concatenate a value with another variable in default filter

[Nicolas G]

I have the bellow Ansible inventory :

[web:children]
web-eu-west
web-us-east
[eu:vars]
dc=eu-west
[eu:children]
web-eu-west
[us:vars]
dc=us-east
[us:children]
web-us-east

The bellow is working fine in my playbook  :

-- hosts: "{{  hosts | default('web') }}"

Unfortunately we have a case now where we need to combine the dc variable in the default filter , I'm trying the bellow two combinations with errors :

- hosts: "{{ hosts | default('web-'dc) }}"

ERROR! template error while templating string: expected token ',', got 'dc'. String: {{ hosts | default('web-'dc) }}

- hosts: "{{ hosts | default('bid-'+ dc) }}"

ERROR! the field 'hosts' has an invalid value, which appears to include a variable that is undefined. The error was: 'dc' is undefined

What is the right way to concatenate a value and a var using the default filter ?

[Johannes Kastl]

On 05.01.17 15:10 Nicolas G wrote:
> - hosts: "{{ hosts | default('web-'dc) }}"

Try this:

- hosts: "{{ hosts | default([ [ 'web-', dc ] | join ] ) }}"
or
- hosts: "{{ hosts | default([ 'web-', dc ] | join ) }}"

Not sure if you need two sets of square brackets.

Johannes

[Matt Martz]

Your general approach is pretty much correct in your last example:

- hosts: "{{ hosts | default('bid-'+ dc) }}"

Although jinja2 recommends using a `~` instead of `+` for string concatenation, although both will work.

However, the real problem is with your variable.  You have created the `dc` variable in your inventory, which means that it is scoped to the hosts within that group.  Because you are using the `dc` variable in your `hosts` declaration, no hosts have been targeted, and additionally, the `dc` variable is per host, not global.

As such, you cannot use the `dc` variable in a hosts declaration due to variable scoping, and the `dc` variable not being defined at that point.

The only real place to define a variable that can be used in the `hosts` declaration is via the command line via -e/--extra-vars

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Matt Martz
@sivel
sivel.net

[Nicolas G]

Got it Matt , that makes sense.

Thanks .

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