image. Services also enable the related VMs to be treated as a single unit. Another nice
bonus feature is that if SCVMM is integrated with Operations Manager, then
Operations Manager will understand the service definition and show the VMs as part
of a service.
A four-stage life cycle is the focus for service templates, to which I’ve previously
alluded:
1 . Create the service template.
2 . Customize the deployment at the deployment time of the service template.
3 . Deploy the service to environments.
4 . Update the service template to a new version, and apply it to running instances of
the service.When an update to an existing instance of a service is made, there are three update
types. The first type is a settings-only update mode, which only changes application
settings but does not replace the OS image. The second update type is new, an in-place
update; updates to the template settings are applied, but the actual OS images are not
replaced. This would be used to update applications and modify configuration of the
virtual machines in the service. The last type is the image-based update, which
replaces the actual deployed instance operating system images with the new OS image
and performs a reinstallation of applications but maintains the application state. If
you have modified a virtual machine configuration that is part of a service, for
example, and you changed the memory from 1GB to 4GB and then applied an update
to the service from a new version of the service template, then any customizations you
made to the configuration would be lost. Remember, with services, the service
template is always the source of truth. This can be useful, for example, if your service
instance has lost some VMs and you want to bring it back within the parameters of the
service template. Instances can be refreshed from the service template, which will
look for any missing elements of tiers that have less than the minimum number of
instances and fix them by deploying additional required VMs.
In addition to allowing the definitions of virtual machine templates to use,
applications to install, and various other settings, it is within a service template that
you can also utilize load balancers and logical networks. By using the other fabric
elements, service templates can enable rich capabilities in a completely automated
fashion.
Service templates are created and maintained in the Service Template Designer, which
is shown in Figure 6.10, and consists of the familiar ribbon, a designer canvas (which
is the majority of the interface), and a small properties area at the bottom that shows
the properties of the currently selected object. Once configurations are made, you run
the Save And Validate action, which checks for any problems in the service template
definition.