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The assembly model specification 2 deals briefly with distributed runtimes in its discussion of SCA Domains
"An SCA Domain represents a complete runtime configuration, potentially distributed over a series of interconnected runtime nodes."

The assembly spec, however, is not prescriptive about how an SCA Domain should be mapped and supported across multiple runtime nodes. Here I believe the term runtime node (or just node) is used to describe a process running an SCA runtime in which components can be run, e.g. the Java or C++ runtimes that Tuscany is developing.

Motivation

Some reasons for distributing a domain

1. Represent the widely distributed nature of a typical SOA so that SCA presents a cross enterprise description of assembled components
2. Policy matching where components require particular resources and hence particular, and separate, nodes
3. HA/Load balancing/Performance scenarios where a single component appears on multiple nodes
4. Load balancing/Performance scenarios where domian si spread across multiple nodes (same as 1 & 2)

Terminology

SCADomain, Composite, Component, Service, Reference - as used in SCA

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Component Instance - The running component that services requests. A single component definition in a SCDL file may give rise to one or more component instances depending on how the component is scoped (using the @Scope annotation).

Scenarios

1. Starting a runtime

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Starting a runtime (collection of nodes) will be a manual task. This task could be automated in the future with some scheduling/provisioning system that is able to select appropriate processors for runtime execution.

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