XenAPI: Add guide document for XenServer

Now we can support OpenStack services deployment on XenServer by
using Kolla. This commit is to amend the document.

Change-Id: I08613c1b77b22cf7d2e695f569497727d3a4c101
blueprint: xenserver-support

doc/source/reference/index.rst

@@ -25,3 +25,4 @@ Projects Deployment References
    skydive-guide
    vmware-guide
    tacker-guide
+   xenserver-guide

doc/source/reference/xenserver-guide.rst

+.. _XenServer-guide:
+
+==================
+XenServer in Kolla
+==================
+
+Overview
+========
+
+Kolla can deploy the OpenStack services on XenServer hosts by choosing
+``xenapi`` as the compute virt driver.
+
+In XenServer, there is a privileged domain which is known as dom0;
+and it can run a number of un-privileged domains which are known as
+domUs or VMs.
+
+Most OpenStack services (e.g. Keystone, Glance, Horizon) can run either
+in the XenServer VMs or in separate baremetal hosts, but some services
+(which make direct use of the hypervisor) must run in the XenServer VMs.
+These services will interact with the XenServer host via XenAPI to perform
+privileged operations. See the following list for such kind of services:
+
+* ``nova-compute``
+
+* ``neutron-openvswitch-agent-xenapi``
+
+* ``ceilometer-compute``
+
+
+.. note::
+
+   At the moment, only CentOS 7.x has been tested.
+
+Preparation for compute node on XenServer hosts
+===============================================
+
+We need some bootstrap tasks particularly for XenAPI compute nodes. The
+tasks are implemented in the package of ``python-os-xenapi`` and exposed
+to kolla-ansible via a single command - ``xenapi_bootstrap``. This package
+is contained in the ``RDO CloudSIG repository`` [`RDO repos`_] and will be
+installed on compute nodes at nova deployment. So we need ensure this
+repository is reachable from the compute nodes or cache the repository
+locally.
+
+Create a compute VM on each XenServer host which will be used to boot
+instances on. The VM must meet the common requirements declared by
+kolla-ansible for KVM/QEMU deployment.
+
+Additionally you should install PV driver in the VM [`XenServer documents`_];
+and create the HIMN(Host Internal Management Network) for each compute VM
+by following these steps:
+
+1. In XenCenter, from the menu choose "View ->  Hidden Objects";
+
+2. You will see HIMN in the host's 'Networking' page;
+
+3. Create an interface on HIMN for the compute VM.
+
+The remaining instructions are just the same as the preparations for
+KVM/QEMU deployment.
+
+Deployment
+----------
+
+Enable the virt type ``xenapi`` and configure connection options in
+``/etc/kolla/globals.yml``:
+
+.. code-block:: yaml
+
+    nova_compute_virt_type: "xenapi"
+    xenserver_username: "root"
+    xenserver_connect_protocol: "https"
+
+.. note::
+
+    When using ``https`` as the connection protocol, please refer XenServer
+    user document to setup the signed SSL certificates to allow the secure
+    communications between dom0 and domU. Otherwise, please use ``http`` for
+    self-signed certificates.
+
+You also need set the password for xenserver_username in
+``/etc/kolla/passwords.yml``:
+
+.. code-block:: yaml
+
+    xenserver_password: "root_password"
+
+Then you can start kolla-ansible deployment just following the general
+deployment instructions [`Quick Start`_].
+
+References
+==========
+
+For more information on XenAPI OpenStack, see:
+
+XenAPI OpenStack: https://docs.openstack.org/nova/latest/admin/configuration/hypervisor-xen-api.html
+
+.. _RDO repos: https://www.rdoproject.org/what/repos/
+
+.. _XenServer documents: https://docs.citrix.com/en-us/xenserver/current-release.html
+
+.. _Quick Start: https://docs.openstack.org/kolla-ansible/latest/user/quickstart.html