This topic describes availability zones (AZs) in vSphere and an example of how an operator might scale an app across AZs.

Overview

VMware defines an AZ as an operator-assigned, functionally-independent segment of network infrastructure. In cases of partial infrastructure failure, a tile distributes and balances all instances of running apps across remaining AZs. Strategic use of AZs contributes to the fault tolerance and high availability of a tile deployment.

vSphere supports distributing deployments across multiple AZs. For more information, see Step 4: Create Availability Zones in Configuring BOSH Director on vSphere.

VMware recommends that customers use three AZs to operate a highly available tile deployment.

Balancing Across AZs During Failure: Example Scenario

An operator scales an app to four instances in a tile environment distributed across three AZs: A1, A2, and A3. The environment allocates the instances according to the Diego Auction. For more information about the Diego Auction, see How Diego Balances App Processes.

For a visual representation of this scenario, see the following diagram:

alt-text=A box labeled Your Runtime at the top, and three boxes in a row underneath, labeled A1, A2, and A3. A1 contains two App Instances, while A2 and A3 contain one App Instance each.

If A1 experiences a power outage or hardware failure, the two app instances running in A1 terminate while the app instances in zones A2 and A3 continue to run.

For a visual representation of this scenario, see the following diagram:

alt-text=A box labeled Your Runtime at the top, and three boxes in a row underneath, labeled A1, A2, and A3. A1 contains two App Instances,and both are inactive, while A2 and A3 contain one available App Instance each.

If A1 remains unavailable, the tile balances new instances of the app across the remaining AZs.

For a visual representation of this scenario, see the following diagram:

alt-text=A box labeled Your Runtime at the top, and three boxes in a row underneath, labeled A1, A2, and A3. A1 is still shown as inactive, and it no longer contains App Instances. A2 and A3 contain one available App Instance each.

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