+++ /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.
-
-# 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 unneded 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
-
-
-- [Desktop Entry specification](https://www.freedesktop.org/wiki/Specifications/desktop-entry-spec/):
- application enumeration and startup
-
-AGL also provides reference implementations whenever possible and relevant, located in
-the [meta-agl](/3_Developer_Guides/6_AGL_Layers/2_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](/3_Developer_Guides/2_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 promotes the use of [D-Bus](https://www.freedesktop.org/wiki/Software/dbus/)
-as the preferred way for applications to interact with services.
-
-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
-
-# Application launcher service
-
-As mentioned above, the Application Framework follows the guidelines of the
-[Desktop Entry specification](https://www.freedesktop.org/wiki/Specifications/desktop-entry-spec/)
-for application enumeration and startup.
-
-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
-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` is described with more details in [the following document](../2_Application_Startup/).
Code Review / AGL / documentation.git / blobdiff