---
author: Chris Meyers
date: 2018-09-22 00:00 UTC
description: Smart Inventory allows you to generate a new Inventory that
  is made of up hosts existing in other Inventory in Ansible Tower. A
  limitation of the Smart Inventory filter is that it only allows
  equality matching on ansible_fact JSON data. Chris Meyers walks you
  through overcoming this limitation.
lang: en-us
title: Ansible Tower Advanced Smart Inventory Usage
---

# Ansible Tower Advanced Smart Inventory Usage

## Background

[Smart Inventory](http://docs.ansible.com/ansible-tower/latest/html/userguide/inventories.html#smart-inventories)
is a feature that was added to Red Hat Ansible Tower 3.2. The feature
allows you to generate a new Inventory that is made of up hosts existing
in other Inventory in Ansible Tower. This inventory is always-up-to-date
and is populated using what we call a host filter. The host filter is a
domain specific query language that is a mix of Django Rest Framework
GET query language with a JSON query syntax added in. Effectively, this
allows you create an Inventory of Hosts and their relational fields as
well as related JSON structures.

The ansible_facts field is a related field on a Host that is populated
by Job Template runs (Jobs) that have fact caching enabled. Ansible
Tower bolts on an Ansible fact cache plugin with Job Template that have
fact caching enabled. Job Templates of this kind that run playbooks that
invoke Ansible gather_facts will result in those facts being saved to
the Ansible Tower database when the Job finishes.

A limitation of the Smart Inventory filter is that it only allows
equality matching on ansible_fact JSON data. In this blog post I will
show you how to overcome this limitation and add hosts to a Smart
Inventory using, for example, a range query on if a host is part of a
subnet.

### Ansible Tower Objects

Enough talking about it, let's see an example. We are going to have to
create objects in Ansible Tower. Specifically, the objects in the table
below.

| Resource         | Value                                                       |
| ---------------- | ----------------------------------------------------------- |
| Organization     | Transformers                                                |
| Inventory        | Autobots                                                    |
| Project          | [Facts](https://github.com/chrismeyersfsu/ansible-examples) |
| Hosts            | optimus, bumblebee, jazz                                    |
| Job Templates    | [gather](https://github.com/chrismeyersfsu/ansible-examples/blob/master/gather_facts/main.yml), [clear](https://github.com/chrismeyersfsu/ansible-examples/blob/master/clear_facts/main.yml), [subnet](https://github.com/chrismeyersfsu/ansible-examples/blob/master/subnet/main.yml), [set_fact_cacheable](https://github.com/chrismeyersfsu/ansible-examples/blob/master/set_fact/cacheable.yml) |

> Enable fact cache for all the job templates

### 1. Fact Cache

Now, let's make something happen. Run the gather job template. Then look
at the resulting facts that got gathered in the UI for the Inventory
Autobots.

![Tower-Facts-2-Screen](/images/posts/archive/Tower-Facts-2-Screen.png)

Above is an example of how you view the results from the fact gathering
process in the UI. Now let's see how we can create a Smart Inventory
from the facts gathered.

### 2. Our First Smart Inventory

We will create a smart inventory that contains only Red Hat hosts. In my
example, optimus and bumblebee are both Red Hat hosts while jazz is an
Ubuntu host.

![Tower-Smart-Iventory-Screen](/images/posts/archive/Tower-Smart-Iventory-Screen.png)

Create a smart inventory with host filter: `ansible_facts.ansible_distribution:RedHat`

My new smart inventory, Red Hat Autobots, contains 2 hosts (see below image).

![Tower-Inventories-Screen](/images/posts/archive/Tower-Inventories-Screen.png)

### 3. Inject playbook facts

We are now going to leave the Smart Inventory feature and go back to
fact caching. Specifically, I am going to show you how to `set_fact` in
a playbook and have that fact stored in Ansible Tower.

Run the job template `set_fact_cacheable`. Below is the result of that run.

![Tower-Jobs-Screen](/images/posts/archive/Tower-Jobs-Screen.png)

Now, let's look at the facts for any of the 3 hosts that this playbook
ran against. Notice how bumblebee now has a new set of facts (see below
image).

![Tower-Facts-Screen](/images/posts/archive/Tower-Facts-Screen.png)

Specifically:

```yaml
a:
   b:
      c:
        - a
        - b
```

These facts were set by this playbook which uses the set_fact Ansible
module with `cacheable: true` set.

### Create a Smart Inventory

I've showed you all the pieces you are going to need to create a Smart
Inventory based on host facts that aren't simple equality matching. The
pieces are:

1.  Fact Cache
2.  Smart Inventory
3.  Inject playbook facts

Now I'll show you an example using all these pieces to construct a
Smart Inventory of hosts within a subnet. This is a good example because
selecting hosts based on subnet is a range query, it is not a simple
equality query. Therefore, we are going to need to leverage 3. Inject
playbook facts to accomplish creating a Smart Inventory to group these
hosts.

The overall goal is to set `is_subnet` on a host to True if the host is
in the desired subnet, or False if the host is not in the subnet. Then,
we can construct a Smart Inventory host filter like
`ansible_facts.is_subnet:true` to get hosts in the subnet. The below
playbook [accomplishes this](https://github.com/chrismeyersfsu/ansible-examples/blob/master/subnet/main.yml).

```yml
- hosts: all
  vars:
    subnet: '172.18.0.0/16'
  tasks:
    - name: "Presume host to not belong to subnet"
      set_fact:
        is_subnet: False
        cacheable: True

    - name: "Figure out if host belongs to subnet"
      set_fact:
        is_subnet: True
        cacheable: True
      when: ansible_all_ipv4_addresses | ipaddr(subnet)
```

### Future

Currently, all traditional relational database fields on Ansible Tower
objects can be used in a Smart Inventory host filter query (i.e. Host
name, Inventory name, Organization description, etc); the only JSON
searchable field related to Hosts is the ansible_facts field. We hope to
expand the searchable JSON fields in the future as well as the operators
supported (right now we only support equality). However, much
consideration must be given to the performance characteristics as well
as the storage requirements in doing so.