aws-greengrass-nucleus
The Greengrass nucleus is a core component of AWS IoT Greengrass that manages on-device orchestration of deployments and lifecycle management for Greengrass components and applications. It starts, stops, and monitors components and apps, provides interprocess communication between components, and handles component installation and configuration. The nucleus manages a dependency graph of services, each defined by its configuration, dependencies on other services, and a finite state machine representing its lifecycle phases. Dependent services only start after their dependencies, and unstable dependencies trigger notifications to their dependents. The system behaves like a combination of a build tool, a lightweight publish/subscribe messaging system, and a hierarchical key-value store, with configuration changes automatically propagated to all users. Internal connections are managed through dependency injection, and service restarts are handled automatically. The configuration system supports timestamps, valida