how to use json file consisting of host info as input to ansible inventory

Question

I am trying to use the following json file as input to ansible host inventory but I get error when I run the playbook. JSON File:

{
   "instances":{
       "host": 10.66.70.33
   }
}

Playbook:

hosts: "{{ instances.host }}"
remote_user: root #vars:

When I run the play book I get the following errors. I am not sure where I am doing wrong. I am new to Ansible. Please advice I guess i am doing some silly mistake.

[WARNING]: Could not match supplied host pattern, ignoring: all [WARNING]: provided hosts list is empty, only localhost is available ERROR! The field 'hosts' has an invalid value, which includes an undefined variable. The error was: 'instances' is undefined

I am running the playbook as follows:

ansible-playbook -i <path>/test.json <path>test_playbook.yml

Answer 1

Ansible's yaml plugin will actually parse a JSON file, and has done so for years.

It's barely documented but you can see in the parameters section of the yaml plugin docs, .json is listed as a valid extension.

The JSON format has the same semantics as the YAML format. Note: not the same format as the dynamic inventory!

So your JSON should look like,

{
   "instances": {
      "hosts": {
         "10.66.70.33": null
      }
   }
}

Note: it's "hosts" rather than "host" and each address is a dictionary/hash key with the values being host-specific vars.

Taking the first example from Working with Inventory docs,

all:
  hosts:
    mail.example.com:
  children:
    webservers:
      hosts:
        foo.example.com:
        bar.example.com:
    dbservers:
      hosts:
        one.example.com:
        two.example.com:
        three.example.com:

would look like,

{
  "all": {
    "hosts": {
      "mail.example.com": null
    },
    "children": {
      "webservers": {
        "hosts": {
          "foo.example.com": null,
          "bar.example.com": null
        }
      },
      "dbservers": {
        "hosts": {
          "one.example.com": null,
          "two.example.com": null,
          "three.example.com": null
        }
      }
    }
  }
}

Those nulls are odd-looking but in the YAML example you'll see the trailing colon which does indeed mean each of those hosts are effectively dictionary/hash keys.

For the curious, the JSON-then-YAML loading code is in parsing/utils/yaml.py and the actual parsing is in parsing/inventory/yaml.py.

Answer 2

It seems pure JSON it's not supported as inventory file. In the inventory plugin list I don't see JSON:

• advanced_host_list - Parses a ‘host list’ with ranges
• auto - Loads and executes an inventory plugin specified in a YAML config
• aws_ec2 - ec2 inventory source
• constructed - Uses Jinja2 to construct vars and groups based on existing inventory.
• host_list - Parses a ‘host list’ string
• ini - Uses an Ansible INI file as inventory source.
• k8s - Kubernetes (K8s) inventory source
• openshift - OpenShift inventory source
• openstack - OpenStack inventory source
• script - Executes an inventory script that returns JSON
• virtualbox - virtualbox inventory source
• yaml - Uses a specifically YAML file as inventory source.

On the other hand you can wrap that JSON in a simple python script as follows:

1. Make sure the script plugin is enabled in your ansible.cfg file:

   [inventory]
   enable_plugins = host_list, script, yaml, ini
   

2. Create wrapper script (inventory file), only reads your JSON and prints it in the console (I'm assuming the JSON and the wrapper script are in the same path):

   #!/usr/bin/env python
   import os
   
   __location__ = os.path.realpath(
       os.path.join(os.getcwd(), os.path.dirname(__file__)))
   
   with open(os.path.join(__location__, "hosts.json")) as f:
       print f.read()
   

3. Use the following in your JSON inventory (performance improvements):

   {
       "_meta": {
           "hostvars": { }
       },
   
       "instances": {
           "hosts": ["10.66.70.33"]
       }
   }
   

4. When running the playbook just be aware the group you want to target should be "instances", for example this is my playbook:

   ---
   - hosts: instances
     tasks:
       - debug:
           msg: Hi there
   

Then just run the playbook as you did, specifying the python wrapper script, in my case this was:

ansible-playbook -i inventory/hostswrapper.py test-stkovfl.yml

Hope it helps!