README: add doc about crons

README.md

@@ -9,6 +9,12 @@ Checks are done by running Icinga/Nagios compatible check plugins inside contain
 
 **Note:** The first plugin detected as installed will be used.
 
+This script also include a set of cron modes to automatically rebuild and deploy containers image of a docker compose project:
+
+-   **check cron (use `--check-mode`):** check if containers need to be updated and marked then to be rebuilt;
+-   **rebuild cron (use `--rebuild-mode`):** rebuild containers marked to be rebuilt;
+-   **deploy cron (use `--deploy-cron`):** deploy rebuilt containers.
+
 ## Installation
 
 ```
@@ -21,6 +27,29 @@ echo "command[check_container_upgrade]=sudo /usr/local/lib/nagios/plugins/check_
 service nagios-nrpe-server reload
 ```
 
+## Configure crons
+
+```bash
+mkdir /var/log/check_container_upgrade
+cat << EOF > /etc/cron.d/containers
+PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+00 2 * * * root /usr/local/lib/nagios/plugins/check_container_upgrade -f /srv/docker/docker-compose.yml --build -v -l /var/log/containers/check_container_upgrade.log --check-cron
+30 2 * * * root /usr/local/lib/nagios/plugins/check_container_upgrade -f /srv/docker/docker-compose.yml --build -v -l /var/log/containers/check_container_upgrade.log --rebuild-cron
+0 4 * * * root /usr/local/lib/nagios/plugins/check_container_upgrade -f /srv/docker/docker-compose.yml --build -v -l /var/log/containers/check_container_upgrade.log --deploy-cron
+30 4 * * * root /usr/bin/docker image prune -a -f > /dev/null
+EOF
+cat << EOF > /etc/logrotate.d/containers
+/var/log/check_container_upgrade/*.log {
+        weekly
+        missingok
+        rotate 53
+        compress
+        copytruncate
+        notifempty
+}
+EOF
+```
+
 ## Usage
 
 ```