cc_ntp: fallback on timesyncd configuration if ntp is not installable

Some systems like Ubuntu-Core do not provide an ntp package for
installation but do include systemd-timesyncd (an ntp client).
On such systems cloud-init will generate a timesyncd configuration
using the 'servers' and 'pools' values as ntp hosts for timesyncd to use.

LP: #1686485

1 files changed, 45 insertions, 13 deletions

diff --git a/cloudinit/config/cc_ntp.py b/cloudinit/config/cc_ntp.py
index 31ed64e3..a02b4bf1 100644
--- a/cloudinit/config/cc_ntp.py
+++ b/cloudinit/config/cc_ntp.py
@@ -50,6 +50,7 @@ LOG = logging.getLogger(__name__)
 
 frequency = PER_INSTANCE
 NTP_CONF = '/etc/ntp.conf'
+TIMESYNCD_CONF = '/etc/systemd/timesyncd.conf.d/cloud-init.conf'
 NR_POOL_SERVERS = 4
 distros = ['centos', 'debian', 'fedora', 'opensuse', 'ubuntu']
 
@@ -132,20 +133,50 @@ def handle(name, cfg, cloud, log, _args):
                             " is a %s %instead"), type_utils.obj_name(ntp_cfg))
 
     validate_cloudconfig_schema(cfg, schema)
+    if ntp_installable():
+        service_name = 'ntp'
+        confpath = NTP_CONF
+        template_name = None
+        packages = ['ntp']
+        check_exe = 'ntpd'
+    else:
+        service_name = 'systemd-timesyncd'
+        confpath = TIMESYNCD_CONF
+        template_name = 'timesyncd.conf'
+        packages = []
+        check_exe = '/lib/systemd/systemd-timesyncd'
+
     rename_ntp_conf()
     # ensure when ntp is installed it has a configuration file
     # to use instead of starting up with packaged defaults
-    write_ntp_config_template(ntp_cfg, cloud)
-    install_ntp(cloud.distro.install_packages, packages=['ntp'],
-                check_exe="ntpd")
-    # if ntp was already installed, it may not have started
+    write_ntp_config_template(ntp_cfg, cloud, confpath, template=template_name)
+    install_ntp(cloud.distro.install_packages, packages=packages,
+                check_exe=check_exe)
+
     try:
-        reload_ntp(systemd=cloud.distro.uses_systemd())
+        reload_ntp(service_name, systemd=cloud.distro.uses_systemd())
     except util.ProcessExecutionError as e:
         LOG.exception("Failed to reload/start ntp service: %s", e)
         raise
 
 
+def ntp_installable():
+    """Check if we can install ntp package
+
+    Ubuntu-Core systems do not have an ntp package available, so
+    we always return False.  Other systems require package managers to install
+    the ntp package If we fail to find one of the package managers, then we
+    cannot install ntp.
+    """
+    if util.system_is_snappy():
+        return False
+
+    if any(map(util.which, ['apt-get', 'dnf', 'yum', 'zypper'])):
+        return True
+
+    return False
+
+
 def install_ntp(install_func, packages=None, check_exe="ntpd"):
     if util.which(check_exe):
         return
@@ -156,7 +187,7 @@ def install_ntp(install_func, packages=None, check_exe="ntpd"):
 
 
 def rename_ntp_conf(config=None):
-    """Rename any existing ntp.conf file and render from template"""
+    """Rename any existing ntp.conf file"""
     if config is None:  # For testing
         config = NTP_CONF
     if os.path.exists(config):
@@ -171,7 +202,7 @@ def generate_server_names(distro):
     return names
 
 
-def write_ntp_config_template(cfg, cloud):
+def write_ntp_config_template(cfg, cloud, path, template=None):
     servers = cfg.get('servers', [])
     pools = cfg.get('pools', [])
 
@@ -185,19 +216,20 @@ def write_ntp_config_template(cfg, cloud):
         'pools': pools,
     }
 
-    template_fn = cloud.get_template_filename('ntp.conf.%s' %
-                                              (cloud.distro.name))
+    if template is None:
+        template = 'ntp.conf.%s' % cloud.distro.name
+
+    template_fn = cloud.get_template_filename(template)
     if not template_fn:
         template_fn = cloud.get_template_filename('ntp.conf')
         if not template_fn:
             raise RuntimeError(("No template found, "
-                                "not rendering %s"), NTP_CONF)
+                                "not rendering %s"), path)
 
-    templater.render_to_file(template_fn, NTP_CONF, params)
+    templater.render_to_file(template_fn, path, params)
 
 
-def reload_ntp(systemd=False):
-    service = 'ntp'
+def reload_ntp(service, systemd=False):
     if systemd:
         cmd = ['systemctl', 'reload-or-restart', service]
     else: