Merge ~mpontillo/maas:chrony-xleave-hwtimestamp--bug-1789872 into maas:master

[Mike Pontillo]

LP: #1789872 - Configure chrony with xleave and hwtimestamp.

This change is relatively straightforward and simple, but before we consider landing this I'll be running some end-to-end tests to ensure it behaves correctly, especially when interacting with non-interleaved-mode servers, and on setups that have no hope of ever supporting hardware timestamps, such as MAAS running in VMs or containers.

[Andres Rodriguez (andreserl)]

lgtm!

review: Approve

[MAAS Lander (maas-lander)]

UNIT TESTS
-b chrony-xleave-hwtimestamp--bug-1789872 lp:~mpontillo/maas/+git/maas into -b master lp:~maas-committers/maas

STATUS: FAILED
LOG: http://maas-ci-jenkins.internal:8080/job/maas/job/branch-tester/3836/console
COMMIT: 020b8c508da788736ff3d5f6a286e016f8da31f5

review: Needs Fixing

86fed2b... by Mike Pontillo on 2018-09-04

Format imports.

a2c946f... by Mike Pontillo on 2018-09-04

Add comments.

[MAAS Lander (maas-lander)]

UNIT TESTS
-b chrony-xleave-hwtimestamp--bug-1789872 lp:~mpontillo/maas/+git/maas into -b master lp:~maas-committers/maas

STATUS: SUCCESS
COMMIT: a2c946f8491a88c961184e297eee0dd80910ab7f

review: Approve

[Mike Pontillo (mpontillo)]

I tested this change locally using a combination of configurations including chrony running on metal with hardware timestamp support, and interoperability with a version of chrony on Ubuntu 16.04 (which doesn't support hardware timestamps or interleaved mode), and chrony running in LXD containers. It doesn't appear that this configuration will cause problems in any of the above situations, so I'm comfortable landing this.

diff --git a/src/provisioningserver/ntp/config.py b/src/provisioningserver/ntp/config.py
index d55d2fc..d3af172 100644
--- a/src/provisioningserver/ntp/config.py
+++ b/src/provisioningserver/ntp/config.py
@@ -110,14 +110,21 @@ def _render_ntp_maas_conf(servers, peers, offset):
     :param offset: A relative stratum used when calculating the stratum for
         orphan mode (https://chrony.tuxfamily.org/doc/3.2/chrony.conf.html).
     """
-    lines = ["# MAAS NTP configuration."]
+    lines = [
+        "# MAAS NTP configuration.",
+        # LP: #1789872 - Use hardware timestamps (on interfaces where it is
+        # available).
+        "hwtimestamp *",
+    ]
     servers = map(normalise_address, servers)
     lines.extend(
         "%s %s iburst" % (
             ("server" if isinstance(server, IPAddress) else "pool"), server)
         for server in servers)
     peers = map(normalise_address, peers)
-    lines.extend("peer %s" % peer for peer in peers)
+    # Note: `xleave` is needed here in order to take advantage of the increased
+    # accuracy that comes with enabling hardware timestamps.
+    lines.extend("peer %s xleave" % peer for peer in peers)
     # Chrony provides a special 'orphan' mode that is compatible
     # with ntpd's 'tos orphan' mode. (see
     # https://chrony.tuxfamily.org/doc/devel/chrony.conf.html)
diff --git a/src/provisioningserver/ntp/tests/test_config.py b/src/provisioningserver/ntp/tests/test_config.py
index 89ba737..5499b63 100644
--- a/src/provisioningserver/ntp/tests/test_config.py
+++ b/src/provisioningserver/ntp/tests/test_config.py
@@ -17,6 +17,7 @@ from netaddr import IPAddress
 from provisioningserver.ntp import config
 from provisioningserver.path import get_data_path
 from testtools.matchers import (
+    Contains,
     Equals,
     Is,
     IsInstance,
@@ -51,8 +52,10 @@ def extract_peers(configuration):
 
 
 def extract_peers_full(configuration):
+    # We expect each peer to be annotated with `xleave`, so include that
+    # in the regular expression as well.
     return re.findall(
-        r"^ *(peer) +(\S+)(?: +([^\r\n]+))?$",
+        r"^ *(peer) +(\S+) xleave(?: +([^\r\n]+))?$",
         configuration, re.MULTILINE)
 
 
@@ -269,6 +272,10 @@ class TestRenderNTPMAASConf(MAASTestCase):
             extract_tos_options(ntp_maas_conf),
             Equals([str(offset + 8), "orphan"]))
 
+    def test_configures_hwtimestamp_mode(self):
+        ntp_maas_conf = config._render_ntp_maas_conf([], [], 0)
+        self.assertThat(ntp_maas_conf, Contains("\nhwtimestamp *\n"))
+
 
 example_ntp_conf = """\
 # Welcome to the chrony configuration file. See chrony.conf(5) for more