Reload Ansible's dynamic inventory

48
votes

I'm using Ansible to setup EC2 instances and deploy an app. There's a hosts script which gathers tags related servers and groups info. I'd like to run these actions as a single playbook, so

  1. New instances are created if needed
  2. Hosts script loads inventory (including servers' facts)
  3. Deployment playbook works

However, inventory loaded in advance so there is no servers/groups data if servers created/updated during the play. I can 1) separate provision and deployment playbooks 2) use add_host trick to emulate dynamic inventory when servers are updated, but there are drawbacks in those approaches.

Can I force Ansible to reload inventory? My test files are: hosts script:

#!/bin/sh
echo `date` >> log.log
echo "{\"standalone\":[\"localhost\"]}"

Sample playbook.yml:

---
- hosts: all
  tasks:
    - name: show inventory_hostname
      command: echo {{ inventory_hostname }}

I run it ansible-playbook -i hosts playbook.yml -v and see two runs:

$> cat log.log
Thu Mar 12 09:43:16 SAMT 2015
Thu Mar 12 09:43:16 SAMT 2015

but I haven't found a command to double it.

7
ansibleansible-inventory
What drawback do you see with add_host module? – Mxx
@Mxx It's a logic duplication, isn't it? I don't want to think about cases when all servers brand new, or when they are changed partly (my distribution model includes several servers). Moreover, hosts script generate some local facts, should I copy it as well? – Vladimir Chervanev
I agree with Vladimir @Mxx. Using add_host here is duplicative. I am provisioning a number of hosts based on a list, but this breaks the "register: ec2" pattern that's common in ansible ec2 provisioning examples, because the result is a list of return values. Ideally ansible would allow me to run a two-phased provisioning process in the same playbook: 1) create a bunch of instances, then 2) address them by group and do some basic configuration (like setting up DNS, etc). – brentiumbrent
Can confirm: add_host is suboptimal to say the least. – J0hnG4lt

7 Answers

49
votes

With Ansible 2.0+, you can refresh your inventory mid-play by running the task:

- meta: refresh_inventory
21
votes

I found the meta: refresh_inventory to be insufficient.
I had to add an explicit call to ec2.py --refresh-cache first.

- name: refresh inventory
  hosts: localhost
  connection: local
  gather_facts: False
  tasks:
    - name: Refresh EC2 cache
      command: /etc/ansible/ec2.py --refresh-cache
    - name: Refresh in-memory EC2 cache
      meta: refresh_inventory
6
votes

Ansible currently doesn't support this. If you look at the source code of the ansible or ansible-playbook commands you'll see that the inventory is loaded first and then the inventory object is passed to the ansible command that runs the specified task or playbook. Moving the inventory processing so that it happens within the task/playbook handlers would probably be a pretty major undertaking for a number of reasons.

Your best bet when doing something like this is to simply break your playbook into two and wrap their calls in a shell script that you only have to invoke once.

2
votes

You can also edit the ec2.ini file and set the option:

cache_max_age = 0

to prevent the need for reload by making sure that nothing is cached in the first place.

0
votes

I had a similar scenario and meta did not help, but setup did. So, this is for all folks that might find this useful... To give a little bit of context, what I was doing is to limit the linux kernel memory to a certain amount of what the real memory was and then update some files based on the new values.

For instance, the ansible tasks were something like:

- name: Print real memory
  debug:
    msg: {{ ansible_memory_mb.real.total }}

- name: Reset GRUB_CMDLINE_LINUX
  lineinfile:
    path: /etc/default/grub
    regexp: '^{{ item.key }}='
    line: '{{ item.key }}="{{ item.value }}"'
  with_items:
    - { key: 'GRUB_CMDLINE_LINUX', 
        value: '{{ ansible_memory_mb.real.total - reserved }}m'}

- name: Update GRUB
  command: update-grub

- name: Reboot the node to load the system's real memory settings
  reboot:

- name: Print real memory
  debug:
    msg: {{ ansible_memory_mb.real.total }}

and the output was the same for both debug logs because the ansible_memory_mb variable was not reload after the linux kernel configuration changed.

Solution? Add a task to setup after rebooting the system.

- name: Refresh ansible facts (ansible_memory_mb) after updating grub
  setup:
0
votes

Please note that meta: refresh_inventory does not work in Ansible Tower (AWX).

https://docs.ansible.com/ansible-tower/3.3.1/html/userguide/best_practices.html

Playbooks should not use the meta: refresh_inventory Ansible feature, as it is incompatible with how Tower processes inventory, if a playbook does refresh inventory, it will refresh back to the start of the inventory the job began with. Instead, use a workflow with separate inventory refresh steps.

I do not yet have enough rep to comment, otherwise, I would have.

-2
votes

Take a look at add_host.

It does add a host (and alternatively a group) to the ansible-playbook in-memory inventory