There's a way to template a variable in ansible - templates

Question

applications:
appA:
someDB:
enable: true
datadir: '/var/lib/postgresql/11/appA'
appB:
someDB:
enable: true
datadir: '/var/lib/postgresql/11/appB'
- ansible.builtin.set_fact:
clusters: "{{ clusters + [ item ] }}"
when: applications.{{ item }}.someDB.enable
loop:
- appA
- appB
- ansible.builtin.shell: |
pg_createcluster \
-d {{ aplications.item.someDB.datadir }}
when: item == 'appA'
loop: "{{ clusters }}"
Is there a simple way to make ansible do substitutions inside a var ? Like some precedence operand.
In the loop: item == appA
so, {{ aplications.item.someDB.datadir }} is like this {{ aplications.appA.someDB.datadir }}, and autmatocally is its content is: '/var/lib/postgresql/11/appA' and so on.
Probably I'm using the wrong approach, but seems reasonable to me do that.
Thank's for anyu help.

Answer 1

The applications variable can be flattened, so it will be easier to set the conditions for the task
applications:
- name: appA
someDB:
enable: true
datadir: '/var/lib/postgresql/11/appA'
- name: appB
someDB:
enable: true
datadir: '/var/lib/postgresql/11/appB'
- name: Create PG cluster
ansible.builtin.shell: >
pg_createcluster
-d {{ item.someDB.datadir }}
when:
- item.name == 'appA'
- item.someDB.enable
loop: "{{ applications }}"
Some comments:
Adding a unique name to the task will make it easier to debug your playbooks, specially when you have a long playbook or role
using > in shell will take care to collapse the instructions as a single line, so you won't need the slash
Usually to create a postgress database, you would prefer to use the postgresql_db Ansible module; the -d <directory> is preferred to be set in the configuration file, so you wouldn't need it as an argument.

Answer 2

Create the list of enabled clusters
clusters: "{{ applications|dict2items|
json_query('[?value.someDB.enable].key') }}"
gives
clusters:
- appA
- appB
Then, the task below creates the run-strings you want
- debug:
msg: "pg_createcluster -d {{ applications[item].someDB.datadir }}"
loop: "{{ clusters }}"
gives (abridged)
msg: pg_createcluster -d /var/lib/postgresql/11/appA
msg: pg_createcluster -d /var/lib/postgresql/11/appB
Example of a complete playbook for testing
- hosts: localhost
vars:
applications:
appA:
someDB:
enable: true
datadir: '/var/lib/postgresql/11/appA'
appB:
someDB:
enable: true
datadir: '/var/lib/postgresql/11/appB'
clusters: "{{ applications|dict2items|
json_query('[?value.someDB.enable].key') }}"
tasks:
- debug:
var: clusters
- debug:
msg: "pg_createcluster -d {{ applications[item].someDB.datadir }}"
loop: "{{ clusters }}"
Notes:
You can get both the key and the value by substitution
- debug:
msg: "{{ _key }}: {{ _val }}"
loop:
- appA
- appB
when: applications[item].someDB.enable
vars:
_key: "applications.{{ item }}.someDB.datadir"
_val: "{{ applications[item].someDB.datadir }}"
gives (abridged)
msg: 'applications.appA.someDB.datadir: /var/lib/postgresql/11/appA'
msg: 'applications.appB.someDB.datadir: /var/lib/postgresql/11/appB'
Create a dictionary to simplify the searching
app_datadir: "{{ dict(applications|dict2items|
json_query('[].[key, value.someDB.datadir]')) }}"
gives
app_datadir:
appA: /var/lib/postgresql/11/appA
appB: /var/lib/postgresql/11/appB
Use this dictionary "to make Ansible do substitutions". For example,
- debug:
msg: "applications.{{ item }}.someDB.datadir: {{ app_datadir[item] }}"
loop:
- appA
- appB
gives (abridged)
msg: 'applications.appA.someDB.datadir: /var/lib/postgresql/11/appA'
msg: 'applications.appB.someDB.datadir: /var/lib/postgresql/11/appB'
Example of a complete playbook for testing
- hosts: localhost
vars:
applications:
appA:
someDB:
enable: true
datadir: '/var/lib/postgresql/11/appA'
appB:
someDB:
enable: true
datadir: '/var/lib/postgresql/11/appB'
app_datadir: "{{ dict(applications|dict2items|
json_query('[].[key, value.someDB.datadir]')) }}"
tasks:
- debug:
var: app_datadir
- debug:
msg: "applications.{{ item }}.someDB.datadir: {{ app_datadir[item] }}"
loop:
- appA
- appB
You can also create the dictionary app_enable
app_enable: "{{ dict(applications|dict2items|
json_query('[].[key, value.someDB.enable]')) }}"
gives
app_enable:
appA: true
appB: true
and use it in the condition. For example,
- debug:
msg: "applications.{{ item }}.someDB.datadir: {{ app_datadir[item] }}"
loop:
- appA
- appB
when: app_enable[item]