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doc/topics/highavailability/index.rst

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+.. _highavailability:
+
+==================================
+High Availability Features in Salt
+==================================
+
+Salt supports several features for high availability and fault tolerance.
+Brief documentation for these features is listed alongside their configuration
+parameters in :ref:`Configuration file examples <configuration/examples>`.
+
+Multimaster
+===========
+
+Salt minions can connect to multiple masters at one time by configuring the
+`master` configuration paramter as a YAML list of all the available masters.  By
+default, all masters are "hot", meaning that any master can direct commands to
+the Salt infrastructure.
+
+In a multimaster configuration, each master must have the same cryptographic
+keys, and minion keys must be accepted on all masters separately.  The contents
+of file_roots and pillar_roots need to be kept in sync with processes external
+to Salt as well
+
+A tutorial on setting up multimaster with "hot" masters is here:
+
+:doc:`Multimaster Tutorial </topics/tutorials/multimaster>`
+
+Multimaster with Failover
+=========================
+
+Changing the ``master_type`` parameter from ``standard`` to ``failover`` will
+cause minions to connect to the first responding master in the list of masters.
+Every ``master_alive_check`` seconds the minions will check to make sure
+the current master is still responding.  If the master does not respond,
+the minion will attempt to connect to the next master in the list.  If the
+minion runs out of masters, the list will be recycled in case dead masters
+have been restored.  Note that ``master_alive_check`` must be present in the
+minion configuration, or else the recurring job to check master status
+will not get scheduled.
+
+Failover can be combined with PKI-style encrypted keys, but PKI is NOT
+REQUIRED to use failover.
+
+Multimaster with PKI and Failover is discussed in 
+:doc:`this tutorial </topics/tutorials/multimaster_pki>`
+
+``master_type: failover`` can be combined with ``shuffle_masters: True``
+to spread minion connections across all masters (one master per
+minion, not each minion connecting to all masters).  Adding Salt Syndics
+into the mix makes it possible to create a load-balanced Salt infrastructure.
+If a master fails, minions will notice and select another master from the
+available list.
+
+Syndic
+======
+
+Salt's Syndic feature is a way to create differing infrastructure
+topologies.  It is not strictly an HA feature, but can be treated as such.
+
+With the syndic, a Salt infrastructure can be partitioned in such a way that
+certain masters control certain segments of the infrastructure, and "Master
+of Masters" nodes can control multiple segments underneath them.
+
+Syndics are covered in depth in :doc:`Salt Syndic </topics/topology/syndic>`.
+