systemd unit for the prometheus server. Also, do not overwrite the configuration file.

prometheus/defaults/main.yml

@@ -1,6 +1,6 @@
 ---
 prometheus_install: True
-prometheus_version: 2.1.0
+prometheus_version: 2.2.1
 prometheus_dir: 'prometheus-{{ prometheus_version }}.linux-amd64'
 prometheus_file: '{{ prometheus_dir }}.tar.gz'
 prometheus_download_url: 'https://github.com/prometheus/prometheus/releases/download/v{{ prometheus_version }}/{{ prometheus_file }}'

prometheus/files/prometheus.systemd

@@ -0,0 +1,16 @@
+[Unit]
+Description=Prometheus - Prometheus metrics collector.
+Documentation=https://prometheus.io/docs/introduction/overview/
+After=network.target
+
+[Service]
+Type=simple
+User={{ prometheus_user }}
+Group={{ prometheus_user }}
+EnvironmentFile=/etc/default/prometheus
+ExecStart=${PROMETHEUS_CMD} --config.file=${PROMETHEUS_CONF} --storage.tsdb.path=${PROMETHEUS_DATADIR} --log.level=${PROMETHEUS_LOGLEVEL} ${PROMETHEUS_OPTS}
+Restart=on-failure
+
+[Install]
+WantedBy=multi-user.target
+

prometheus/tasks/main.yml

@@ -26,15 +26,21 @@
       notify: Restart prometheus
 
     - name: Install the prometheus configuration
-      template: src=prometheus.yml.j2 dest={{ prometheus_confdir }}/prometheus.yml
+      template: src=prometheus.yml.j2 dest={{ prometheus_confdir }}/prometheus.yml force=no
       notify: Reload prometheus
 
-    - name: Install the prometheus upstart script
-      copy: src=prometheus.upstart dest=/etc/init/prometheus.conf mode=0644 owner=root group=root
-
     - name: Install the prometheus defaults
       template: src=prometheus.default.j2 dest=/etc/default/prometheus mode=0644 owner=root group=root
 
+    - name: Install the prometheus upstart script
+      copy: src=prometheus.upstart dest=/etc/init/prometheus.conf mode=0644 owner=root group=root
+      when: ansible_service_mgr != 'systemd'
+
+    - name: Install the prometheus server systemd unit
+      copy: src=prometheus.systemd dest=/etc/systemd/system/prometheus.service mode=0644 owner=root group=root
+      when: ansible_service_mgr == 'systemd'
+      notify: systemd reload
+
     - name: Ensure that prometheus is started and enabled
       service: name=prometheus state=started enabled=yes