A deployment diagram serves to model the physical deployment of artifacts on deployment targets.
It shows "the allocation of Artifacts to Nodes according to the Deployments defined between
them."
Deployment of an artifact to a node is indicated by placing the artifact inside the node. Instances
of nodes (and devices and execution environments) are used in deployment diagrams to indicate
multiplicity of these nodes. For example, multiple instances of an application server execution
environment may be deployed inside a single device node to represent application server clustering.