Updated k8s description

source/technical.rst

@@ -24,31 +24,35 @@ functionality:
 * VO-Specific storage/Big data facilities or any pluggable tools into the
   notebooks environment can be added to community specific instances.
 
-
 .. [[File:EGI_Notebooks_Stack.png|center|650px|EGI Notebooks Achitecture]]
 
-Kubernetes usage
-::::::::::::::::
+Kubernetes
+::::::::::
 
 A Kubernetes (k8s) cluster deployed into a resource provider is in charge of
 managing the containers that will provide the service. On this cluster there are:
 
 * 1 master node that manages the whole cluster
 
-* 1 or more edge nodes with a public IP and corresponding public DNS name
-  (notebooks.egi.eu) where a k8s ingress HTTP reverse proxy redirects requests
-  from user to other components of the service. The HTTP server has a valid
-  certificate from one CA recognised at most browsers (e.g. DigiCert).
+* Support for load balancer or alternatively 1 or more edge nodes with a
+  public IP and corresponding public DNS name (e.g. notebooks.egi.eu) where
+  a k8s ingress HTTP reverse proxy redirects requests from user to other
+  components of the service. The HTTP server has a valid certificate from
+  one CA recognised at most browsers (e.g. Let's Encrypt).
 
 * 1 or more nodes that host the JupyterHub server, the notebooks servers where
   the users will run their notebooks. Hub is deployed using the
-  `JupyterHub helm charts <https://jupyterhub.github.io/helm-chart/>`_.
+  `JupyterHub helm charts <https://jupyterhub.github.io/helm-chart/>`_. These
+  nodes should have enough capacity to run as many concurrent user notebooks as
+  needed. Main constraint is usually memory.
 
-* Persistent storage managed via NFS to be exposed into the notebooks as
-  user space.
+* Support for `Kubernetes PersistentVolumeClaims <https://kubernetes.io/docs/concepts/storage/persistent-volumes/>`_
+  for storing the persistent folders. Default EGI-Notebooks installation
+  uses NFS, but any other volume type with ReadWriteOnce capabilities can be
+  used.
 
-* Prometheus allows monitoring of usage of resources and it's queried by the
-  accounting plugin to produce accounting records.
+* Prometheus installation to monitor the usage of resources so accounting
+  records are generated.
 
 All communication with the user goes via HTTPS and the service only needs a
 publicly accessible entry point (public IP with resolvable name)