Integrate podman in Oniro

Closes #19 (closed) #20 (closed)

docs/supported-technologies/containers.rst

+.. SPDX-FileCopyrightText: Huawei Inc.
+..
+.. SPDX-License-Identifier: CC-BY-4.0
+
+.. include:: ../definitions.rst
+
+Containers
+##########
+
+|main_project_name| maintains support for a container-based architecture
+included as part of the OS when using the reference images (or images derived
+from them).  This OS functionality aims at facilitating the deployment of
+container-based applications. This feature plays a part in the wider
+|main_project_name| update software stack for managing deployments and updates
+from the host operating system to the container-based applications.
+
+.. note::
+
+    The current support is aiming at the Linux-based |main_project_name| images.
+
+As part of this architecture, |main_project_name| currently provides the
+integration and support for the following container management engines:
+
+Podman
+********
+
+`Podman <https://podman.io/>`_ is a daemonless container engine that can run
+both in root and rootless mode. |main_project_name| supports both of these
+modes while keeping the read-only root filesystem assumption valid by taking
+advantage of the application partition for storing persistent data.
+
+The OS integration provides seamless integration with `docker` CLI  so that
+`docker` commands are handled transparently by `podman`.
+
+When using `podman` alone, deploying a service is as simple as running the
+associated CLI command for spawning a container of a specific image. For
+example, running a `busybox` container using an image from `dockerhub`
+container registry is achieved by running the following when logged in as the
+`oniro` user:
+
+.. code-block:: console
+
+    $ podman run -ti --rm docker.io/library/busybox:latest ls
+
+This will spawn, run and remove a `busybox` rootless container. You can run the
+same example in root mode:
+
+
+.. code-block:: console
+
+    $ sudo podman run -ti --rm docker.io/library/busybox:latest ls
+
+Updating a containerised application, when using `podman` alone follows the
+classic container flow:
+
+  * stop container
+  * update/pull image
+  * start a new container
+
+As an example, we use the same container image above running a tool in
+background mode:
+
+.. code-block:: console
+
+    # run a container in background
+    $ podman run -d --name busybox_top docker.io/library/busybox:latest top
+      8fcc484d8a905a9e6cb24e1eac87782970f91951ab1cb0d1b0ec64729e0ffb01
+
+    # the container is running
+    $ podman ps
+      CONTAINER ID  IMAGE                             COMMAND     CREATED        STATUS            PORTS       NAMES
+      8fcc484d8a90  docker.io/library/busybox:latest  top         6 seconds ago  Up 4 seconds ago              busybox_top
+
+    # stop the container
+    $ podman stop busybox_top
+      busybox_top
+
+    # pull an updated container image
+    $ podman pull docker.io/library/busybox:latest
+      Trying to pull docker.io/library/busybox:latest...
+      Getting image source signatures
+      Copying blob 19d511225f94 skipped: already exists
+      Copying config 62aedd01bd done
+      Writing manifest to image destination
+      Storing signatures
+      62aedd01bd8520c43d06b09f7a0f67ba9720bdc04631a8242c65ea995f3ecac8
+
+    # run the updated container
+    $ podman run -d --name busybox_top_update docker.io/library/busybox:latest top
+      1a3a7383a111e79b702fd081d4204a5827698b252d2d00ee9ae818306dbbef87
+
+    # check that the updated container is running
+    $ podman ps
+      CONTAINER ID  IMAGE                             COMMAND     CREATED        STATUS            PORTS       NAMES
+      1a3a7383a111  docker.io/library/busybox:latest  top         8 seconds ago  Up 5 seconds ago              busybox_top_update
+
+    # cleanup
+    $ podman stop busybox_top_update
+    $ podman rm busybox_top busybox_top_update
+
+The output above may be slightly different due to variations in your local
+setup. That is expected.