The ansible_default_ipv4 magic variable will capture a managed node (e.g. the target system) network interface information, such as the IP address, subnet mask, and default gateway. Or, the following can be used to invoke this module on the control node (that's your Ansible server). 

• local_action module
• delegate_to parameter
• connection parameter
• hostvars magic variable

For example, let's say you have the following playbook. 

---
- hosts: all
  tasks:
    - debug:
        msg: "{{ ansible_default_ipv4 }}"

If you get the following output, the gather_facts module may be set to false. gather_facts must be set to true, or not defined at all in your playbook, as gather_facts is true by default.

TASK [debug]
fatal: [server1.example.com]: FAILED! => {"msg": "The task includes an option with an undefined variable. The error was: 'ansible_default_ipv4' is undefined\n\nThe error appears to be in 'testing.yml': line 8, column 7, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n  tasks:\n    - debug:\n      ^ here\n"}

Running this playbook should return something like this.

TASK [debug]
ok: [server1.example.com] => {
    "msg": {
        "address": "192.168.0.6",
        "alias": "eno16777984",
        "broadcast": "192.168.0.255",
        "gateway": "192.168.0.1",
        "interface": "eno16777984",
        "macaddress": "00:0c:29:fc:f5:79",
        "mtu": 1500,
        "netmask": "255.255.255.0",
        "network": "192.168.0.0",
        "type": "ether"
    }
}

To only capture the IP address, you would append .address, like this.

---
- hosts: all
  tasks:
    - debug:
        msg: "{{ ansible_default_ipv4.address }}"

The following should be returned.

TASK [debug]
ok: [server1.example.com] => {
    "msg": "192.168.0.6"
}