Multiple Environments
"""""""""""""""""""""

Multiple Environments e.g ``test`` & ``prod``

Using separate inventories
--------------------------
* use different inventory files/folders for your environments!
* you can specify the path to a inventory file with the option ``-i`` for ``ansible`` and ``ansible-playbook``
* to create a multistage inventory, you've to work with ``children``
* create a parent group for your environment and add all other host groups, so you can define variables for the whole environment (for example: use different sshd settings for ``test`` and ``prod``)

.. code-block:: yaml

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

    [db]
    db.pascal.lab

    [production:children]
    web
    db

.. code-block:: yaml

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

    [db]
    db2.pascal.lab

    [test:children]
    web
    db

Now we've got these groups:

* web
* db
* production
* test

.. code-block:: bash

    # list all hosts of a inventory
    ansible -i test all --list-hosts

I can use the defined host groups with ``ansible`` or ``ansible-playbook`` in combination with the separted inventory files.

.. code-block:: bash

    # run ping on the inventory production
    ansible -i production -m ping all

    db.pascal.lab | SUCCESS => {
        "changed": false,
        "ping": "pong"
    }
    web1.pascal.lab | SUCCESS => {
        "changed": false,
        "ping": "pong"
    }


.. hint:: 

    The defined groups are now important for setting different variable values per environment.

.. hint::

    Set the ``test`` inventory as your default inventory in ``ansible.cfg`` => ``inventory = test``. So it's only needed to use ``-i`` for your ``prod`` environment.

Settings variables for environments
-----------------------------------
* define environment variables in your created parent group ``production`` and ``test``
* define variables that can be used on ``all`` hosts
* define variables for ``db`` or ``web``

.. code-block:: yaml

    # file: group_vars/all.yml   <- value for all servers
    db_host: db.pascal.lab

.. code-block:: yaml

    # file: group_vars/production.yml   <- only on production
    db_password: myProdPW
    prod_var: 'this is a production env variable'

.. code-block:: yaml

    # file: group_vars/test.yml   <- only on test
    test_var: 'this is a test env variable'
    db_password: testPW

.. code-block:: yaml

    # file: group_vars/db.yml     <- equal for test & prod, but only for db
    db_setting: limit5

.. code-block:: yaml

    # file: group_vars/web.yml    <- equal for test & prod, but only for web
    web_port: 8080

* tree structure

.. code-block:: bash

    ├── group_vars
    │   ├── all.yml
    │   ├── db.yml
    │   ├── production.yml
    │   ├── test.yml
    │   └── web.yml
    ├── production
    ├── test

.. hint::

    Ansible will search for the ``group_vars`` and ``host_vars`` in the same directory like the inventory file.

.. important::

    There are many ways to define the directory structure.

Check out the variables:

.. code-block:: bash

    # get the prod variables
    ansible -m debug -a "msg={{ prod_var }}" -i production all

    # will fail
    ansible -m debug -a "msg={{ test_var }}" -i production all

    # will fail on the db host
    ansible -m debug -a "msg={{ web_port }}" -i test all

.. hint::

    The structure depends on the amount of servers and needed groups. Sometimes it's better to use a dynamic invetory for create the whole structure for the groups.


Define a new playbook
---------------------

.. code-block:: bash

    # plays/debug.yml
    ---
    - hosts: all

      tasks:
      - name: debug some variables
        debug:
          msg: '{{ prod_var }}'


    ansible-playbook playbooks/debug.yml -i test
    ansible-playbook playbooks/debug.yml -i production


Links
-----
* http://toja.io/using-host-and-group-vars-files-in-ansible/
* http://rosstuck.com/multistage-environments-with-ansible/
* https://github.com/confirm/ansible-git-inventory
* http://docs.ansible.com/ansible/playbooks_best_practices.html#directory-layout
* http://docs.ansible.com/ansible/playbooks_best_practices.html#alternative-directory-layout
* http://docs.ansible.com/ansible/latest/playbooks_best_practices.html#staging-vs-production
* http://docs.ansible.com/ansible/latest/playbooks_best_practices.html#how-to-differentiate-staging-vs-production
* https://www.digitalocean.com/community/tutorials/how-to-manage-multistage-environments-with-ansible