Figure 6.9 The default tiering options for a new service template. You’ll see that a
three-tier application is also available if you scroll down.
Web applications (Web Deploy) and database applications (SQL DAC) are considered
first class in service templates, because service templates understand the Metadata of
these types of applications and can enable parameters to perform the configuration
when the application is deployed, such as by the end user. Other types of application
installs are fully supported through the service template Generic Command Execution
(GCE) feature because many organizations are not using SQL DAC, Server App-V, or
maybe even Web Deploy yet. By using GCE, you can run both pre- and post-scripts for
any type of application installation. The customization of non-first-class applications
would need to be done through the application’s native unattended configuration
capabilities or scripting and would not integrate with the service deployment interface
in the same way as first-class applications do. Standard Windows Server roles and
features can also be added through standard virtual machine guest OS definitions.
A minimum, maximum, and initial number of instances of each tier are specified,
which allows for easy scale out and scale in, depending on utilization. Service
instances created from a service template maintain a link back to the template, and
that template becomes read-only, so it becomes the source of truth for how the service
looked. If an update is required, a new version of the service template is created and
that updated service template is applied to deployed instances. The deployment of the
new service template version will update the services while maintaining the
application state through the Server App-V state backup and restore feature.
The use of services enables fewer OS images to be managed by the IT department
because of the abstraction of the actual services, roles, features, and applications
needed on the operating system, which traditionally may have been part of the OS