Thanks for the help, Josh.
I actually am trying to run a command once on a certain set of EC2
instances I'm managing that match a specific tag. This seems like a very
reasonable thing to do and yet the run_once skipping functionality makes
this quite difficult. I managed to find two similar but different ways to
do this (though not exactly elegant), which I'll post for future reference.
I was inspired by
https://groups.google.com/forum/#!topic/ansible-project/cpnrBRxLy0E and
https://imil.net/blog/2016/08/05/Ansible_and_AWS_ASG
*Method 1* (serial 1 is important due to the add_host behavior Josh pointed
out). Run the playbook with the AWS dynamic inventory script (-i ec2.py)
- hosts: ec2
user: ubuntu
serial: 1
gather_facts: false
tasks:
- name: add only nodes that don't match your_tag_name to in-memory host
group
add_host:
name: "{{ inventory_hostname }}"
groups: your_hosts
when: ec2_tag_Name != your_tag_name
and then run the rest of your playbook not serially and perform run_once
actions like this:
- hosts: ec2
user: ubuntu
gather_facts: true
tasks:
- name: Run once on your_tag_name
shell: echo yes >> yes.txt
run_once: true
delegate_to: "{{ groups['your_hosts'][0] }}"
*Method 2: *use the ec2_instance_facts module to create the in-memory
group. This requires a tag name variable or constant you can reference to
match instances with
- hosts: localhost
user: ubuntu
connection: local
gather_facts: true
tasks:
- name: create an in memory group of only nodes with your_tag_name
add_host:
name: "{{ item }}"
groups: your_hosts
with_items: "{{ ec2.instances | selectattr('state.name', 'equalto',
'running') | selectattr('tags.Name', 'equalto', your_tag_name ) |
map(attribute='public_ip_address')|list }}"
Either way, if you want to use the information from ec2.py then you'll end
up having two hosts sections and some verbosity. I suppose with the
ec2_instance_facts one could potentially create groups of EC2 hosts and run
the playbook all with hosts: localhost and delegate tasks to certain
groups? I haven't tried this as I've spend enough time getting run_once to
work for now.
Dave
On Friday, December 8, 2017 at 1:14:17 PM UTC-7, Josh Smift wrote:
>
> > Weirdly, when I try to create an in-memory host group using when and
> > add_host the task only gets executed one time (on a skipped host). I
> > don't have run_once on this task so I'm not sure why all my nodes aren't
> > executing it. Any ideas?
>
> add_host is implicitly run_once; there's a note about it at the bottom of
> http://docs.ansible.com/ansible/latest/add_host_module.html saying "This
> module bypasses the play host loop and only runs once for all the hosts in
> the play, if you need it to iterate use a with_ directive." Something like
>
> - add_host:
> groups: cool_new_group
> name: "{{ item }}"
> changed_when: False
> with_items: "{{ play_hosts }}"
>
> might do what you need, depending what you need. :^)
>
> -Josh (j...@care.com <javascript:>)
>
> (apologies for the automatic corporate disclaimer that follows)
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