Hi Folks,
I am looking for a simple way to have Ansible perform the following automation for me:
From a set of N hosts, find out which host has the lowest CPU usage at the moment
Run a command on only that host.
This pattern could be extended to a general case of:
Run a command on a subset of hosts matching a condition which is not static.
This could apply for the following types of use cases:
Find out which hosts are running low on disk space, and only expand disk space on the hosts which are running low
Find out which hosts are lacking a particular upgrade, and only upgrade those hosts
Only run a command on machines which are not currently under heavy load
This seems like a common and desirable enough pattern, but as far as I can tell there is not a well defined way to execute this with Ansible. Is there a simple way to do this with a playbook, or do I need to write a strategy plugin?
Hi Folks,
I am looking for a simple way to have Ansible perform the following automation for me:
1. From a set of N hosts, find out which host has the lowest CPU usage at the moment
2. Run a command on *only that host*.
This pattern could be extended to a general case of:
Run a command on a subset of hosts matching a condition which is not static.
This could apply for the following types of use cases:
* Find out which hosts are running low on disk space, and only expand disk space on the hosts which are running low
* Find out which hosts are lacking a particular upgrade, and only upgrade those hosts
* Only run a command on machines which are not currently under heavy load
This seems like a common and desirable enough pattern, but as far as I can tell there is not a well defined way to
execute this with Ansible. Is there a simple way to do this with a playbook, or do I need to write a strategy plugin?
Thanks,
Eric
Hello Eric,
you could try to add the hosts to a new group with the "add_host" module and execute the command with delegate_to in
a loop over the hosts in that group.
So far, I have a playbook that I can use to get a list of CPU values. However, I am having trouble correlating the value of CPU to its corresponding hostname.
So far, I have a playbook that I can use to get a list of CPU values. However, I am having trouble correlating the value
of CPU to its corresponding hostname.
---
- hosts: host_list
gather_facts: false
tasks:
- name: Get CPU usage
shell: "top -b -n 1 | head -n3 | tail -n1 | awk '{print $2}'"
register: top
- name: Set CPU fact
set_fact:
cpu_list: "{{ ansible_play_hosts | map('extract', hostvars, 'top') | map(attribute='stdout') | list }}"
Is this on the right track, or do I want a different approach entirely?
Thanks,
Eric
Hello Eric,
this can be done, but I doubt that it makes sense to do it with Ansible as above (especially with a lot of hosts).
Collect system metrics on each server with something like Telegraf and base your decisions on that.