On 1/30/20 5:24 PM, Eric S wrote:
> Racke,
> Thanks for your response.
>
> In practice, what would this look like?
>
> 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.
Regards
Racke
>
> On Wednesday, January 29, 2020 at 10:28:07 PM UTC-8, Stefan Hornburg (Racke)
> wrote:
>
> On 1/30/20 1:48 AM, Eric S wrote:
> > 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.
>
> Regards
> Racke
>
> >
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