.. SPDX-FileCopyrightText: 2023 Gerald Wiese
..
.. SPDX-License-Identifier: GPL-3.0-or-later

One application - multiple systems
==================================

This example automates the deployment of an application split into multiple systems.

It is intended for developers or system administrators who want to investigate on matters of performance or security in case of isolating the services in distinct systems.

The structure of interest looks like this:

.. figure:: ../../graphics/one_application_multiple_systems_1.png

   Components of a service have their separate systems. The directed arrows represent connection requests that still expect responses.


In fact we use a certificate authority (CA) and an Ansible controller but do not want to blow up the number of VMs or containers.
Thus we actually create a structure like this:

.. figure:: ../../graphics/one_application_multiple_systems_2.png
   :width: 70%

   Ansible controller and CA are present as well


`Incus <https://linuxcontainers.org/incus/docs/main/installing/>`_ has to be installed for this example - or the systems have to be created with another tool.
It is used to generate ``db``, ``app`` and ``web`` as containers and ``gui`` as VM:

.. code-block:: console

  $ bash inventories/test/generate_one_app_multi_systems_incus.sh

Log in to ``db``:

.. code-block:: console

  $ incus shell db
  # su debian
  $ cd

First install the requirements as in the first example for Ubuntu but do not run any `ansible-playbook` command.
Then install ``sshpass`` and generate the inventory:

.. code-block:: console

  $ sudo apt install -y sshpass
  $ bash inventories/test/generate_one_app_multi_systems.sh

Now run the playbooks:

.. code-block:: console

  $ ansible-playbook playbooks/gnuhealth.yml -i inventories/test/one_app_multi_systems -e ansible_user=debian -e ansible_ssh_pass='debian' -e ansible_become_pass='debian'
  $ ansible-playbook playbooks/desktop.yml -i inventories/test/one_app_multi_systems -e ansible_user=debian -e ansible_ssh_pass='debian' -e ansible_become_pass='debian'

Then run the client from ``gui`` and verify it is working:

.. code-block:: console

  $ incus console gui --type vga
    -> username: debian, password: debian
  $ startx
    -> Run startx only if not seeing a GUI already
    -> Open client from applications -> office