[config] Adding sanity checks for config reload (sonic-net#1664)

Fixed config reload to add some system sanity checks

1) To check if the system is in running state
2) Check if the services which are grouped under delayed target up
3) Check if swss is running for at least 120 seconds
To force config reload and to avoid these checks an extra option -f/--force is added

config/main.py

@@ -701,6 +701,32 @@ def _restart_services():
     click.echo("Reloading Monit configuration ...")
     clicommon.run_command("sudo monit reload")
 
+def _get_delay_timers():
+    out = clicommon.run_command("systemctl list-dependencies sonic-delayed.target --plain |sed '1d'", return_cmd=True)
+    return [timer.strip() for timer in out.splitlines()]
+
+def _delay_timers_elapsed():
+    for timer in _get_delay_timers():
+        out = clicommon.run_command("systemctl show {} --property=LastTriggerUSecMonotonic --value".format(timer), return_cmd=True)
+        if out.strip() == "0":
+            return False
+    return True
+
+def _swss_ready():
+    out = clicommon.run_command("systemctl show swss.service --property ActiveState --value", return_cmd=True)
+    if out.strip() != "active":
+        return False
+    out = clicommon.run_command("systemctl show swss.service --property ActiveEnterTimestampMonotonic --value", return_cmd=True)
+    swss_up_time = float(out.strip())/1000000
+    now =  time.monotonic()
+    if (now - swss_up_time > 120):
+        return True
+    else:
+        return False
+
+def _system_running():
+    out = clicommon.run_command("sudo systemctl is-system-running", return_cmd=True)
+    return out.strip() == "running"
 
 def interface_is_in_vlan(vlan_member_table, interface_name):
     """ Check if an interface is in a vlan """
@@ -1190,12 +1216,26 @@ def list_checkpoints(ctx, verbose):
 @click.option('-l', '--load-sysinfo', is_flag=True, help='load system default information (mac, portmap etc) first.')
 @click.option('-n', '--no_service_restart', default=False, is_flag=True, help='Do not restart docker services')
 @click.option('-d', '--disable_arp_cache', default=False, is_flag=True, help='Do not cache ARP table before reloading (applies to dual ToR systems only)')
+@click.option('-f', '--force', default=False, is_flag=True, help='Force config reload without system checks')
 @click.argument('filename', required=False)
 @clicommon.pass_db
-def reload(db, filename, yes, load_sysinfo, no_service_restart, disable_arp_cache):
+def reload(db, filename, yes, load_sysinfo, no_service_restart, disable_arp_cache, force):
     """Clear current configuration and import a previous saved config DB dump file.
        <filename> : Names of configuration file(s) to load, separated by comma with no spaces in between
     """
+    if not force and not no_service_restart:
+        if not _system_running():
+            click.echo("System is not up. Retry later or use -f to avoid system checks")
+            return
+
+        if not _delay_timers_elapsed():
+            click.echo("Relevant services are not up. Retry later or use -f to avoid system checks")
+            return
+
+        if not _swss_ready():
+            click.echo("SwSS container is not ready. Retry later or use -f to avoid system checks")
+            return
+
     if filename is None:
         message = 'Clear current config and reload config from the default config file(s) ?'
     else: