What is a Mule Domain project and when is it used?

A Mule Domain project is a special project that defines shared configurations (connector configurations, properties) that are reused across multiple Mule applications deployed to the same Mule runtime instance (on-premises or Runtime Fabric). Use cases:

1. Share an HTTP Listener configuration (same port) across multiple applications — without a domain, each application needs its own port.
2. Share database connection pools, JMS brokers, or other expensive resources.
3. Share property placeholder files across applications. Limitations: Domains are only supported on standalone (on-premises) Mule runtimes and Runtime Fabric — CloudHub does not support multi-application domains (each CloudHub app is isolated). In CloudHub, resource sharing is achieved through VM connector queues, Anypoint MQ, or database-level sharing. Domain projects are deployed independently and must be deployed before the applications that reference them.