Components v2

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.
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.

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.

Components (either version)

Component URLs are URLs that identify components.
Components vs. processes: how the concepts differ

Testing

Test components: defining components that implement tests and running them.
Test Runner Framework: writing idiomatic tests in different languages that use common testing frameworks.
Complex topologies and integration testing: testing interactions between multiple components in isolation from the rest of the system.

Internals

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