Merge ~aggkolaitis/charm-nrpe:nrpe_bind_all_option into ~nrpe-charmers/charm-nrpe:master

[Angelos Kolaitis]

Added `nrpe_bind_all` boolean option.

LP: #1849800

NRPE binds on all network interfaces by default.

The introduced option allows configuring NRPE to only bind on the interface required by Nagios (which should default to the private address of the machine). The default value is True, to maintain backwards compatibility (binding on all interfaces by default) with existing deployments

[🤖 Canonical IS Merge Bot (canonical-is-mergebot)]

This merge proposal is being monitored by mergebot. Change the status to Approved to merge.

[Stuart Bishop (stub)]

The new option looks fine.

I will point out that the default of the private address is incorrect though; since cross model relations servers need to look up the assigned bind addresses (per Juju network spaces, cross model relations, and all that new fun stuff). That is for a future branch though.

review: Approve

[Andrea Ieri (aieri)]

The code looks good, but I feel that it would be more idiomatic in Juju to try to obtain as much information as possible through the model (i.e. via relations), rather than from the operator. Specifically, we already configure allowed_hosts to be the list of IPs and networks we expect connections from. That information could be further leveraged to automatically determine which interfaces we should be binding to.

review: Disapprove

Unmerged commits

3867e67... by Angelos Kolaitis on 2019-10-25

Added nrpe_bind_all option

diff --git a/config.yaml b/config.yaml
index 44a6680..031cc10 100644
--- a/config.yaml
+++ b/config.yaml
@@ -1,4 +1,9 @@
 options:
+  nrpe_bind_all:
+    default: True
+    type: boolean
+    description: |
+        Allow NRPE to listen on all interfaces.
   nagios_master:
     default: "None"
     type: string
diff --git a/hooks/nrpe_helpers.py b/hooks/nrpe_helpers.py
index abd6398..c5d04df 100644
--- a/hooks/nrpe_helpers.py
+++ b/hooks/nrpe_helpers.py
@@ -267,6 +267,9 @@ class NagiosInfo(dict):
         self['dont_blame_nrpe'] = '1' if hookenv.config('dont_blame_nrpe') else '0'
         self['debug'] = '1' if hookenv.config('debug') else '0'
 
+        self['nrpe_bind_all'] = hookenv.config('nrpe_bind_all')
+
+
 
 class RsyncEnabled(helpers.RelationContext):
 
diff --git a/templates/nrpe.tmpl b/templates/nrpe.tmpl
index d7e37cd..ab65696 100644
--- a/templates/nrpe.tmpl
+++ b/templates/nrpe.tmpl
@@ -2,6 +2,7 @@
 # This file is managed by Juju
 #--------------------------------------------------------
 
+{% if not nrpe_bind_all %}server_address={{ nagios_ipaddress }}{% endif %}
 server_port={{ server_port }}
 allowed_hosts={{ external_nagios_master }},{{ monitor_allowed_hosts }}
 nrpe_user=nagios