Merge ~paulgear/charm-nrpe/+git/nrpe-charm:master into ~nrpe-charmers/charm-nrpe:master

[Paul Gear]

I spent a sizable chunk of a large ticket a few months back debugging why adding a relation made the nrpe charm generate incorrect hostnames when it had previously had correct ones. I think this is due to a timing issue because of when the nagios hostname is obtained vs. when it is used, and this change seems to help, but I'm not familiar enough with the services framework to know whether this is just luck.

[William Grant (wgrant)]

This seems like a reasonable change. I'm not sure why the host definition would need a rewrite on nrpe-config, but it empirically has seemed to be the case in the past, and neither change can make things worse.

review: Approve

[Paul Gear (paulgear)]

This branch is still buggy; I've tested it and it causes host files to be removed on upgrade - still trying to work out why.

[Paul Gear (paulgear)]

I've pushed a new revision which fixes the host export file removal issue, and tested deploy on xenial and upgrade-charm on trusty & xenial.

[William Grant (wgrant)]

review: Approve

[Stuart Bishop (stub)]

'ick. I'd forgotten service manager.

review: Approve

[Paul Gear (paulgear)]

This might fix lp:1671707

diff --git a/hooks/nrpe_utils.py b/hooks/nrpe_utils.py
index 89f8092..ae83158 100644
--- a/hooks/nrpe_utils.py
+++ b/hooks/nrpe_utils.py
@@ -4,8 +4,10 @@ import glob
 
 from charmhelpers import fetch
 from charmhelpers.core import host
-from charmhelpers.core.templating import render
 from charmhelpers.core import hookenv
+from charmhelpers.core.services import helpers
+from charmhelpers.core.services.base import ManagerCallback
+from charmhelpers.core.templating import render
 
 import nrpe_helpers
 
@@ -115,7 +117,7 @@ def process_local_monitors():
 
 def update_nrpe_external_master_relation(service_name):
     """
-    Send updated nagsios_hostname to charms attached to nrpe_external_master
+    Send updated nagios_hostname to charms attached to nrpe_external_master
     relation.
     """
     principle_relation = nrpe_helpers.PrincipleRelation()
@@ -134,3 +136,27 @@ def update_monitor_relation(service_name):
             relation_id=rid,
             relation_settings=monitor_relation.provide_data()
         )
+
+
+class ExportManagerCallback(ManagerCallback):
+
+    """
+    This class exists in order to defer lookup of nagios_hostname()
+    until the template is ready to be rendered.  This should reduce the
+    incidence of incorrectly-rendered hostnames in /var/lib/nagios/exports.
+    See charmhelpers.core.services.base.ManagerCallback and
+    charmhelpers.core.services.helpers.TemplateCallback for more background.
+    """
+
+    def __call__(self, manager, service_name, event_name):
+        nag_hostname = nrpe_helpers.PrincipleRelation().nagios_hostname()
+        target = '/var/lib/nagios/export/host__{}.cfg'.format(nag_hostname)
+        renderer = helpers.render_template(
+            source='export_host.cfg.tmpl',
+            target=target,
+            perms=0o644,
+        )
+        renderer(manager, service_name, event_name)
+
+
+create_host_export_fragment = ExportManagerCallback()
diff --git a/hooks/services.py b/hooks/services.py
index 9034981..543bcc6 100644
--- a/hooks/services.py
+++ b/hooks/services.py
@@ -8,7 +8,6 @@ import nrpe_helpers
 
 def manage():
     config = hookenv.config()
-    nag_hostname = nrpe_helpers.PrincipleRelation().nagios_hostname()
     manager = ServiceManager([
         {
             'service': 'nrpe-install',
@@ -28,6 +27,7 @@ def manage():
             'data_ready': [
                 nrpe_utils.update_nrpe_external_master_relation,
                 nrpe_utils.update_monitor_relation,
+                nrpe_utils.create_host_export_fragment,
                 nrpe_utils.render_nrped_files,
                 helpers.render_template(
                     source='nrpe.tmpl',
@@ -51,12 +51,7 @@ def manage():
                     source='rsync-juju.d.tmpl',
                     target='/etc/rsync-juju.d/010-nrpe-external-master.conf'
                 ),
-                helpers.render_template(
-                    source='export_host.cfg.tmpl',
-                    target='/var/lib/nagios/export/'
-                           'host__{}.cfg'.format(nag_hostname),
-                    perms=0o644,
-                ),
+                nrpe_utils.create_host_export_fragment,
             ],
             'start': [nrpe_utils.restart_rsync],
         },