add an nrpe-external-master relation, with a basic check (systemd service is running)

layer.yaml

@@ -1,11 +1,13 @@
 repo: https://github.com/juju-solutions/layer-etcd.git
 includes:
   - 'layer:basic'
-  - 'layer:tls-client'
-  - 'layer:leadership'
   - 'layer:debug'
+  - 'layer:leadership'
+  - 'layer:nagios'
+  - 'layer:tls-client'
   - 'interface:etcd'
   - 'interface:etcd-proxy'
+  - 'interface:nrpe-external-master'
 options:
   basic:
     packages: ['rsync']

reactive/etcd.py

@@ -25,6 +25,7 @@
 from charmhelpers.core import host
 from charmhelpers.fetch import apt_update
 from charmhelpers.fetch import apt_install
+from charmhelpers.contrib.charmsupport import nrpe
 
 from etcdctl import EtcdCtl
 from etcdctl import get_connection_string
@@ -505,6 +506,47 @@ def read_tls_cert(cert):
         return data
 
 
+@when('nrpe-external-master.available')
+@when_not('nrpe-external-master.initial-config')
+def initial_nrpe_config(nagios=None):
+    set_state('nrpe-external-master.initial-config')
+    update_nrpe_config(nagios)
+
+
+@when('etcd.installed')
+@when('nrpe-external-master.available')
+@when_any('config.changed.nagios_context',
+          'config.changed.nagios_servicegroups')
+def update_nrpe_config(unused=None):
+    # List of systemd services that will be checked
+    services = ('etcd',)
+
+    # The current nrpe-external-master interface doesn't handle a lot of logic,
+    # use the charm-helpers code for now.
+    hostname = nrpe.get_nagios_hostname()
+    current_unit = nrpe.get_nagios_unit_name()
+    nrpe_setup = nrpe.NRPE(hostname=hostname, primary=False)
+    nrpe.add_init_service_checks(nrpe_setup, services, current_unit)
+    nrpe_setup.write()
+
+
+@when_not('nrpe-external-master.available')
+@when('nrpe-external-master.initial-config')
+def remove_nrpe_config(nagios=None):
+    remove_state('nrpe-external-master.initial-config')
+
+    # List of systemd services for which the checks will be removed
+    services = ('etcd',)
+
+    # The current nrpe-external-master interface doesn't handle a lot of logic,
+    # use the charm-helpers code for now.
+    hostname = nrpe.get_nagios_hostname()
+    nrpe_setup = nrpe.NRPE(hostname=hostname, primary=False)
+
+    for service in services:
+        nrpe_setup.remove_check(shortname=service)
+
+
 def volume_is_mounted(volume):
     ''' Takes a hardware path and returns true/false if it is mounted '''
     cmd = ['df', '-t', 'ext4']