Nested variables and regex_replace()

[Josh Smift]

I have some variables like 'service', which can be "abc" or "xyz", and
'site', which can be "bos" or "sfo", on different hosts. I have hosts
whose FQDNs are like service-site-thing-N.site.service.care.com, which
have those those variables set accordingly, in a group like 'things'.

My use case is that I want to create CNAME records, using the route53
module, for names like thing-N.site.service.care.com, so that if you're on
a host with site.service.care.com in its resolv.conf search path, you can
refer to "thing-N" and have that resolve to service-site-thing-N.

For now, to take the route53 aspect out of the equation (I just mentioned
that for context), I'm just debugging, and it works if I hardcode the
services and sites, but not if I try to use the variables.

Here's a playbook:

- hosts: things

vars: { service="abc", site="bos" }

tasks:
- debug: msg={{ ansible_hostname | regex_replace("^abc-bos-", '') }}
- debug: msg={{ ansible_hostname | regex_replace("^{{service}}-{{site}}-", '') }}

Here's what that does:

TASK: [debug msg={{ ansible_hostname | regex_replace("^abc-bos-", '') }}] *****
ok: [abc-bos-thing-01] => {
"msg": "thing-01"
}
ok: [abc-bos-thing-02] => {
"msg": "thing-02"
}

TASK: [debug msg={{ ansible_hostname | regex_replace("^{{service}}-{{site}}-", '') }}] ***
ok: [abc-bos-thing-01] => {
"msg": "abc-bos-thing-01"
}
ok: [abc-bos-thing-02] => {
"msg": "abc-bos-thing-02"
}

I was hoping the second one would be the same as the first. I tried a
couple of variations on the syntax of the regex_replace in the second
case, but no luck.

I have the same problem if I try to use the

{{ ansible_hostname | regex_replace("^{{service}}-{{site}}-", '') }}

construction when I call the route53 module -- the regexp isn't actually
replaced.

Is there another/better way to do this?

-Josh (j...@care.com)



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[Matt Martz]

The problem is that cannot nest jinja brackets inside of brackets.  Your following example:

  {{ ansible_hostname | regex_replace("^{{service}}-{{site}}-", '') }}

Should probably be:

  {{ ansible_hostname | regex_replace("^" + service + "-" + site + "-", '') }}

Inside of {{ }} variables are already expanded.

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Matt Martz
@sivel
sivel.net

[Josh Smift]

MM> The problem is that cannot nest jinja brackets inside of brackets.

Ah! Right, because brackets mean "Jinja", not just "variable". Still new
here. :^)

MM> Your following example:
MM>
MM> {{ ansible_hostname | regex_replace("^{{service}}-{{site}}-", '') }}
MM>
MM> Should probably be:
MM>
MM> {{ ansible_hostname | regex_replace("^" + service + "-" + site + "-", '')
MM> }}
MM>
MM> Inside of {{ }} variables are already expanded.

That works! Well, it turns out I was defining my variables wrong in this
example, but when I changed

vars: { service="abc", site="bos" }

to the less wrong

vars:
service: "abc"
site: "bos"

it worked perfectly, both in the debug example and in the actual route53
module.

Yay Ansible! Yay ansible-project! Thanks Matt!