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

[Junien F]

README : add paragraph about unlimited_clients

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

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[Benjamin Allot (ballot)]

LGTM

review: Approve

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

Change successfully merged at revision 7e28462be0a3c2dece3cbac743264e83d339a7c5

diff --git a/README.md b/README.md
index 15d5628..972ff85 100644
--- a/README.md
+++ b/README.md
@@ -1,5 +1,5 @@
 Overview
---------
+========
 
 Network Time Protocol (NTP) is a network-based time service to ensure
 synchronization of time across a network of computers.  It is defined in
@@ -7,7 +7,7 @@ RFC5905.
 
 
 Usage
------
+=====
 
 The ntp charm is a subordinate charm which is designed for use with other
 principal charms.  In its basic mode, the ntp charm is used to configure NTP
@@ -23,7 +23,7 @@ several options.
 
 
 Manual
-======
+------
 
 If you already have a set of reliable, non-juju NTP servers in your network,
 simply configure them as sources or peers and disable the default list of pool
@@ -37,7 +37,7 @@ Sources, peers, and pools should be space-separated.
 
 
 Multiple strata
-===============
+---------------
 
 In network environments where general outbound network access to the Internet
 is not avaliable or you don't have a good internal time source such as an
@@ -60,7 +60,7 @@ On other juju units which do not have outbound NTP access:
 
 
 Auto peers
-==========
+----------
 
 Auto peers implements multiple strata automatically, by testing upstream NTP
 connectivity, selecting the units with the best connectivity to comprise
@@ -73,8 +73,23 @@ those units.
     juju set ntp auto_peers=true
 
 
+Rate-limited clients
+--------------------
+
+By default, ntpd puts a per-IP rate-limit on client requests. This can be
+problematic if, for example, you have a lot of hosts NATed behind a single IP.
+You can configure ntpd to not rate-limit requests coming from specific IPs or
+networks by using the `unlimited_clients` config option. It is a space-separated
+list of IPs and networks. Networks must be specified in the `<network_address>
+mask <network_mask>` form. For example :
+
+    juju config ntp unlimited_clients="1.2.3.4,192.168.0.0 mask 255.255.0.0"
+
+Note that this option is ignored when the NTP implementation is chrony.
+
+
 NTP Implementations
--------------------
+===================
 
 Under Ubuntu 17.10 (Artful Aardvark) and earlier, the default implementation
 of NTP is ntpd, from the Network Time Foundation.  Ubuntu 18.04 (Bionic
@@ -83,7 +98,7 @@ are also reflected in this charm.
 
 
 Monitoring
-----------
+==========
 
 This charm may be related to the NRPE charm for monitoring by Nagios.
 The telegraf charm also includes support for gathering NTP metrics.