An application that can be ordered. It is automatically provisioned, can be consumed by a service consumer and generally adheres to our quality requirements.

Service Consumer

An application that connects to a service instance as a client.

Service Order

The act of deploying a Kubernetes resource that triggers the provisioning of a new service instance.

Service Instance

A single isolated occurrence of a service.

Cloud Instance

An instance of a cloud service offering by a cloud service provider.

Converged Service Instance

An instance of a converged service blueprint. Either in the same namespace as the service order was made or in another namespace.

Service Location

Services can be provisioned on various places:

Converged Cluster

Service instance runs on the same cluster as the service consumer.

Service Cluster

Service runs on one or more dedicated clusters, reserved for services.

Cloud Service

A type of service architecture offered by a cloud service provider such as AWS or GCP.

Converged Service

A type of service developed to run on a converged cluster.

Converged Service Architectures

Architecture refers to the deployment strategy of a service instance in relation to high availability.


A single node instance without any high availability.


The service offers data replication to one or more other instances.


A fully clustered version of the service, usually offering active / active replication with fully automated cluster handling.


Service User

A human that interacts with AppCat.

Service Maintainer

A human that engineers and maintains a service (code).

Service Engineer

A human that performs day-2 operations or resolves incidents.

Framework Maintainer

A human that engineers and maintains the framework (code).


A Composition refers to the key Crossplane API type that configures how Crossplane should compose resources into a higher level "composite resource". A Composition tells Crossplane "when someone creates composite resource X, you should respond by creating resources Y and Z".

Composite Resource

A "Composite Resource" or "XR" is an API type defined using Crossplane. A composite resource’s API type is arbitrary - dictated by the concept the author wishes to expose as an API. A common convention is for types to start with "X" - for example "XAcmeCoDB".

A composite resource can be thought of as the interface to a Composition. It provides the inputs a Composition uses to compose resources into a higher level concept. In fact, the composite resource is the high level concept.

Composite Resource Definition (XRD)

A "Composite Resource Definition" or "XRD" is the API type used to define new types of composite resources and claims. Types of composite resources and types of claims exist because they were defined into existence by an XRD. The XRD configures Crossplane with support for the composite resources and claims that make up a platform API.

Composite Resource Claim (XRC, claim)

Each claim corresponds to a composite resource, and the pair have nearly identical schemas.

In the context of AppCat, a resource claim is created in the user’s namespace, which binds a cluster-scoped composite resource.