prometheus: only install different version, unless forced

roles/prometheus/tasks/main.yml

@@ -1,7 +1,21 @@
 ---
+- name: check if installing a different version of prometheus
+  tags:
+    - prometheus
+  shell: "cat {{ prometheus_config }}/.sha256"
+  ignore_errors: yes
+  register: checksum
+
+- name: determine if prometheus {{ prometheus_version}} should be installed
+  tags:
+    - prometheus
+  set_fact:
+    prometheus_install: (checksum.stdout.find(prometheus_sha256) == -1) or (prometheus_force is defined)
+
 - name: download and checksum prometheus {{ prometheus_version }} tarball
   tags:
     - prometheus
+  when: prometheus_install
   get_url:
     url: "{{ prometheus_url }}"
     dest: "{{ prometheus_tgz }}"
@@ -10,6 +24,7 @@
 - name: unpack prometheus tarball
   tags:
     - prometheus
+  when: prometheus_install
   unarchive:
     src: "{{ prometheus_tgz }}"
     dest: "/tmp/"
@@ -18,6 +33,7 @@
 - name: create prometheus user
   tags:
     - prometheus
+  when: prometheus_install
   user:
     name: prometheus
     shell: "/bin/false"
@@ -28,12 +44,12 @@
     - prometheus
   stat:
     path: "/etc/systemd/system/prometheus.service"
-  register: checked
+  register: svccheck
 
 - name: stop prometheus service if it exists
   tags:
     - prometheus
-  when: checked.stat.exists
+  when: svccheck.stat.exists
   service:
     name: prometheus
     state: stopped
@@ -41,6 +57,7 @@
 - name: copy prometheus binaries to /usr/local/bin
   tags:
     - prometheus
+  when: prometheus_install
   command: "cp {{ prometheus_tmp }}/{{ item }} /usr/local/bin/"
   with_items:
     - "prometheus"
@@ -49,6 +66,7 @@
 - name: set permissions on prometheus binaries
   tags:
     - prometheus
+  when: prometheus_install
   file:
     path: "/usr/local/bin/{{ item }}"
     owner: prometheus
@@ -61,6 +79,7 @@
 - name: create prometheus config directory
   tags:
     - prometheus
+  when: prometheus_install
   file:
     path: "{{ prometheus_config }}"
     state: directory
@@ -86,6 +105,7 @@
 - name: create prometheus data directory
   tags:
     - prometheus
+  when: prometheus_install
   file:
     path: "{{ prometheus_data }}"
     state: directory
@@ -116,9 +136,18 @@
 - name: remove temporary prometheus files
   tags:
     - prometheus
+  when: prometheus_install
   file:
     path: "{{ item }}"
     state: absent
   with_items:
     - "{{ prometheus_tmp }}"
     - "{{ prometheus_tgz }}"
+
+- name: create checksum file for prometheus {{ prometheus_version }}
+  tags:
+    - prometheus
+  when: prometheus_install
+  template:
+    src: sha256.j2
+    dest: "{{ prometheus_config }}/.sha256"

roles/prometheus/templates/sha256.j2

@@ -0,0 +1,3 @@
+# {{ ansible_managed }}
+# Remove this file to force ansible to reinstall prometheus {{ prometheus_version }}.
+{{ prometheus_sha256 }}