Ntp

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 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 in service units to talk directly to a set of NTP time sources:

juju deploy cs:ntp
juju add-relation ntp myservice

By default this charm uses the standard set of NTP pool servers which are configured in Ubuntu. In the event that you don't wish every juju unit on your network to talk directly to the public NTP pool on the Internet, there are 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 servers. For example:

juju set ntp source="myatomicclock.local.net"
juju set ntp peers="ntp1.local.net ntp2.local.net ntp3.local.net"
juju set ntp pools=""

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 atomic clock, you can use selected juju units to act as an NTP service for other units.

On machines which do have outbound NTP access to the Internet:

juju deploy cs:ubuntu --num-units=4
juju deploy cs:ntp ntp-stratum2
juju add-relation ubuntu ntp-stratum2

On other juju units which do not have outbound NTP access:

juju deploy my-service
juju deploy cs:ntp ntp-stratum3
juju add-relation my-service ntp-stratum3
juju add-relation ntp-stratum2 ntp-stratum3
juju set ntp source="" peers="" pools=""

Auto peers

Auto peers implements multiple strata automatically, by testing upstream NTP connectivity, selecting the units with the best connectivity to comprise the upstream stratum, and configuring the remaining hosts to receive time from those units.

juju deploy my-service
juju deploy cs:ntp
juju add-relation my-service ntp
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 comma-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 Beaver) moves to chrony as the default NTP implementation. These decisions 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.