Append a dict to a list of dicts in Ansible based on user configuration - ansible

Question

I want to deploy an application via ansible that has a configurable number of application nodes running via a systemd service. I have a role that manages these services for me but expects the name of the services along with e.g. the priority.
In my playbook the user defines something like this
application_nodes:
- name: "node1"
api_port: 3900
- name: "node2"
api_port: 3910
Therefore I need to append the list that this the systemd role manages. I tried the following
service_list: "{% for node in application_nodes %}{'name': 'application_{{ node.name }}.service', 'priority': 1000}{% endfor %}"
devture_systemd_service_manager_services_list_auto: |
{{
([{{ service_list }}])
}}
This results in the following error
FAILED! => {"msg": "An unhandled exception occurred while templating '{{\n ([{{ service_list }}])\n}}\n'. Error was a <class 'ansible.errors.AnsibleError'>, original message: template error while templating string: expected token ':', got '}'. String: {{\n ([{{ service_list }}])\n}}\n. expected token ':', got '}'"}
I cannot figure out what I did wrong here.
I the end it should work like this (except automatically for every node)
devture_systemd_service_manager_services_list_auto: |
{{
([{'name': 'application_node1.service', 'priority': 1000}])
+
([{'name': 'application_node2.service', 'priority': 1000}])
}}
I also considered something like this
- name: Append services list by nodes
set_fact:
devture_systemd_service_manager_services_list_auto: "{{ devture_systemd_service_manager_services_list_auto + [{'name': 'application_{{ item.name }}.service', 'priority': 1000, 'groups': ['applicationname']}] }}"
loop: "{{ application_nodes }}"
- name: "Print services"
debug:
msg: "services {{ devture_systemd_service_manager_services_list_auto }}"
Where the error is similar to this issue but the solution does not work for me as I want to access a specific key of the dictionary
TASK [custom/base : Print services B] ********************************************************************************************************************************************************************************************************************
fatal: [mydomain]: FAILED! => {"msg": "The task includes an option with an undefined variable. The error was: [{'name': 'application_node2.service', 'priority': 1000, 'groups': ['applicationname']}, {'name': 'application_{{ item.name }}.service', 'priority': 1000, 'groups': ['applicationname']}]: 'item' is undefined. 'item' is undefined. [{'name': 'application_node2.service', 'priority': 1000, 'groups': ['applicationname']}, {'name': 'application_{{ item.name }}.service', 'priority': 1000, 'groups': ['applicationname']}]: 'item' is undefined. 'item' is undefined\n\nThe error appears to be in '/.../roles/custom/base/tasks/add_services.yml': line 11, column 3, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n\n- name: \"Print services B\"\n ^ here\n"}

Answer 1

To start with, the var definition in the role your are using is overly complicated for something as simple as a list of dicts. This is a source of confusion. So to be clear the following expression:
devture_systemd_service_manager_services_list_auto: |
{{
([{'name': 'application_node1.service', 'priority': 1000}])
+
([{'name': 'application_node2.service', 'priority': 1000}])
}}
is actually the exact equivalent of:
devture_systemd_service_manager_services_list_auto:
- name: application_node1.service
priority: 1000
- name: application_node2.service
priority: 1000
The second source of confusion IMO is that you used the term append (which is in Ansible the fact to add more elements to a list) rather than combine (i.e. adding/updating keys in one dict from an other dict).
Those precisions being made, we can fulfill your requirement by:
Extracting the name attribute from each element in the original list
Transform that name so that it matches your expected service name
Append a dict containing that name and the expected priority in relevant keys to a result list
Note that having to transform the name makes it difficult to avoid looping inside a template for the var definition (which we generally tend to avoid in Ansible). But this can still be done in one single expression as demonstrated in the following test playbook:
---
- hosts: localhost
gather_facts: false
vars:
application_nodes:
- name: "node1"
api_port: 3900
- name: "node2"
api_port: 3910
devture_systemd_service_manager_services_list_auto: >-
{%- set result = [] -%}
{%- for node in application_nodes -%}
{%- set service_name = node.name | regex_replace('^(.*)$', 'application_\\1.service') -%}
{{ result.append({'name': service_name, 'priority': 1000}) }}
{%- endfor -%}
{{ result }}
tasks:
- name: Show our list
ansible.builtin.debug:
var: devture_systemd_service_manager_services_list_auto
which gives (relevant task output only)
TASK [Show our list] *********************************************************
ok: [localhost] => {
"devture_systemd_service_manager_services_list_auto": [
{
"name": "application_node1.service",
"priority": 1000
},
{
"name": "application_node2.service",
"priority": 1000
}
]
}

Answer 2

You almost had it in your first try. If you add a few things to your service_list it ends up being a list of dicts -- which is ultimately what you want to append to devture_systemd_service_manager_services_list_auto.
- hosts: all
vars:
application_nodes:
- name: "node1"
api_port: 3900
- name: "node2"
api_port: 3910
tasks:
- set_fact:
# The square brackets before and after the loop make this an actual
# list.
# To make sure that the list items are separated from each other, we
# have to add a comma after each item. Luckily Ansible / Python isn't
# too picky about a comma without a final item. ;-)
service_list: >
[
{% for node in application_nodes %}
{'name': 'application_{{ node.name }}.service', 'priority': 1000},
{% endfor %}"
]
- set_fact:
devture_systemd_service_manager_services_list_auto: >
{{ devture_systemd_service_manager_services_list_auto|default([]) +
service_list }}
- debug:
var: devture_systemd_service_manager_services_list_auto