Usage modes
===========

The REDAC system is still in development, and thus are the usage modes.
Despite we have a single user mode in mind which solely goes via a single
entrypoint, which does scheduling, load balancing and the like, in special
situations a number of different usage modes are supported in the moment.
A graphical overview in a block schema diagram is provided in
:numref:`fig-usage-modes` and subsequentialy discussed.

.. _fig-usage-modes:
.. figure:: drawings/usage-modes.png
   :alt: schema drawing
   :width: 60%

   The different inofficial user access variants for REDAC

Queue access
------------

The primary access is indirected by the :ref:`redaccess` via HTTP and
REST. This way, ordinary encrypted HTTPS can be used and the regular
:ref:`opauth` methods can be employed. Therefore, this access method is the
only one which is advertised in the REDAC user manual.


Immediate SuperController access
--------------------------------

The immediate mode access to the :ref:`pybrid` is technically only possible
when being within the :ref:`opnetwork`. This is for instance possible via
a VPN solution or with appropriate firewall rules from outside. It is
important to note that in this mode, no user authentification is applied,
computing time is not accounted and the TCP connection to the SuperController
is not encrypted. Furthermore, the protocol is no more HTTP but the specific
JSONL protocol which is documented in the pybrid and firmware documentations.

This immediate mode can be interesting for debugging, for experienced users,
in particular single system users. Users are suggested to use the ``pybrid``
python package to connect to the pybrid proxy.

Immediate Microcontroller access
--------------------------------

In this variant, even the SuperController is short-circuited and users
directly access the mREDAC-embedded microcontrollers. This is possible if
users are part of the :ref:`opnetwork` (see previous section). However, as
a drawback to the immediate SuperController access, in this mode users
can not make use of the global synchronization line. That means that
synchronized computations accross more then a single mREDAC are not possible.

This kind of access is strongly discouraged whenever any part of the higher
level software abstraction is active, i.e. even if the pybrid proxy is active.
If users want to make use of this access mode, they should use the ``pybrid`` or
``lucipy`` sofware packages in order to address the mREDAC boards.

JupyterHub/Browser access
-------------------------

JupyterHub is a hosted computation software provided by :ref:`opanabrid`.
It is basically a hybrid mode which allows all kind of uses. It combines
a number of advantages:

- User does not need to install any software/development environment locally.
  He finds the open source scientific programming environment *jupyter* readily
  available in browser, comparable to Matlab.
- Regular queue access is possible
- However, also direct access is possible if neccessary since the instance
  has access to the REDAC internal network.