An external store should be used for Mule application state when persistence, distributed access, scalability, and synchronization across multiple instances are necessary for consistent application behavior.
You should use an external store to store and manage Mule application state in scenarios where the state needs to be shared across multiple instances for scalability, or retained in the event of application restarts due to updates or crashes. State management is crucial for applications that require consistent behavior in distributed systems. Such external storages will include databases, cache stores, or cloud storage services depending on the nature of the state and the performance requirements.
For instance, in e-commerce applications where cart information needs to be consistent across devices and sessions, an external database would be appropriate. In the case of high-throughput applications that require fast read/write operations, a distributed cache like Redis might be leveraged. In microservices architectures, where Mule applications often operate, external state management ensures that state is not lost when individual services are scaled or updated, thus maintaining the integrity of business processes and transactions.
An external store becomes essential when persistence, resilience, distributed access, and synchronization of application state are required to meet the system's demands.