Create a host inventory in a minute with Ansible

I recently needed to get the overview of an infrastructure: How many servers? Operation systems? Hardware usages (CPU, RAM, disk, …)?

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Unfortunately the company didn’t have any up-to-date host inventory or centralized management. It was necessary to get server information from each hypervisor and complete the list with servers from cloud providers.

Instead of starting a long inventory or monitoring project, I did it with Ansible and the awesome ansible-cmdb module wrote by Ferry Boender.

On the technical part, ansible-cmdb is a smart use of Ansible facts information. It know how to render it in very convenient formats.

The good news is that we don’t need to install any program on servers, everything will be done locally by Ansible and ansible-cmd.

First step is to create an Ansible inventory, this part is quite simple because we just need to write a host listing (one per line). Groups are not necessary for the inventory.

vim hosts
pa2-app01
pa2-app02
pa2-app03
pa2-mysql01
[...]

Ansible setup module is often used to debug because it shows all host information. When fact caching is enabled or using “tree” option in CLI facts are saved on disk.

Execute the following command to collect information about all servers listed in “hosts” file and save it to “out” directory.

ansible -i hosts -m setup --tree out/ all

Directory “out” is now created and contains a file for each server of your inventory.

$ ls out/
pa2-app01 pa2-app02 pa2-app03 pa2-mysql01 pa2-mysql02 pa2-redis01
[...]

Now we need to install ansible-cmdb, we are using python installer. Obviously packages are available for main linux distributions.

pip install ansible-cmdb

Then we use ansible-cmdb to generate inventory by specifying host facts directory:

ansible-cmdb -t html_fancy_split -p local_js=1 out/
open cmdb/index.html

By default all information (server list and all server information) is displayed on the same page, rendering could be a bit slow with lots of servers and columns.

Option “-t html_fancy_split” specifies a built-in template where server information is separated in several files and “-p local_js=1” store javascript in HTML (helpful for offline use).

Inventory main page

It’s also possible to export host inventory to other formats like CSV or SQL.

ansible-cmdb -t csv out > overview.csv

Because ansible-cmd use Ansible facts, it is possible to extend inventory to devices that Ansible can’t fetch like network devices or storage systems by adding facts manually.

mkdir out_manual

We must declare each device with the minimal Ansible host fact structure:

vim out_manual/pa2-fw01
{
  "groups": [
  ],
  "ansible_facts": {
    "ansible_default_ipv4": {
      "address": "172.16.1.1"
    }, 
    "ansible_all_ipv4_addresses": [
      "172.16.1.1",
      "172.16.2.1",
      "172.16.3.1",
      "172.16.4.1"
    ], 
    "ansible_interfaces": [
        "port1", 
        "port2", 
        "port3", 
        "port4"
    ], 
    "ansible_hostname": "pa2-fw01", 
    "ansible_nodename": "pa2-fw01", 
    "ansible_system_vendor": "Fortinet", 
    "ansible_distribution": "Fortigate", 
    "ansible_distribution_version": "100D", 
    "ansible_system": "FortiOS", 
    "ansible_kernel": "5.6.1", 
    "ansible_product_name": "100D", 
    "ansible_product_serial": "FGT-602803031004", 
    "ansible_memtotal_mb": 4096, 
    "ansible_processor_cores": 1
  }, 
  "changed": false
}

Then we regenerate host inventory including manual facts directory:

ansible-cmdb -t html_fancy_split out/ out_manual/
open cmdb/index.html

Pro tips: If you already use Ansible to manage your infrastructure, you could just enable fact caching on Ansible server and execute ansible-cmd in a CRON job to keep your inventory up-to-date :)

More information and references:

• Ansible-cmd Github page
• Ansible setup module