Hi,
We’ve run into an issue (and a pattern really) using ansible that we’ve been unable to solve and I’m hoping the list can teach us the “ansible way”.
The background is that we want to create a number of monitors automatically, based on certain information. The solution we have today is a variable:
monitor_exchanges:
- name: exchange1
demand_partners:
- ‘dp1’
- ‘dp2’
And the consumer:
- name: Create datadog monitors
datadog_monitor:
state: “present”
type: “query alert”
name: ‘{{item.0.name}}-{{item.1}} over delivery’
query: “avg({{monitor_interval}}):100*(avg:requests.outbound.transmitted.count{sp_name:{{item.0.name}}, dp_name:{{item.1}}} - avg:demand_partner.rps{sp_name:{{item.0.name}}, dp_name:{{item.1}}})/avg:demand_partner.rps{sp_name:{{item.0.name}}, dp_name:{{item.1}}} > {{monitor_threshold}}”
message: “test”
api_key: “{{datadog_api_key}}”
app_key: “{{datadog_app_key}}”
with_subelements:
- monitor_exchanges
- demand_partners
when: monitor_exchanges is defined
This then creates, for each exchange a monitor per demand partner. That part is fairly easy and works fine but we wanted to externalize the ‘query’/‘name’/‘message’ part of the above thing, so that we’d have something more like:
- name: Create monitors
datadog_monitor:
state: “present”
type: “query alert”
query: {{item.something.query}}
name: {{item.something.query}}
message: {{item.something.query}}
We kept trying to do this with two datastructures, the one from above and then
something like “monitors” that would be a list of hashes containing each monitor to create. I couldn’t come up with the right combination of iteration to make it work however, because I really needed to iterate over two separate things in different ways, I couldn’t just list the two structures, I needed to do something more like:
with_nested:
- with_subelements:
- monitor_exchanges
- demand_partners
- monitors
Is there another way I can model this that makes sense? I really just want to iterate over a list of monitors and then for each monitor iterate over the monitor_exchanges list to pull all the appropriate data.
The fundamental problem is that Ansible doesn’t allow nested loops – even though Ansible looks like a procedural language (it’s executing commands/modules in order and it can loop over things), it really isn’t. The only “simulation” of a for/while loop is the with_foobar stuff, which calls a lookup plugin that must return a simple list to iterate over. You could write your own lookup plugin that does a combination of the subelements and nested plugins, but if you want to stay in the “Ansible realm”, then here’s a solution that I used to solve a similar problem:
Define a helper variable that does the work of with_subelements:
`
monitor_exchange_demand_partners: |
{%- set result = -%}
{%- for exchange in monitor_exchanges|default() -%}
{%- do result.extend(exchange.demand_partners|default() -%}
{%- endfor -%}
{{ result|unique }}
`
That exploits the fact that Ansible variables are Jinja templates, and that if a template evaluates into a string representation of a list or dict it will be converted to that list/dict. You’ll have to add this to your ansible.cfg (Ansible variables in combination with Jinja look like a functional language, but Jinja lacks all the important tools of functional programming, so we’ll use an extension that turns Jinja into a procedural language instead):
`
[defaults]
jinja2_extensions = jinja2.ext.do
`
Then you can use a simple with_nested:
`
- datadog_monitor: …
with_nested:
- monitor_exchange_demand_partners
- monitors
`
this won't work
with_nested:
- with_subelements:
- monitor_exchanges
- demand_partners
- monitors
but this will:
with_nested:
- "{{lookup('subelements', [monitor_exchanges, demand_partners]}""
- monitors
I'm not sure that will get you what you want, but it should correctly
combine the lookups now
Hi Brian,
I am trying to implement your suggestion, I am getting:
“ERROR! an unexpected type error occurred. Error was sequence item 0: expected string, tuple found” (I fixed the obvious typo in your code)
Does this ring a bell?
are you using current devel?
yes, on devel, last synced on Jun 16.
some of the lookups are not working correctly with devel, that woudl
be the error messasge you get