ansible - variable within variable

Question

Ansible 1.9.2 version.

Does Ansible supports variable expansion within a variable while evaluating it.

I have a task to download 3 zip files from Artifactory.

Instead of writing 3 separate tasks within the role, I used ansible's loop in the playbook. In Ansible role's default/main.yml, I have all the required variables defined/available to the role i.e. jmeterplugins_extras_artifactory_url and other (standard / webdriver) are visible to perf_tests role.

---
#- Download and install JMeterPlugins
# Use get_url when Ansible is 2.0+ is available on the machine (otherwise, we can't use get_url) thus, using wget.
- name: Download JMeterPlugins-*
  command: wget {{ jmeterplugins_{{ item.plugin }}_artifactory_url }}  
    chdir="{{ common_download_dir }}"
    creates="{{ common_download_dir }}/{{ jmeterplugins_{{ item.plugin }}_file }}"
  with_items:
    - { plugin: 'extras' }
    - { plugin: 'standard' }  
    - { plugin: 'webdriver' }

But with the above code, I'm getting an error (as shown below):

15:58:57 TASK: [perf_tests | Download JMeterPlugins-*] ********************************* 
15:58:57 <jmeter01.super.fast.jenkins> ESTABLISH CONNECTION FOR USER: cmuser on PORT 22 TO jmeter01.super.fast.jenkins
15:58:57 fatal: [jmeter01.super.fast.jenkins] => Failed to template wget {{ jmeterplugins_{{ item.plugin }}_artifactory_url }} chdir="{{ common_download_dir }}" creates="{{ common_download_dir }}/{{ jmeterplugins_{{ item.plugin }}_file }}": template error while templating string: expected token 'variable_end', got '{'
15:58:57 
15:58:57 FATAL: all hosts have already failed -- aborting
15:58:57 
15:58:57 PLAY RECAP ******************************************************************** 
15:58:57            to retry, use: --limit @/home/cmuser/perf_tests.retry
15:58:57 
15:58:57 jmeter01.super.fast.jenkins : ok=23   changed=6    unreachable=1    failed=0

Doesn't ansible supports variable expansion/evaluation if a variable contains another variable (especially when I'm using a loop).

I just dont want to expand my simple loop task into 3 different -name tasks for downloading zip files for jmeterplugins_extras, jmeterplugins_standard and jmeterplugins_webdriver separately. It seems like the error is related due to Jinja.

How can I use var's value giga in another variable i.e. if var contains giga, then I should get the value of variable "special_giga_variable" ({{special_{{ var }}_variable}})? where var was defined in defaults/main.yml as:

var: giga

karolyi · Accepted Answer · 2017-03-05 23:06:27Z

26

It does.

You can use

set_fact:
  variable: '{{ vars['my_' + variablename + '_variable'] }}'

the only downside of this approach so far is, it won't dynamically expand variables that get the value of another variable. an example:

roles/xxx/defaults/main.yml:

var1: foo
var2: '{{ var1 }}'

This, unfortunately will not work when trying to use the resolved value in var2. Hence,

- debug: msg='{{ vars["var2"] }}'

will output {{ var1 }} instead of foo.

Workaround:

In your vars declaration, instead of using var2: {{ var1 }}, use var2: '{{ vars["var1"] }}'. That way, it will work.

edited Mar 5, 2017 at 23:06

answered Mar 5, 2017 at 20:18

karolyi

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2 Comments

Nathaniel Rogers Over a year ago

Super useful! Looks like there's a global variable called vars. You learn something new everyday.

pedz Over a year ago

It would be nice to see an official Ansible page that documents this. I've yet to find one and would appreciate it if anyone finds the official documentation on this.

palacsint · Accepted Answer · 2016-03-18 00:01:52Z

3

No it doesn't. But it doesn't mean that you have to expand it into 3 different tasks. What you can do is actually expand you "dictionary" to look similar to this:

with_items:
 - {"url": "https://xxxxx", "file": "/tmp/xxxxx" }
 - {"url": "https://yyyyy", "file": "/tmp/yyyyy" }
 - {"url": "https://zzzzz", "file": "/tmp/zzzzz" }

Then in your task just call different parameters: {{ item.url }} and {{ item.file }}

Alternative Options:

Write your own filter that will expand your variable according to the value {{ jmeterplugins_url | my_custom_filter(item.plugin) }}
Write a custom module, that will encapsulate all of the functionality of fetching url into the file based on your inputs
Write custom lookup_plugin that will iterate through your list of variables and produce correct result.
Since you are using command module you can leverage bash to concatenate your url, file in the same command ( this would probably be the messiest solution )

edited Mar 18, 2016 at 0:01

palacsint

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answered Sep 21, 2015 at 21:05

Vor

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3 Comments

AKS Over a year ago

I like that, I did look into those last week thought I should try the simplest approach. The only issue with this is, now I have to define the actual URL and file values in the task itself (and make it more messy) instead of a more cleaner approach. But thanks Vor, I'll try this item.xxx approach. I wonder, if there's any other way to achieve what I actually wanted.

Vor Over a year ago

@ArunSangal I've added few more alternate solutions. They will provide much "cleaner" playbooks but will require little more work to hide all the messy concatenation.

AKS Over a year ago

Sure. I'm looking at those. How's this different: {{ hostvars[inventory_hostname][fact_name] }}. I wonder if this will work: {{ jmeterplugins_[item.plugin]_artifactory_url }} ... i.e. instead of using {{ }} to wrap the variable (which needs to be expanded), if I can use big brackets [ ]

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