EC2: collect list of private-ip from on group, use it in a second group

[Tzach Livyatan]

Posted a similar question a few days ago, got the right answer.

Now I can better explain what I'm looking for.

I'm building a EC2 system from two types of servers:

- cluster nodes

- loader nodes

Each loader is generating traffic to ALL cluster nodes.

My goal is a playbook which collect private-ip from each the first group, and use it as part of a command to be executed on the second group.

I assume it should look something like:

---

- name: Collect private IPs

 hosts: tag_Name_ClusterNodes

 gather_facts: false

 tasks:

     - name: Create group

#      Pseudo Code Warning:

      all_cluster_ips += {{ ec2_private_ip_address }}}

- name: Run stress

 hosts: tag_Name_Cloader

 user: ec2-user

  tasks:

   - command: benchmark  {{ all_cluster_ips }}

But I cant make this works.

Suggestions will be appreciated!

Thanks

[James Martin]

Here's a quick sample playbook that should do what you are trying to do.  Keep in mind that the ec2.py dynamic inventory script will gather the private IPs for you, you shouldn't need an explicit task.  

- hosts: localhost
  tasks:

  - debug: msg="{{ hostvars[item].ec2_private_ip_address }}"
    with_items: groups.tag_Name_ClusterNodes
    register: output

  - debug: msg="{{ output.results|map(attribute='msg')|join(' ') }}"

You could also write a custom jinja2 filter to make this a single task.

- James

[Tzach Livyatan]

Thanks James

Works like a charm. register is what I was looking for.

What should I use in production instead of the first debug?

I need the data, not the output to the screen.

[James Martin]

Sorry, I'm not sure of a way to suppress that, outside of using a custom filter.

- James 

[Brian Coca]

look at set_fact

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--
Brian Coca

[James Martin]

Sorry, was a bit confused by your comment "What should I use in production instead of the first debug?"

If you mean, not to use "debug" in your first task because it's too verbose, you don't have to.  But using it is not going to harm anything even on production.  If you want to do it in a less verbose way:

- hosts: localhost
  tasks:
  - command: echo "{{ hostvars[item].ec2_private_ip_address }}"
    with_items: groups.tag_Name_ClusterNodes
    register: output
    changed_when: no

  - debug: msg="{{ output.results|map(attribute='stdout')| join(' ') }}"

as far as the second debug goes, you could, as bcoca pointed out, use set_fact:

- set_fact: ip_list=""{{ output.results|map(attribute='stdout')| join(' ') }}"

And subsequent tasks could then reference the list as "{{ ip_list }}"

- James

[Tzach Livyatan]

Thanks James, Brain

This is precisely what I was looking for!