Cluster: helps running and coordinating several Node processes:
- API.
- Module to get started easily: cluster-master.
Domains: help keeping your Node process up and running by catching unhandled errors:
- API.
- Read the example code to understand the basic workflow of domains.
- Module to get started easier: domain-http-server.
Many Node projects start using domains and clusters, including npm site itself (source code is available on GitHub).