Calculating with Variables?

[Ulrich Hochholdinger]

Hi,
I just started playing around with ansible and tried to achieve a simple operations task with it:

Iterate over all nodes of my Xen-Cluster -- get free_memory of every node and sum up those values.
next step would be making a decision e.g. spawning a new VM without overprovisioning the cluster.

So I wrote a simple module which collects "xm info" values as ansible_facts. This was easy...

Next step: write a playbook which sums up one of the collected fact (free_memory) -- here I got stuck and have no more ideas how to solve this...

This is a not working idea:

# vim:ft=ansible:
---
- hosts: Cluster
  vars:
 # should be initially set to zero??
    sum_free_memory: "{{ sum_free_memory|int + xm_infos.free_memory|int }}"
  tasks:
    - name: gather xen facts
      xm_info:

    - name: show free_memory on host
      debug: msg="{{ xm_infos.free_memory|int }}"

    - name: increment sum_free_memory
      debug: msg="{{ sum_free_memory|int }}"

=> which obviously doesn't work:
ERROR: recursive loop detected in template string: {{ sum_free_memory|int + xm_infos.free_memory|int }}

So how can I sum up collected facts from more than one host?

Cheers
      Ulli

[Tom Bamford]

Hi Ulrich

How about a ‘for’ loop (in Jinja2) contained as a parameter to the set_fact module, iterating the facts you gathered as presented in the {{ hostvars }} magic variable?

Regards
Tom

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[Michael DeHaan]

for loops in Jinja2 can't be used (with any definition of sanity) in Ansible playbooks.

They can be used in templates used by the template module.

Let's step back a moment...

Can you remove the recursive reference and just call it "actual_free_mem" or something, and see where you are from there.

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[Ulrich Hochholdinger]

Hi,
Many thanks for these ideas, since this posting was held back for moderation (it was my first one in this group) I asked the question on irc channel and got the tip: simply write a filter to collect the necessary data to a list which can be summed up."ktosiek" from irc channel wrote me the start of a filter which I modified to solve my problem :D

this is the Filter:

def multiget(dictionary, keys):
    return [int(dictionary[k]['xm_infos']['free_memory']) for k in keys]

which can then be used in a playbook like this:
    - name: show the sum
      debug: msg="{{ hostvars | multiget(keys=groups.Cluster)|sum }}"

The first Idea was to have the filter more generally to use it like this:
debug: msg="{{ hostvars | multiget(keys=groups.Cluster)|sum(attribute=xm_infos.free_memory) }}"
But the values inside the list must be casted to int and I had no other Idea than to do this inside the generation of the list.

 
Cheers
     Ulli

PS: I like ansible more and more especially the really cool and helpfull community ;-D