Merge ~paulgear/ntp-charm/+git/ntp-charm:master into ntp-charm:master

[Paul Gear]

This change (from server to pool in /etc/ntp.conf) will produce the following effects:
- on trusty, a longer list of peers will be selected from the pool at service start time
- on xenial, one server from each pool will be selected at start time, and poor quality/unresponsive servers will be replaced with new servers periodically

[Junien F (axino)]

This looks good.

Does precise's ntp understand "pool" ?

[Stuart Bishop (stub)]

Per metadata.yaml, the charm does not support precise so we don't care about that.

Looks good. One trivial point inline.

review: Approve

[Junien F (axino)]

+1

review: Approve

[Paul Gear (paulgear)]

> This looks good.
>
> Does precise's ntp understand "pool" ?

precise's ntp does understand pool, so this should still work even if forced onto precise.

[Paul Gear (paulgear)]

> ...
> Looks good. One trivial point inline.

Updated to use > except in one case where indentation is required; not sure if there's a better way to do that with yaml...

diff --git a/config.yaml b/config.yaml
index 13929ea..cadefa1 100644
--- a/config.yaml
+++ b/config.yaml
@@ -2,11 +2,17 @@ options:
   source:
     default: ""
     type: string
-    description: Space separated list of NTP servers to use as source for time.
+    description: >
+        Space-separated list of NTP servers to use as sources for time.
+        Servers are added using the 'pool' directive to allow recent ntp
+        versions to automatically drop poor quality sources from the
+        running configuration and select new ones from the pool.
   peers:
     default: ""
     type: string
-    description: Space separated list of NTP servers to use as peers for time.
+    description: >
+        Space-separated list of NTP servers to use as peers for time.
+        Peers are allowed to query the local NTP server via ntpq.
   nagios_context:
     default: "juju"
     type: string
@@ -20,24 +26,26 @@ options:
   nagios_servicegroups:
     default: ""
     type: string
-    description: |
+    description: >
         A comma-separated list of nagios servicegroups.
         If left empty, the nagios_context will be used as the servicegroup.
   nagios_ntpmon_checks:
     default: "offset peers reachability sync"
     type: string
-    description: |
+    description: >
         A space-separated list of nagios ntpmon checks to enable.
         Options are "offset peers reachability sync"; if all are specified,
         they are combined into a single check; leave empty for no checks.
   auto_peers:
     default: false
     type: boolean
-    description:
+    description: >
         Automatically peer with other units in the same service.
         DEPRECATED.  Please consider using the ntpmaster charm to provide
         sufficient peers for your environment in favour of auto_peers.
   use_iburst:
     default: true
     type: boolean
-    description: Use iburst for all servers, not just ntpmaster.
+    description: >
+        Use iburst for all peers/sources, not just those received via the
+        master relation.
diff --git a/templates/ntp.conf b/templates/ntp.conf
index 605c880..882155a 100644
--- a/templates/ntp.conf
+++ b/templates/ntp.conf
@@ -6,12 +6,13 @@ filegen peerstats file peerstats type day enable
 filegen clockstats file clockstats type day enable
 restrict -4 default kod notrap nomodify nopeer noquery
 restrict -6 default kod notrap nomodify nopeer noquery
+restrict source notrap nomodify noquery
 restrict 127.0.0.1
 restrict ::1
 {% for peer in peers %}restrict {{ peer.name }} kod notrap nomodify
 {% endfor %}
 # SERVERS
-{% for server in servers %}server {{ server.name }} {{ server.iburst }}
+{% for server in servers %}pool {{ server.name }} {{ server.iburst }}
 {% endfor %}
 # PEERS
 {% for peer in peers %}peer {{ peer.name }} {{ peer.iburst }}