The b64encode filter is used to encode a string. The b64decode filter is used to decode a string. In this example, string foo is encoded.

Notice in this example that foo is wrapped in quotes. When wrapped in quotes, foo is interpreted as a string. If foo were not wrapped in quotes, foo would be interpreted as a variable.

- name: "encoded the 'foo' string"
  debug:
    msg: "{{ 'foo' | b64encode }}"

The following should be returned.

TASK [encode the 'foo' string]
ok: [server1.example.com] => {
    "msg": [
        "Zm9v"
    ]
}

Let's say you are using the vars plugin to create a variable. In this example, the foo variable contains a value of Hello.

vars:
  foo: "Hello"

Here is how you would encode the foo variable, which will encode value Hello. Notice that foo is not wrapped in quotes, so that foo is interpreted as a variable, not a string.

- name: "encoded the 'foo' variable"
  debug:
    msg: "{{ foo | b64encode }}"

The following should be returned.

TASK [encode the 'foo' variable]
ok: [server1.example.com] => {
    "msg": [
        ""SGVsbG8="
    ]
}