.. _two_node_cluster_topology:

Two-node Cluster with Unified Nodes
-----------------------------------

.. _19.1.1|VOSS-475:

In order to achieve Geo-Redundancy using the Unified nodes, you need the consider
the following:

* Two unified nodes - each node combining application and database roles -
  are clustered and optionally split over two geographically disparate locations.
* (Optional) Two web proxy nodes can be used. It may be omitted if an external load balancer is available.
* Web proxy and unified nodes can be contained in separate firewalled networks.
* Database synchronization takes place from primary to secondary unified nodes, thereby offering Disaster Recovery 
  if the primary node fails.
* If the secondary unified node has *more than 10ms latency* with the primary unified node,
  it must be configured to be in the *same* geographical location.


.. important::
   With only two Unified nodes, with or without Web proxies, there is no High Availability.
   The database on the primary node is read/write, while the database on the secondary is read only.

   Only redundancy is available.

  * If the primary node fails, a manual delete of the primary
    node on the secondary and a cluster provision will be needed.
  * If the secondary node fails, it needs to be replaced.

  Refer to the topic on DR Failover and Recovery in a 2 Node Cluster in the
  Platform Guide.

 
The diagram below illustrates the two node cluster:


|2-node-cluster|


.. |2-node-cluster| image:: /src/images/2-node-cluster.png