the back end tries to connect to a service on
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this machine. If the service connection attempt fails, then only this
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particular service is considered offline and the back end automatically
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switches over to the next service. The machine is still considered online
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and might still be tried for another service.
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Further connection attempts are made to machines or services marked as
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offline after a specified period of time; this is currently hard coded to 30
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If there are no more machines to try, the back end as a whole switches to
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offline mode, and then attempts to reconnect every 30 seconds.