+++ /dev/null
----
-title: Introduction
----
-
-# Foreword
-
-The AGL Application Framework is nothing new. However, the implementation used
-up until the `lamprey` release has been retired starting with the `marlin`
-release and replaced by a redesigned Application Framework one. However, this
-new implementation isn't a 1:1 replacement, and as such it doesn't provide all
-of the features of the previous Application Framework. Some of those will be
-added back over time, others have been discarded in favor of more modern and/or
-widely-used alternatives.
-
-With the `needlefish` release, further changes have been added, including a
-[gRPC IPC](https://grpc.io/about), alongside a deprecated D-Bus one, as well as
-using as using systemd units as opposed on using
-[Desktop Entry specification](https://www.freedesktop.org/wiki/Specifications/desktop-entry-spec/)
-to list applications, and relies entirely on systemd to start application,
-rather than spawning them directly.
-
-Once all platforms transitioned to gRPC, the D-Bus functionality will be
-removed entirely, mentioning it in only in documentation for history purposes.
-
-# Introduction
-
-As a provider of an integrated solution to build up on, AGL needs to define a
-reliable and well-specified method for managing the deployment and integration
-of applications and services, as well as the way they can interact with the
-rest of the system.
-
-This is achieved by providing a common set of rules and components, known as
-the Application Framework. By ensuring conformity to those rules, application
-developers can have a good understanding of the requirements for creating and
-packaging applications targeting AGL-based systems. Likewise, system developers
-and integrators have a clear path for including such applications in AGL-based
-products.
-
-The Application Framework's scope extends to the following areas:
-- system services integration and lifecycle management
-- user session management, including user-level applications and services
- lifecycle management
-- inter-process communication
-
-In order to be as simple as possible and avoid any unneeded custom
-implementation, the Application Framework relies mainly on third-party
-technologies and/or software components, most of those being maintained under
-the [freedesktop.org](https://www.freedesktop.org) umbrella. Those include:
-
-
-- [systemd](https://www.freedesktop.org/wiki/Software/systemd/): system
- services and user session services management
-
-
-- [D-Bus](https://www.freedesktop.org/wiki/Software/dbus/): inter-process
- communication, with `needlefish' release deprecated phase.
-
-- [gRPC](https://grpc.io/about): inter-process communication, new recommmended
- system-wide IPC, which should be used instead of D-Bus.
-
-
-- [Desktop Entry specification](https://www.freedesktop.org/wiki/Specifications/desktop-entry-spec/):
- application enumeration and startup, now in deprecated phase, systemd being
- the one would list out applications and handling start-up.
-
-AGL also provides reference implementations whenever possible and relevant,
-located in the [meta-agl](/04_Developer_Guides/02_AGL_Layers/02_meta_agl/)
-layer under `meta-app-framework`. At the moment, the Application Framework
-contains 2 such components:
-
-- `agl-session`: `systemd` unit files for user sessions management
-
-- `applaunchd`: application launcher service
-
-# Services management
-
-Both system and user services are managed by `systemd`, which provides a number
-of important features, such as dependency management or service monitoring:
-when starting a service, `systemd` will ensure any other units this service
-depends on are available, and otherwise start those dependencies. Similarly,
-`systemd` can automatically restart a crashed service, ensuring minimal
-downtime.
-
-`systemd` also provides an efficient first layer of security through its
-[sandboxing](https://www.freedesktop.org/software/systemd/man/systemd.exec.html#Sandboxing)
-and other security-related options.
-
-It is also well integrated with D-Bus and can be used for a more fine-grained
-control over D-Bus activated services: by delegating the actual service startup
-to `systemd`, developers can take advantage of some of its advanced features,
-allowing for improved reliability and security.
-
-Each service should be represented by a `systemd` unit file installed to the
-appropriate location. More details can be obtained from the [Creating a New
-Service](../03_Creating_a_New_Service/) document.
-
-# User session management
-
-Similarly, user sessions and the services they rely on are also managed by
-`systemd`.
-
-AGL provides 2 `systemd` units:
-
-
-1\. `agl-session@.service` is a template system service for managing user
-sessions; it takes a username or UID as a parameter, creating a session for the
-desired user. Instanciating this service can be achieved by enabling
-`agl-session@USER.service`, for example by executing the following command on a
-running system:
-
-```
-$ systemctl enable agl-session@USER.service
-```
-
-By default, AGL enables this service as `agl-session@agl-driver.service`,
-running as user `agl-driver`.
-
-*Note: while you can create sessions for as many users as needed, only one
-instance of `agl-session@.service` is allowed per user.*
-
-
-2\. `agl-session.target` is a user target for managing user services and their
-dependencies. It is started by `agl-session@.service`.
-
-By default, `agl-compositor` is part of this target. It is therefore
-automatically started for user `agl-driver`.
-
-Any other service needed as part of the user session should similarly depend on
-this target by appending the following lines to their unit file:
-
-```
-[Install]
-WantedBy=agl-session.target
-```
-
-# Inter-process communication
-
-In order to provide a "standard", language-independent IPC mechanism and avoid
-the need for maintaining custom bindings for each programming language to be
-used on top of AGL, the Application Framework used to promote the use of
-[D-Bus](https://www.freedesktop.org/wiki/Software/dbus/) as the preferred way
-for applications to interact with services. Starting with `needlefish` release,
-we instead switched to using [gRPC](https://grpc.io) for our system-wide IPC,
-with D-Bus being kept to provide functionality to services and application
-which haven't transitioned yet to using gRPC.
-
-Most services already included in AGL provide one or several D-Bus interfaces,
-and can therefore interact with D-Bus capable applications and services
-without requiring any additional component. Those services include, among
-others:
-
-- [ConnMan](https://git.kernel.org/pub/scm/network/connman/connman.git/):
- network connectivity
-
-- [BlueZ](http://www.bluez.org/): Bluetooth connectivity
-
-- [oFono](https://git.kernel.org/pub/scm/network/ofono/ofono.git): telephony
- and modem management
-
-- [GeoClue](https://gitlab.freedesktop.org/geoclue/geoclue/-/wikis/home):
- geolocation
-
-Similarly, we're in the phase of expanding various services to expose a
-gRPC interface.
-
-# Application launcher service
-
-The Application Framework used to follow the guidelines of the [Desktop Entry
-specification](https://www.freedesktop.org/wiki/Specifications/desktop-entry-spec/)
-for application enumeration and startup, but with the `needlefish` release
-instead it relies on systemd to provide that functionality, indirectly, by
-using the `applaunchd` application.
-
-As no simple reference implementation exists for this part of the
-specification, AGL provides an application launcher service named `applaunchd`.
-This service is part of the default user session, and as such is automatically
-started on session startup. It can therefore be considered always available.
-
-`applaunchd` enumerates applications installed on the system and provides a
-D-bus (deprecated)/gRPC interface for services and applications to:
-- query the list of available applications
-- request the startup and/or activation of a specific application
-- be notified when applications are started or terminated
-
-`applaunchd` with the D-Bus interface is described with more details in
-[the following document](../02_Application_Startup_Dbus/).
Code Review / AGL / documentation.git / blobdiff