diff --git a/source/core/replica-set-high-availability.txt b/source/core/replica-set-high-availability.txt index bf08d755802..05fd2b5bcea 100644 --- a/source/core/replica-set-high-availability.txt +++ b/source/core/replica-set-high-availability.txt @@ -9,36 +9,38 @@ Replica Set High Availability .. default-domain:: mongodb -Replica sets provide automatic failover to support autonomous -operation. If the :ref:`primary ` of a -replica set either steps down, becomes inaccessible, or becomes -otherwise ineligible to act as the primary, the replica set will -automatically hold an :doc:`election ` to -:doc:`elect ` one of the secondaries to -become primary. In some situations, the failover process may also -involve :doc:`rollbacks `. - -In most cases, failover occurs without administrator intervention. -However, if your MongoDB deployment does not failover accordingly, -consider both ability of the remaining members to form a majority as -well as the member eligibility to become primary. For instance, -network partitions can render some members inaccessible, and the -remaining members are unable to form a majority. Design your deployment -to ensure that a majority of set members can elect a primary in the -same facility as the core application systems. Additionally, to be -eligible to become primary, members must have a +:term:`Replica sets ` provide high availability through +automatic :term:`failover`. Automatic failover allows a +:term:`secondary` member of the replica set to become the +new :term:`primary` should the primary become inaccessible. + +Within a replica set, members hold the same information but are +otherwise autonomous. If the primary becomes inaccessible for any +reason, the replica set automatically holds an :doc:`election +` for a new primary. In some situations, +the failover process may also involve :doc:`rollbacks +`. + +You must configure your replica set correctly for failover to work. +Locate a majority of the replica set's voting members in one data +center. The center should hold all the members that are eligible to +become primary. Choose the facility that contains your core application +systems. Without these design patterns, network partitions might render +some members inaccessible, and the remaining members will not be able to +form a majority. + +To be eligible to become primary, a member must have a :data:`~local.system.replset.settings.members[n].priority` setting -greater than ``0``, have a state that is less than ten seconds behind -the last operation to the :term:`replica set`, and generally be *more* -up-to-date than the voting members. +greater than ``0`` and have a state that is fewer than ten seconds +behind the last operation to the replica set. Also, the member usually +must be *more* up-to-date than the voting members. Failover Processes ------------------ -To recover from the loss or inaccessiblity of the current primary, the -replica set failover processes involve an :doc:`election -` to elect a new primary, and, in certain -situations, :doc:`rollbacks `. +To recover from the loss or inaccessibility of the current primary, the +replica set holds an election. In rare situations, the replica set also +"rolls back" write operations. .. include:: /includes/dfn-list-replica-set-high-availability.rst