includer.yml

apiVersion: v1
kind: ConfigMap
metadata:
  name: test-rules
  namespace: monitoring
data:
  node.rules.yml: |-
    {{ lookup('template', 'template.j2')|indent(4) }}

play.yml

- hosts: localhost

  tasks:
    - set_fact:
        resources: []

    - set_fact:
        resources: >-
          {{ resources + lookup('template', item) | from_yaml_all | list }}
      loop:
        - includer.yml

    - include_tasks: task.yml
      loop: "{{ resources }}"

task.yml

- debug:
    var: item

template.j2

groups:
  - name: node.rules
    rules:
    - alert: node.loadaverage
      expr: (node_load5 / count(node_cpu_seconds_total{job="aws-nodes",mode="system"}) WITHOUT (cpu, mode)) > 20
      for: 2m
      labels:
        service: k8s
        severity: INFO
      annotations:
        description: '{{ '{{ $labels.instance }}' }}: The 5 minute average load is high: {{ '{{ $value | printf "%.2f" }}' }}'
        summary: '{{ '{{ $labels.instance }}' }}: High load average detected'