anchor.diff:  <% current_page.data.title = "High Availability in " + vars.product_short if vars.product_name != 'CF'  %>
   
   
  -
   This topic describes the components used to ensure high availability in <%= vars.app_runtime_full %>, vertical and horizontal scaling, and the infrastructure required to support scaling component VMs for high availability.
   
   
  -## <a id='azs'></a> Availability Zones for High Availability
  +## <a id='overview'></a> Overview
  +
  +A system with high availability provides higher than typical uptime through redundancy of apps and component VMs. You can create the redundancy required for high availability in several ways, such as running VMs in multiple availability zones and using external blob storage solutions. 
  +
  +The sections in this topic provide guidance on configuring your <%= vars.product_short %> deployment for high availability. 
  +
  +## <a id='high-availability'></a> Components of High Availability Deployments
  +
  +This section describes how you can use availability zones, external load balancers, and external blob storage to ensure high availability for your deployment. 
  +
  +
  +### <a id='azs'></a> Availability Zones
   
   Availability Zones (AZs) are locations where public cloud services offer data centers. 
   
  
positive.code: For more information about scaling applications and maintaining app uptime, see the following topics:
  
  * [Scaling an Application Using cf scale](../devguide/deploy-apps/cf-scale.html)
  *[Using Blue-Green Deployment to Reduce Downtime and Risk](../devguide/deploy-apps/blue-green.html).
  
  ### <a id='vert-scaling'></a> Scale Vertically
  
  
negative.code: 
  <p class="note"><b>Note:</b> Always use an odd number of AZs. This ensures that your deployment remains available when greater than half of the AZs are available. For example, a deployment with three AZs stays available when one AZ goes down and two AZs are still available.</p>
  
  ### <a id='external-lbs'></a> External Load Balancers
  
  External load balancers distribute traffic coming from the internet to your internal network. 
  
  