Policies, principles and basic concepts

A ‘release unit’ describes the portion of a service or IT infrastructure that is normally released  together according to the organization’s release policy. The unit may vary, depending on the type(s) or item(s) of service asset or service component such as software and hardware. Figure 4.15 gives a simplified example showing an IT service made up of systems and service assets, which are in turn made up of service components

Simplified example of release units for an IT service

The general aim is to decide the most appropriate release-unit level for each service asset or component. An organization may, for example, decide that the release unit for business critical applications is the complete application in order to ensure that testing is comprehensive. The same organization may decide that a more appropriate release unit for a website is at the page level.
The following factors should be taken into account when deciding the appropriate level for release units: · The ease and amount of change necessary to release and deploy a release unit · The amount of resources and time needed to build, test, distribute and implement a release unit · The complexity of interfaces between the proposed unit and the rest of the services and IT infrastructure · The storage available in the build, test, distribution and live environments. Releases should be uniquely identified according to a scheme defined in the release policy as discussed in section 4.1.4.2. The release identification should include a reference to the CIs that it represents and a version number that will often have two or three parts, e.g. emergency fix releases: Payroll_System v.1.1.1, v.1.1.2, v.1.1.3.

Release design options and considerations

Service Design will define the approach to transitioning from the current service to the new or changed service or service offering. The SDP defines the service and solution design components to be transitioned to deliver the required service package(s) and service level package(s). Common options for release and deployment that are considered in Service Design are discussed below. The selected option will have a significant impact on the release and deployment resources as well as the business outcomes. It isimportant to understand the patterns of business activity (PBA) and user  profiles when planning and designing the releases.