add explanation about component containers.

Signed-off-by: Tomoya.Fujita <Tomoya.Fujita@sony.com>

source/Concepts/Intermediate/About-Composition.rst

@@ -33,6 +33,27 @@ By making the process layout a deploy-time decision the user can choose between:
 
 Additionally ``ros2 launch`` can be used to automate these actions through specialized launch actions.
 
+Component container
+-------------------
+
+Component container is a host process that allows you to load and manage multiple components at runtime within the same process space.
+This enables better performance and memory efficiency because it avoids inter-process communication overhead when nodes interact.
+
+As of now, these are generic component container types available.
+
+* `component_container <https://github.com/ros2/rclcpp/blob/{REPOS_FILE_BRANCH}/rclcpp_components/src/component_container.cpp>`__
+  * The most generic component container that uses a single ``SingleThreadedExecutor`` to execute all components including component container itself.
+
+* `component_container_mt <https://github.com/ros2/rclcpp/blob/{REPOS_FILE_BRANCH}/rclcpp_components/src/component_container_mt.cpp>`__
+  * Component container that uses a single ``MultiThreadedExecutor`` to execute the components including component container itself.
+  * ``thread_num`` parameter option is available to specify the number of threads in ``MultiThreadedExecutor``.
+
+* `component_container_isolated <https://github.com/ros2/rclcpp/blob/{REPOS_FILE_BRANCH}/rclcpp_components/src/component_container_isolated.cpp>`__
+  * Component container with dedicated either ``SingleThreadedExecutor`` (default) or  ``MultiThreadedExecutor`` executors for each component. (Component container is executed by ``SingleThreadedExecutor``) 
+  * ``--use_multi_threaded_executor`` argument specifies executor type used for each component to ``MultiThreadedExecutor``.
+
+See more details for :doc:`Types of Executors <../Concepts/About-Executors#types-of-executors>`.
+
 Writing a Component
 -------------------
 

source/Tutorials/Intermediate/Composition.rst

@@ -210,6 +210,29 @@ Advanced Topics
 
 Now that we have seen the basic operation of components, we can discuss a few more advanced topics.
 
+Component container types
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+As introduced in :doc:`Component container <../../Concepts/About-Composition#component-container>`, there is a few component container types with options.
+You can choose the most appropriate component container type for your requirement.
+
+* ``component_container`` (No options / parameters available)
+
+.. code-block:: bash
+
+   ros2 run rclcpp_components component_container
+
+* ``component_container_mt`` with ``MultiThreadedExecutor`` composed of 4 threads.
+
+.. code-block:: bash
+
+   ros2 run rclcpp_components component_container_mt --ros-args -p thread_num:=4
+
+* ``component_container_isolated`` with ``MultiThreadedExecutor`` for each component.
+
+.. code-block:: bash
+
+   ros2 run rclcpp_components component_container_isolated --use_multi_threaded_executor
 
 Unloading components
 ^^^^^^^^^^^^^^^^^^^^