What Is a TOSCA Template?

Topology and Orchestration Specification for Cloud Application (TOSCA) is an OASIS open standard that defines the interoperable description of services and applications hosted in the cloud, thereby facilitating lifecycle management across cloud service providers. Figure 1 shows the application topology model used by AOS.

Figure 1 Application topology model

**Table 1** Elements and relationships in the application topology model
Element	Description
Resource	Resources, including virtual machines (VMs) and containers.
AppGroup	A group of one or more cloud applications. You can perform lifecycle management (such as deployment and upgrade) for the entire group rather than for individual cloud application. A cloud application group can be a customer product, service system, or subsystem.
Application	Cloud application running on resources. It is the smallest deployable object in the application topology model. Note that a microservice is a type of application.
SoftwareComponent	Software component of a cloud application. Each component is packed into a software package. This element is optional and can also be an attribute of the Application element.
Service	Service on which an application depends. A service is a set of function objects.
DependsOn	A relationship describing dependencies between elements, which determines the sequence in which elements will be created.
HostedOn	A relationship describing that applications run on resources.
ConsistsOf	A relationship of composition. For example, AppGroup consists of applications.
ConnectsTo	A relationship describing that one element calls or connects to another element. For example, applications or resources connect to each other.
PackageConsistsOf	A relationship describing that an application consists of software components.