int is a Jinja2 filter, commonly used to:

• Convert a string, boolean, unicode, or AnsibleVaultEncryptedUnicode object into an integer
• Perform a math function (addition, subtraction, multiplication, division)

Convert a string into an integer

For example, lets say you use the vars to create a variable named foo. Notice in this example the double quotes are used, which you would think would set the variable to be a string. The debug module and type_debug filter can be used to show that foo is actually AnsibleUnicode.

---
- hosts: localhost
  vars:
    foo: "10"
  tasks:
  - debug:
      msg: "The 'foo' variable is {{ foo | type_debug }}"
...

Something like this should be returned.

TASK [debug]
ok: [server1.example.com] => {
    "msg": "The 'foo' variable is AnsibleUnicode"
}

AVOID TROUBLE

Jinja2 templating will always return a string

Let's say you then try to use the set_fact module and the int filter to convert foo into an integer.

---
- hosts: localhost
  vars:
    foo: "10"
  tasks:
  - set_fact:
      foo: "{{ foo | int }}"

  - debug:
      msg: "The 'foo' variable is {{ foo | type_debug }}"
...

Something like this should be returned. Now the type is unicode.

TASK [debug]
ok: [server1.example.com] => {
    "msg": "The 'foo' variable is unicode"
}

The underlying issue is that when templating (the Jinja2 curly braces) always returns a string. However, you can still use the int filter in a when statement, since when statements do not use templating, to convert a variable into an int.

---
- hosts: localhost
  vars:
    foo: "10"
  tasks:
  - debug:
      msg: The 'foo' variable contains a value of 10
    when:
      - foo | int == 10
...

Perform a math function

For example, the int filter could use + for addition, like this.

- name: 10 plus 1
  debug: 
    msg: "{{ 10 | int + 1 }}"

Which should return 11.

TASK [10 plus 1]
ok: [server1.example.com] => {
    "msg": [
        "11"
    ]
}

Or using - for subtraction.

- name: 10 minus 1
  debug: 
    msg: "{{ 10 | int - 1 }}"

Or using * for multiplication.

- name: multiply 2 by 3
  debug: 
    msg: "{{ 2 | int * 3 }}"

Or using / for division.

- name: 10 divided by 2
  debug: 
    msg: "{{ 10 | int / 2 }}"

Let's say you are using the vars plugin to create a variable. Notice in this example that the value is not wrapped in quotes. If the value were wrapped in quotes, the value would be interpreted as a string, not an integer.

vars:
  default_value: 100

The debug module can be used to output the value, like this.

- name: output the content of the 'default_value' variable
  debug: 
    msg: "{{ default_value }}"

Which should return the following.

TASK [output the content of the 'default_value' variable]
ok: [server1.example.com] => {
    "msg": [
        "100"
    ]
}

The int filter could be used to increment the value by 1, like this.

- name: increment 'default_value' by 1
  debug: 
    msg: "{{ default_value | int + 1 }}"

Which should return the following.

TASK [increment 'default_value' by 1]
ok: [server1.example.com] => {
    "msg": [
        "101"
    ]
}