.. _modular-deployment-topology:

Modular Cluster Deployment
---------------------------------

.. _21.1|VOSS-837:


.. important::

   Choose between a unified node cluster deployment or a modular cluster deployment.

VOSS Automate is deployed as a modular cluster of multiple nodes
with High Availability (HA) and Disaster Recovery (DR) qualities.   

Each node can be assigned one or more of the following functional roles:

* WebProxy - load balances incoming HTTP requests across nodes.
* Application role node, clustered with other nodes to provide HA and DR capabilities
* Database role node, clustered with other nodes to provide HA and DR capabilities

The nginx web server is installed on the WebProxy and application role node,
but is configured differently for each role.

.. note::

   Also refer to the following topics:
   
   
   .. raw:: html
   
      <p>*&nbsp;&nbsp;<a href="../concepts-deployment-models-modular-recc-geo-redund.html">Multinode Modular Cluster with Application and Database Nodes</a></p>
   
   .. raw:: latex
   
      Multinode Modular Cluster with Application and Database Nodes in the Install Guide.
   
   .. raw:: html
   
      <p>*&nbsp;&nbsp;<a href="../install/concepts-modular-deployment-topology.html">Modular Cluster Deployment</a></p>
   
   .. raw:: latex
   
      Modular Cluster Deployment in the Install Guide.
   
   .. raw:: html
   
      <p>*&nbsp;&nbsp;<a href="../install/modular-multinode-installation.html">Modular Architecture Multinode Installation</a></p>
   
   .. raw:: latex
   
      Modular Architecture Multinode Installation in the Install Guide.
   
   .. raw:: html
   
      <p>*&nbsp;&nbsp;<a href="../platform/tasks-deployment-migrate-to-modular.html">Migrate a Unified Node Cluster to a Modular Cluster</a></p>
   
   .. raw:: latex
   
      Migrate a Unified Node Cluster to a Modular Cluster in the Platform Guide.

A load balancing function is required to offer HA (High Availability providing failover between redundant roles).

VOSS Automate supports deployment of either the WebProxy node or a DNS load balancer. Here are some
considerations in choosing a WebProxy node vs. DNS:

* The Proxy takes load off the application role node to deliver static content (HTML/JAVA scripts).
  When using DNS or a third-party load balancer, the application role node has to process this information.
* DNS does not know the state of the application role node.
* The WebProxy detects if an application role node is down or corrupt.
  In this case, the WebProxy will select the next application role node in a round robin scheme.

We recommend that you run no more than one application role node and one database role node and one WebProxy node on a physical server
(VMware server). When selecting disk infrastructure, high volume data access by database role replica sets must be considered
where different disk subsystems may be required depending on the performance of the disk infrastructure.

The following modular cluster topology is recommended (minimum):

.. important::

   Single node cluster topologies are not available for modular cluster
   deployments.

* Production with nodes: in a clustered system of 2 data centers:

  * DC1 = primary data center containing primary database node (highest database weight)
  * DC2 = data recovery data center
    
  The system comprises of the following nodes:

  * 3 nodes with application roles (2 in DC1; 1 in DC2)
  * 3 nodes with database roles (2 in DC1; 1 in DC2)
  * Maximum 2 WebProxy nodes if 2 data centers; offering load balancing.  The WebProxy nodes can be omitted if an external load balancer is available.