Add basic docs about nested mode

Related-Bug: 1904488
Change-Id: Id3149e3ee1899d99a6496b90c28033c930ce8232

doc/source/index.rst

@@ -13,6 +13,7 @@ Contents
    :maxdepth: 3
 
    readme
+   nested_vlan_mode
    installation/index
    usage
    contributor/index

doc/source/installation/containerized.rst

@@ -1,3 +1,5 @@
+.. _containerized:
+
 ================================================
 Kuryr installation as a Kubernetes network addon
 ================================================

doc/source/nested_vlan_mode.rst

@@ -0,0 +1,65 @@
+=================================
+Kuryr-Kubernetes nested VLAN mode
+=================================
+
+Kuryr-Kubernetes can work in two basic modes - nested and standalone. The main
+use case of the project, which is to support Kubernetes running on OpenStack
+VMs is implemented with nested mode. The standalone mode is mostly used for
+testing.
+
+This document describes nested VLAN mode.
+
+
+Requirements
+============
+
+Nested VLAN mode requires Neutron to have `trunk` extension enabled, which adds
+trunk port functionality to Neutron API.
+
+
+Principle
+=========
+
+This mode aims at use case of kuryr-kubernetes providing networking for a
+Kubernetes cluster running in VMs on OpenStack.
+
+.. note::
+
+   A natural consideration here is running kuryr-kubernetes in containers on
+   that K8s cluster. For more see :ref:`containerized` section.
+
+The principle of nested VLAN is that Kuryr-Kubernetes will require that main
+interface of the K8s worker VMs is a trunk port. Then each of the pods will
+get a subport of that attached into its network namespace.
+
+
+How to configure
+================
+
+You need to set several options in the kuryr.conf:
+
+.. code-block:: ini
+
+   [binding]
+   default_driver = kuryr.lib.binding.drivers.vlan
+   # Name of the trunk port interface on VMs. If not provided Kuryr will try
+   # to autodetect it.
+   link_iface = ens3
+
+   [kubernetes]
+   pod_vif_driver = nested-vlan
+   vif_pool_driver = nested  # If using port pools.
+
+   [pod_vif_nested]
+   # ID of the subnet in which worker node VMs are running.
+   worker_nodes_subnet = <id>
+
+Also if you want to run several Kubernetes cluster in one OpenStack tenant you
+need to make sure Kuryr-Kubernetes instances are able to distinguish their own
+resources from resources created by other instances. In order to do that you
+need to configure Kuryr-Kubernetes to tag resources with unique ID:
+
+.. code-block:: ini
+
+   [neutron_defaults]
+   resource_tags = <unique-id-of-the-K8s-cluster>