Add info on running Ansible

Author: milliams

source/ansible.rst

@@ -0,0 +1,40 @@
+Running Ansible
+===============
+
+Both the management node and the compute nodes are configured using `Ansible <https://docs.ansible.com/ansible/>`_.
+This is a configuration tool which does things like putting config files in the right place, installing software and creating user accounts.
+The configuration for it is stored on GitHub at `github.com/clusterinthecloud/ansible <https://github.com/clusterinthecloud/ansible>`__
+
+A local clone of the Ansible configuration is made early in the setup of CitC in the folder ``/root/citc-ansible``.
+All further configuration of the system is made in reference to that folder.
+
+Under normal circumstances, you should not have to deal with Ansible manually, but if something goes wrong or you are adding a new feature then you will need this.
+
+Updating Ansible
+----------------
+
+If any bug fixes or new features are added to the version of Ansible on GitHub, they will not automatically become available on your cluster.
+In order to retrieve the changes, you must run:
+
+.. code-block:: shell-session
+
+   $ sudo /root/update_ansible_repo
+
+Configuring the management node
+-------------------------------
+
+The management node is configured automatically by a run of Ansible which is started when the node is first created.
+
+To re-run this manually (for example to retry a failure, or if you've updated the config) you can run:
+
+.. code-block:: shell-session
+
+   $ sudo /root/run_ansible
+
+This will run Ansible in the foreground and also send its output to the usual ``/root/ansible-pull.log`` file.
+
+Compute nodes
+-------------
+
+The same Ansible configuration is used by Packer when creating compute node images.
+The process described under :doc:`node-images` uses this same configuration folder.

source/index.rst

@@ -65,6 +65,7 @@ Once you've got your cluster up and running, see these topics for more informati
    :caption: How-tos
 
    node-images
+   ansible
 
 .. toctree::
    :maxdepth: 1