use /etc/default/prometheus to configure args

defaults/main.yml

@@ -30,3 +30,9 @@ prometheus_download_url: >-
 
 # Valid options: [ remote, local ]
 download_mode: remote
+
+prometheus_args: >-
+  --config.file={{ prometheus_etc_path }}/prometheus.yml
+  --storage.tsdb.path={{ prometheus_data_path }}
+  --web.console.templates={{ prometheus_bin_path }}/consoles
+  --web.console.libraries={{ prometheus_bin_path }}/console_libraries

molecule/lxc/side_effect.yml

@@ -0,0 +1,13 @@
+---
+- name: check prometheus status
+  hosts: all
+  tasks:
+    - name: check the prometheus services
+      uri:
+        url: http://localhost:9090/api/v1/status/config
+      register: check_prometheus
+      retries: 3
+      delay: 3
+      until:
+        - check_prometheus.status == 200
+        - check_prometheus.json.status == 'success'

tasks/config.yml

@@ -7,6 +7,7 @@
   with_items:
     - "{{ prometheus_etc_path }}"
     - "{{ prometheus_etc_path }}/rules"
+    - /etc/default
 
 - name: ensure data folder
   file:
@@ -16,6 +17,19 @@
     owner: "{{ prometheus_runas_user }}"
     group: "{{ prometheus_runas_user }}"
 
+- name: copy /etc/dfault/prometheus file
+  template:
+    src: "{{ item }}"
+    dest: /etc/default/prometheus
+  with_first_found:
+    - files:
+        - "default_prometheus.j2"
+      paths:
+        - "{{ playbook_dir }}/templates/{{ role_name }}"
+        - "{{ role_path }}/templates"
+  notify:
+    - restart prometheus service
+
 - name: copy prometheus.yml file
   vars:
     filename: prometheus.yml

tasks/main.yml

@@ -11,5 +11,4 @@
     name: prometheus
     state: started
     enabled: true
-  ignore_errors: true
 # vim:ft=yaml

templates/default_prometheus.j2

@@ -0,0 +1 @@
+ARGS="{{ prometheus_args }}"

templates/prometheus.service.j2

@@ -1,15 +1,15 @@
 [Unit]
-Description=prometheus service
+Description=Monitoring system and time series database
+Documentation=https://prometheus.io/docs/introduction/overview/
 
 [Service]
-Type=simple
+Restart=always
+EnvironmentFile=/etc/default/prometheus
+ExecStart={{ prometheus_bin_path }}/prometheus $ARGS
 ExecReload=/bin/kill -HUP $MAINPID
-ExecStart={{ prometheus_bin_path }}/prometheus \
-  --config.file={{ prometheus_etc_path }}/prometheus.yml \
-  --storage.tsdb.path={{ prometheus_data_path }} \
-  --web.console.templates={{ prometheus_bin_path }}/consoles \
-  --web.console.libraries={{ prometheus_bin_path }}/console_libraries
 User={{ prometheus_runas_user }}
+TimeoutStopSec=20s
+SendSIGKILL=no
 
 [Install]
-WantedBy=default.target
+WantedBy=multi-user.target