Merge ~jacekn/prometheus-charm:lp1610928 into prometheus-charm:master

[Jacek Nykis]

Stop unnecessary prometheus restarts. Fixes LP1610928
Switch prometheus_registration_listen stanzas to safer config.get method, this also fixes tests

[David Lawson (deej)]

+1

review: Approve

diff --git a/reactive/prometheus.py b/reactive/prometheus.py
index 558bafc..4dfb9cc 100644
--- a/reactive/prometheus.py
+++ b/reactive/prometheus.py
@@ -60,7 +60,7 @@ def install_packages():
     fetch.apt_update()
     fetch.apt_install(PKGNAMES)
     config = hookenv.config()
-    if config['prometheus_registration_listen']:
+    if config.get('prometheus_registration_listen', False):
         fetch.apt_install('promreg')
     remove_state('prometheus.do-install')
 
@@ -101,7 +101,7 @@ def write_prometheus_config_yml():
         'evaluation_interval': config['evaluation-interval'],
         'static_targets': static_targets,
         'private_address': hookenv.unit_get('private-address'),
-        'promreg': config['prometheus_registration_listen'] != '',
+        'promreg': config.get('prometheus_registration_listen', False),
         'monitor_name': config.get('monitor_name', default_monitor_name),
         'jobs': target_jobs,
         'federate': federate_config,
@@ -122,7 +122,7 @@ def write_prometheus_config_yml():
            )
     validate_config()
 
-    if config['prometheus_registration_listen']:
+    if config.get('prometheus_registration_listen', False):
         render(source='promreg.yaml.j2',
                target='/etc/prometheus/promreg.yaml',
                context=config,
@@ -259,7 +259,7 @@ def update_prometheus_no_targets():
 def update_prometheus_targets(target):
     services = target.services()
     related_targets = []
-    for service in services:
+    for service in sorted(services, key=lambda k: k['service_name']):
         targets = []
         for unit in service['hosts']:
             hookenv.log('{} has a unit {}:{}'.format(
@@ -268,7 +268,7 @@ def update_prometheus_targets(target):
                 unit['port']), level='debug')
             targets.append('{hostname}:{port}'.format(**unit))
         related_targets.append({'job_name': service['service_name'],
-                                'targets': targets})
+                                'targets': sorted(targets)})
 
     unitdata.kv().set('target_jobs', related_targets)
     set_state('prometheus.do-check-reconfig')