Environment:
https://github.com/ansible/ansible-examples/blob/master/language_features/environment.yml

- hosts: all
  remote_user: root
  # here we make a variable named "env" that is a dictionary
  vars:
    env: 
       HI: test2
       http_proxy: http://proxy.example.com:8080
  tasks:
    # here we just define the dictionary directly and use it
    # (here $HI is the shell variable as nothing in Ansible will replace it)
    - shell: echo $HI
      environment:
         HI: test1
    # here we are using the $env variable above
    - shell: echo $HI
      environment: env


Conditionals:

http://docs.ansible.com/ansible/playbooks_conditionals.html

Sometimes you will want to do certain things differently in a playbook based on certain criteria.
Having one playbook that works on multiple platforms and OS versions is a good example.

As an example, the name of the Apache package may be different between CentOS and Debian,
but it is easily handled with a minimum of syntax in an Ansible Playbook:

---
- hosts: all
  remote_user: root
  vars_files:
    - "vars/common.yml"
    - [ "vars/{{ ansible_os_family }}.yml", "vars/os_defaults.yml" ]
  tasks:
  - name: make sure apache is running
    service: name={{ apache }} state=running

As a reminder, the various YAML files contain just keys and values:

---
# for vars/CentOS.yml
apache: httpd
somethingelse: 42

How does this work?
If the operating system was ‘CentOS’, the first file Ansible would try to import would be ‘vars/CentOS.yml’,
followed by ‘/vars/os_defaults.yml’ if that file did not exist.
If no files in the list were found, an error would be raised.
On Debian, it would instead first look towards ‘vars/Debian.yml’ instead of ‘vars/CentOS.yml’,
before falling back on ‘vars/os_defaults.yml’.
Pretty simple.

To use this conditional import feature, you’ll need facter or ohai installed prior to running the playbook,
but you can of course push this out with Ansible if you like:

# for facter
ansible -m yum -a "pkg=facter state=present"
ansible -m yum -a "pkg=ruby-json state=present"

# for ohai
ansible -m yum -a "pkg=ohai state=present"

Ansible’s approach to configuration – separating variables from tasks, keeps your playbooks from turning into arbitrary code
with ugly nested ifs, conditionals, and so on - and results in more streamlined & auditable configuration rules –
especially because there are a minimum of decision points to track.




Sometimes a configuration file you want to copy, or a template you will use may depend on a variable.
The following construct selects the first available file appropriate for the variables of a given host,
which is often much cleaner than putting a lot of if conditionals in a template.

The following example shows how to template out a configuration file that was very different between, say, CentOS and Debian:

- name: template a file
  template: src={{ item }} dest=/etc/myapp/foo.conf
  with_first_found:
    - files:
       - {{ ansible_distribution }}.conf
       - default.conf
      paths:
       - search_location_one/somedir/
       - /opt/other_location/somedir/