[hostcfgd][dns] Subscribe to DNS_NAMESERVER table to react to static …

…DNS configuration changes. (#49)

Changes are implemented according to sonic-net/SONiC#1262 HLD.
Implement unit tests for each method of DnsCfg class.

scripts/hostcfgd

@@ -1660,6 +1660,16 @@ class RSyslogCfg(object):
         self.cache['config'] = rsyslog_config
         self.cache['servers'] = rsyslog_servers
 
+
+class DnsCfg:
+
+    def load(self, *args, **kwargs):
+        self.dns_update()
+
+    def dns_update(self, *args, **kwargs):
+        run_cmd(['systemctl', 'restart', 'resolv-config'], True, False)
+
+
 class HostConfigDaemon:
     def __init__(self):
         self.state_db_conn = DBConnector(STATE_DB, 0)
@@ -1713,6 +1723,9 @@ class HostConfigDaemon:
         # Initialize RSyslogCfg
         self.rsyslogcfg = RSyslogCfg()
 
+        # Initialize DnsCfg
+        self.dnscfg = DnsCfg()
+
     def load(self, init_data):
         features = init_data['FEATURE']
         aaa = init_data['AAA']
@@ -1730,7 +1743,7 @@ class HostConfigDaemon:
         mgmt_vrf = init_data.get(swsscommon.CFG_MGMT_VRF_CONFIG_TABLE_NAME, {})
         syslog_cfg = init_data.get(swsscommon.CFG_SYSLOG_CONFIG_TABLE_NAME, {})
         syslog_srv = init_data.get(swsscommon.CFG_SYSLOG_SERVER_TABLE_NAME, {})
-
+        dns = init_data.get('DNS_NAMESERVER', {})
 
         self.feature_handler.sync_state_field(features)
         self.aaacfg.load(aaa, tacacs_global, tacacs_server, radius_global, radius_server)
@@ -1740,7 +1753,9 @@ class HostConfigDaemon:
         self.passwcfg.load(passwh)
         self.devmetacfg.load(dev_meta)
         self.mgmtifacecfg.load(mgmt_ifc, mgmt_vrf)
+
         self.rsyslogcfg.load(syslog_cfg, syslog_srv)
+        self.dnscfg.load(dns)
 
         # Update AAA with the hostname
         self.aaacfg.hostname_update(self.devmetacfg.hostname)
@@ -1856,6 +1871,10 @@ class HostConfigDaemon:
         syslog.syslog(syslog.LOG_INFO, 'SYSLOG_CONFIG table handler...')
         self.rsyslog_handler()
 
+    def dns_nameserver_handler(self, key, op, data):
+        syslog.syslog(syslog.LOG_INFO, 'DNS nameserver handler...')
+        self.dnscfg.dns_update(key, data)
+
     def wait_till_system_init_done(self):
         # No need to print the output in the log file so using the "--quiet"
         # flag
@@ -1909,6 +1928,8 @@ class HostConfigDaemon:
         self.config_db.subscribe(swsscommon.CFG_SYSLOG_SERVER_TABLE_NAME,
                                  make_callback(self.rsyslog_server_handler))
 
+        self.config_db.subscribe('DNS_NAMESERVER', make_callback(self.dns_nameserver_handler))
+
         syslog.syslog(syslog.LOG_INFO,
                       "Waiting for systemctl to finish initialization")
         self.wait_till_system_init_done()

tests/hostcfgd/hostcfgd_test.py

@@ -578,6 +578,7 @@ def test_devicemeta_event(self):
         daemon.aaacfg = mock.MagicMock()
         daemon.iptables = mock.MagicMock()
         daemon.passwcfg = mock.MagicMock()
+        daemon.dnscfg = mock.MagicMock()
         daemon.load(HOSTCFG_DAEMON_INIT_CFG_DB)
         daemon.register_callbacks()
         with mock.patch('hostcfgd.subprocess') as mocked_subprocess:
@@ -644,6 +645,7 @@ def test_mgmtiface_event(self):
         daemon.aaacfg = mock.MagicMock()
         daemon.iptables = mock.MagicMock()
         daemon.passwcfg = mock.MagicMock()
+        daemon.dnscfg = mock.MagicMock()
         daemon.load(HOSTCFG_DAEMON_INIT_CFG_DB)
         with mock.patch('hostcfgd.check_output_pipe') as mocked_check_output:
             with mock.patch('hostcfgd.subprocess') as mocked_subprocess:
@@ -670,3 +672,34 @@ def test_mgmtiface_event(self):
                     call(['cat', '/proc/net/route'], ['grep', '-E', r"eth0\s+00000000\s+[0-9A-Z]+\s+[0-9]+\s+[0-9]+\s+[0-9]+\s+202"], ['wc', '-l'])
                 ]
                 mocked_check_output.assert_has_calls(expected)
+
+    def test_dns_events(self):
+        MockConfigDb.set_config_db(HOSTCFG_DAEMON_CFG_DB)
+        MockConfigDb.event_queue = [('DNS_NAMESERVER', '1.1.1.1')]
+        daemon = hostcfgd.HostConfigDaemon()
+        daemon.register_callbacks()
+        with mock.patch('hostcfgd.run_cmd') as mocked_run_cmd:
+            try:
+                daemon.start()
+            except TimeoutError:
+                pass
+            mocked_run_cmd.assert_has_calls([call(['systemctl', 'restart', 'resolv-config'], True, False)])
+
+
+class TestDnsHandler:
+
+    @mock.patch('hostcfgd.run_cmd')
+    def test_dns_update(self, mock_run_cmd):
+        dns_cfg = hostcfgd.DnsCfg()
+        key = "1.1.1.1"
+        dns_cfg.dns_update(key, {})
+
+        mock_run_cmd.assert_has_calls([call(['systemctl', 'restart', 'resolv-config'], True, False)])
+
+    def test_load(self):
+        dns_cfg = hostcfgd.DnsCfg()
+        dns_cfg.dns_update = mock.MagicMock()
+
+        data = {}
+        dns_cfg.load(data)
+        dns_cfg.dns_update.assert_called()

tests/hostcfgd/test_vectors.py

@@ -1185,7 +1185,8 @@
     "MGMT_INTERFACE": {},
     "MGMT_VRF_CONFIG": {},
     "SYSLOG_CONFIG": {},
-    "SYSLOG_SERVER": {}
+    "SYSLOG_SERVER": {},
+    "DNS_NAMESERVER": {}
 }
 
 
@@ -1261,5 +1262,8 @@
         "vrf_global": {
             'mgmtVrfEnabled': 'true'
         }
-    }
+    },
+    "DNS_NAMESERVER": {
+        "1.1.1.1": {}
+    },
 }