Why Should I Fence Configurations; How Does Fencing Work - VMware VLM3-ENG-CP - Lab Manager - PC User Manual

VMware® Lab Manager User's Guide
Why Should I Fence Configurations?
Typically, you want to enable network fencing under these circumstances:
You have a configuration with one or more servers, and you anticipate cloning the
configuration numerous times.
You have a configuration involving a difficult and complex setup, and cloning the
configuration is an easier route than repeating the setup.
With fencing, engineers can run multiple, independent tests on a configuration
deployed multiple times. Fencing is particularly useful when a developer needs to
examine a bug without interrupting or stopping ongoing testing on a configuration.
Lab Manager also enables you to reproduce the bug at a later time if the developer is
unavailable.
The default number of concurrently deployed fenced configurations on a Managed
Server system is 20. If you need more configurations, you can increase the number
without any penalty.
From a performance perspective, network fencing impacts the traffic flow between
modules. Fencing requires a slightly higher number of resources on the Managed
Server system, such as memory, CPU, networking, and virtual machine slots. If you
enable fencing but never use it, these resources do not come into play.
How Does Fencing Work?
Virtual machines in a configuration have preconfigured (internal) IP addresses. When
you deploy virtual machines in fenced mode, Lab Manager assigns a unique external
IP address to each of these machines. Through these external addresses, virtual
machines both inside and outside the fence can communicate with each other. Lab
Manager uses a virtual router to route packets between these virtual machines. Lab
Manager configures the virtual router when you deploy a fenced configuration and
deletes it when you undeploy the configuration.
Figure C‐1 illustrates configurations without fencing and with fencing.
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