Components

This section contains documentation about components in the new component framework (components v2).

Components are the basic unit of executable software on Fuchsia.

Note: The component framework is under active development. This document only covers the new architecture (components v2) implemented by component_manager. The old architecture (components v1) implemented by appmgr is still in use but will be removed once the transition to the new architecture is complete.

Architectural concepts

• Introduction: What are components and the component framework.
• Component manager: The runtime.
• Declarations: Describe components themselves.
• Component URLs: URLs that identify components.
• Lifecycle: Component instance progression from creation to destruction.
• Topology: The relationships among component instances.
• Realms: Sub-trees of the component instance topology.
• Monikers: Identifiers for component instances based on the component topology.
• The difference between components and processes: The relationship between components and processes.

Developing components

• Capabilities: Different types of capabilities and how to route them between components.
• Component manifests: How to define a component for the framework.
• ELF runner: How to launch a component from an ELF file. Typically useful for developing system components in C++, Rust, or Go.

Extending the component framework

• Runners: Instantiate components; add support for more runtimes.
• Resolvers: Find components from URLs; add support for methods of software packaging and distribution.

Debugging and troubleshooting

• Hub: A live view of the component topology at runtime.
• OpaqueTest: Hermetic testing framework.

Internals

• Design principles: Guidelines for arriving at architectural decisions.
• Life of a protocol open: How components connect to protocols in their namespaces.