Multitier Architecture
""""""""""""""""""""""

Multitier Architeture e.g ``web`` & ``db``

Manage Host Groups
------------------
* a good solution is to create a parent-group for an application
* the tiers are ``children`` of the application group

.. code-block:: yaml

    # file: hosts
    [flask_web]
    web1.pascal.lab

    [flask_db]
    db.pascal.lab

    [flask_app:children]
    flask_web
    flask_db

Now we've got these groups:

* flask_web
* flask_db
* flask_app


Setting variables for tiers
---------------------------
* variables for both tiers should be placed in the ``flask_app`` group vars e.g (flask_app_db_port)
* variables for the ``web`` tier comes into the ``flask_web`` group vars e.g (dns_servers for dmz)
* variables for the ``db`` tier comes into the ``flask_db`` group vars e.g (dns_servers for internal zones)


Mixing multitier and multienv
-----------------------------

* create the inventory host groups for production and testing

.. code-block:: yaml

	# file: production
	[flask_web]
	web1.pascal.lab

	[flask_db]
	db.pascal.lab

	[flask_app:children]
	flask_web
	flask_db

	[production:children]
	flask_app

.. code-block:: yaml

	# file: test
	[flask_web]
	web2.pascal.lab

	[flask_db]
	db.pascal.lab

	[flask_app:children]
	flask_web
	flask_db

	[test:children]
	flask_app


Now we've got these groups for our variables:

* flask_web
* flask_db
* flask_app
* test
* production

* specify variables for different tiers and environments

.. code-block:: bash

	group_vars/
	├── all.yml             <- variables for all hosts
	├── flask_app.yml       <- variables for flask_app hosts -> flask_db & flask_web
	└── flask_web.yml       <- variables only for flask_web hosts
	├── flask_db.yml        <- variables only for flask_db hosts
	├── production.yml      <- variables for production environment
	├── test.yml            <- variables for test environment


* variables for all servers

.. code-block:: yaml

	# file: group_vars/all.yml
	---
	allvar: my first variable for all servers

* variables for the app (web & db)

.. code-block:: yaml

    # file: group_vars/flask_app.yml
    ---
    flask_app_db_port: 3306
    flask_app_db_address: '0.0.0.0'
    flask_app_web_port: 8080

* variables for the tiers

.. code-block:: yaml

    # file: group_vars/flask_db.yml
    ---
    ntp_servers:
      - ntp1.internal.lab
      - ntp2.internal.lab
      - ntp3.internal.lab

    # file: group_vars/flask_web.yml
    ---
    ntp_servers:
      - ntp1.dmz.lab
      - ntp2.dmz.lab
      - ntp3.dmz.lab

* variables for the environments

.. code-block:: yaml

	# file: group_vars/production.yml
	---
	flask_app_db_password: myProdPW
	flask_app_version: v1.0

	# file: group_vars/test.yml
	---
	flask_app_db_password: testPW
	flask_app_version: v1.1


* create a playbook to print out the variables

.. code-block:: yaml

	# file: play-mixed.yml
	---
	- hosts: all
	  gather_facts: false
	  tasks:
	    - debug:
	        msg: 'App_DB_Port={{ flask_app_db_port }} - App_Version={{ flask_app_version }} - DB_PW={{ flask_app_db_password }} - DB_Bind_Address={{ flask_app_db_address | default("not set") }} - Web_Port={{ flask_app_web_port | default("not set") }} - NTP_Servers={{ ntp_servers }}'

* run the playbook for both environments (test and prod)

.. code-block:: bash

	# on prod
	ansible-playbook -i prod play-mixed.yml
	TASK [debug] *******************************************************************
	ok: [web1.test.lab] => {
	    "msg": "App_DB_Port=3306 - App_Version=v1.0 - DB_PW=myProdPW - DB_Bind_Address=0.0.0.0 - Web_Port=8080 - NTP_Servers=[u'ntp1.dmz.lab', u'ntp2.dmz.lab', u'ntp3.dmz.lab']"
	}
	ok: [db.test.lab] => {
	    "msg": "App_DB_Port=3306 - App_Version=v1.0 - DB_PW=myProdPW - DB_Bind_Address=0.0.0.0 - Web_Port=8080 - NTP_Servers=[u'ntp1.internal.lab', u'ntp2.internal.lab', u'ntp3.internal.lab']"
	}

.. code-block:: bash

	# on test
	ansible-playbook -i test play-mixed.yml
	TASK [debug] *******************************************************************
	ok: [web2.test.lab] => {
	    "msg": "App_DB_Port=3306 - App_Version=v1.1 - DB_PW=testPW - DB_Bind_Address=0.0.0.0 - Web_Port=8080 - NTP_Servers=[u'ntp1.dmz.lab', u'ntp2.dmz.lab', u'ntp3.dmz.lab']"
	}
	ok: [db.test.lab] => {
	    "msg": "App_DB_Port=3306 - App_Version=v1.1 - DB_PW=testPW - DB_Bind_Address=0.0.0.0 - Web_Port=8080 - NTP_Servers=[u'ntp1.internal.lab', u'ntp2.internal.lab', u'ntp3.internal.lab']"
	}

.. important::

    This is just a structure example to show how you can define different variable values for tiers and environments. Try to use only a few group_vars files and combine them (like ``flask_app``)


Setup the playbooks
-------------------
* create a playbook for the web tier ``flask_web``

.. code-block:: yaml

    # file: play-flask_web.yml
    ---
    - hosts: flask_web
      roles:
        - web_part

* create a playbook for the db tier ``flask_db``

.. code-block:: yaml

    # file: play-flask_db.yml
    ---
    - hosts: flask_db
      roles:
        - db_part

* create a "master" playbook and import the ``web`` and ``db`` playbooks

.. code-block:: yaml

    # file: site.yml
    ---
    - import_playbooks: play-flask_web.yml
    - import_playbooks: play-flask_db.yml


Links
-----
* https://www.digitalocean.com/community/tutorials/how-to-manage-multistage-environments-with-ansible