Containers

enzoaguado · July 27, 2023, 6:52am

Containers are the centre piece of the Anbox Cloud stack. Every time you launch an application or an image, Anbox Cloud creates a container for it. Every container provides a full Android system.

All containers in Anbox Cloud are ephemeral, which means that as soon as a container is stopped, all of its data is deleted. Anbox Cloud DOES NOT back up any data from the Android or the outer Ubuntu container. Backup and restore of data must be implemented separately through addons. See Example: Back up data for information on how to do this.

Regular containers vs. base containers

Anbox Cloud differentiates between two types of containers: regular containers and base containers. The container type is visible in the output of the amc ls command.

Regular containers are containers that are launched from either an application or an image. They exist until they are deleted.

Base containers are temporary containers that are used when bootstrapping an application. They are automatically deleted when the application bootstrap is completed.

When we refer to containers in this documentation without specifying the container type, we mean regular containers.

Application containers vs. raw containers

Containers are based on either applications or images. That means that if you launch an application or an image, Anbox Management Service (AMS) automatically creates a container for it.

Application containers are containers created when launching an application and run the full Android system. If the application is based on an Android app (an APK package), this app is launched after the system boots and monitored by the watchdog. With the default configuration, you will see only the app and not the Android launcher.

Raw containers are containers created when launching an image. They run the full Android system, without any additional apps installed.

Container life cycle

Creating a container

When you create a container by either launching or initialising an application or an image, AMS schedules the container on a LXD node. The container then executes the following steps in order:

Configure the network interface and gateway.
(Only for raw containers) Install addons that are specified with --addons.
Expose services that are specified with --service or through the application manifest.
Execute the pre-start hook provided by the installed addons.
Launch the Android container.
Execute the post-start hook provided by the installed addons.

Container start

The container launch process is successful only if all of the above steps succeed. If there are issues during the process, the status of the container changes to the error status. You can view the available logs from the container for further troubleshooting.

Stopping a container

Containers can be stopped because of the following scenarios:

You stopped it.
You deleted it.
An error occurred.

When a container is stopped, it executes the following steps in order:

Stop the Android container.
Execute the post-stop hook provided by the installed addons.
Shut down the container.

Beyond that, the container will be removed from AMS either because you deleted it or because an error occurred during its runtime.
Container stop

Possible container status

A container moves through different stages and correspondingly have the following status depending on its current state.

Status	Description
`created`	AMS has created an internal database object for the container and will next schedule the container onto a suitable LXD node.
`prepared`	AMS has decided the LXD node on which it will schedule the container.
`started`	The container is started and now booting. During the boot sequence, possible hooks are executed. Only when all hooks have been executed, the container will switch to `running`.
`running`	The container is fully up and running.
`stopped`	The container is fully stopped and will be deleted by AMS.
`deleted`	The container is deleted and will be removed from the AMS database soon.
`error`	An error occurred while processing the container. The container is stopped. Further information about the error can be viewed with `amc show <container id>`.

Development mode

AMS allows to start a container in development mode. This mode turns off some features that are usually active in a container. It is mainly useful when developing addons inside a container.

When development mode is enabled, the container sends status updates to AMS when the Anbox runtime is terminated, however, AMS allows the container to continue running. This allows you to restart the Anbox runtime inside the container, providing an easy way to test addons or develop a platform plugin.

To check whether development mode is enabled, run amc show <container_ID> or look at the /var/lib/anbox/session.yaml file in the container. If the devmode field in the configuration file is set to true, development mode is active.