Working With JSON in Ansible

17/03/2019

ansible   json

Reading JSON in Ansible is easy. Here are some examples…

This is a JSON array of objects (hosts). Each host has a nested object called customProperties. Assume this is stored in a file called customProperties.json in the same directory as your playbook.

[{
  "hostname": "host1",
  "customProperties": {
    "foo": "first",
    "foo2": "second"
  }
}, {
   "hostname": "host2",
   "customProperties": {
     "foo": "third",
     "foo2": "fourth"
  }
}]

Read JSON Into Ansible

Let’s read this file into Ansible. Once done, it will be available as an Ansible variable called hostList (or whatever you define on line 6 of the playbook).

---
- name: Write vars
  hosts: local

  vars:
    hostList: "{{ lookup('file', 'customProperties.json') }}"

Output Raw JSON

Now extend the playbook to output the RAW JSON object. For this we’ll use the debug module to print out to the screen.

---
- name: Write vars
  hosts: local

  vars:
    hostList: "{{ lookup('file', 'customProperties.json') }}"

  tasks:

  - name: "Output all hostList as-is"
    debug:
      msg: "{{ hostList }}"

Print All Host Names

Using the Ansible loops keyword, we can iterate through each top level object (host) and print out any property, one at a time.

Let’s extend the playbook to loop through and print each hostname value.

Notice the use of the item keyword. This is a special Ansible keyword which refers to the current item in the loop.

---
- name: Write vars
  hosts: local

  vars:
    hostList: "{{ lookup('file', 'customProperties.json') }}"

  tasks:

  - name: "Output all hostList as-is"
    debug:
      msg: "{{ hostList }}"

  - name: "Print all hostnames"
    debug:
      msg: "{{ item.hostname }}"
    loop: "{{ hostList }}"

Print Nested Value

Now for something more complex. Let’s track down deeper into the JSON object to print the value of foo2 for each host.

---
- name: Write vars
  hosts: local

  vars:
    hostList: "{{ lookup('file', 'customProperties.json') }}"

  tasks:

  - name: "Output all hostList as-is"
    debug:
      msg: "{{ hostList }}"

  - name: "Print all hostnames"
    debug:
      msg: "{{ item.hostname }}"
    loop: "{{ hostList }}"

  - name: "Print 'foo2' for each host. Should be 'second' and 'fourth'."
    debug:
      msg: "{{ item.customProperties.foo2 }}"
    loop: "{{ hostList }}"

Print Nested Value When Condition Is Met

Finally, let’s choose to only print the foo value when the hostname is host2.

---
- name: Write vars
  hosts: local

  vars:
    hostList: "{{ lookup('file', 'customProperties.json') }}"

  tasks:

  - name: "Output all customProperties as-is"
    debug:
      msg: "{{ hostList }}"

  - name: "Print all hostnames"
    debug:
      msg: "{{ item.hostname }}"
    loop: "{{ hostList }}"
    
  - name: "Print 'foo2' for each host. Should be 'second' and 'fourth'."
    debug:
      msg: "{{ item.customProperties.foo2 }}"
    loop: "{{ hostList }}"

  - name: "Print 'foo' for host2. Should be 'third'."
    debug:
      msg: "{{ item.customProperties.foo }}"
    loop: "{{ hostList }}"
    when: "item.hostname == 'host2'"

The latest version of the playbook and JSON will always be available on Github.

ansible   json