You can pass variables in command line.

ansible-playbook release.yml --extra-vars "version=1.23.45 other_variable=foo"

You can define variables in the playbook. And keep a separate (git ignored) file for some variables.

---
- hosts: all
  remote_user: root
  vars:
    favcolor: blue
  vars_files:
    - /secret_vars.yml
  tasks:
    - name: this is just a placeholder
      command: /bin/echo foo

---
# secret_vars.yml
password: magic
foo:
  field1: one
  field2: two
# dicts can be accessed with foo.field1

You can pass variables to includes and roles.

tasks:
  - include: wordpress.yml wp_user=timmy

roles:
  - { role: foo_app_instance, dir: '/opt/a',  app_port: 5000 }

You can define a variable from task output with register. If a task fails or is skipped, the variable still is registered with a failure or skipped status.

- hosts: web_servers
  tasks:
     - shell: /usr/bin/foo
       register: foo_result
       ignore_errors: True
     - shell: /usr/bin/bar
       when: foo_result.rc == 5

You can define variables with dynamic inventory. These can be group variables or host specific variables.

You can prompt the user for variables.

---
- hosts: all
  remote_user: root
  vars_prompt:
    - name: "name"
      prompt: "what is your name?"
    - name: "secret"
      prompt: "what is your secret?"
      private: yes                      ; won't be shown in output
                                        ; there is also `encrypt` option
    - name: "favcolor"
      prompt: "what is your favorite color?"
      default: "red"

setup module allows assigning "facts" to variables. After running setup: task, the variables are available in the scope of that host.

ansible all -m setup

...
"ansible_lsb": {
  "codename": "xenial",
  "description": "Ubuntu 16.04.1 LTS",
  "id": "Ubuntu",
  "major_release": "16",
  "release": "16.04"
},
...

Sources

• Getting started with ansible in 5 minutes