NTP
"""

Schéma de base
''''''''''''''

.. graphviz::

   digraph "arch" {
    nodesep=0.9;
    ranksep=1.7;
    subgraph cluster_NTP1 {
        label = "Top Hypervisor #1";
        "server1"[label="ntp"];
    }
    subgraph cluster_NTP2 {
        label = "Top Hypervisor #2";
        "server2"[label="ntp"];
    }
    subgraph cluster_NTP3 {
        label = "Top Hypervisor #3";
        "server3"[label="ntp"];
    }
    subgraph cluster_worker1_NTP {
        label = "Worker Hypervisor #1";
        "client1"[label="ntp"];
      subgraph cluster_NTP4 {
          label = "VM";
          "server4"[label="ntp"];
      }
    }

    subgraph cluster_worker2_NTP {
        label = "Worker Hypervisor #N";
        "client2"[label="ntp"];
      subgraph cluster_NTP5 {
          label = "VM";
          "server5"[label="ntp"];
      }
    }

    subgraph cluster_islet1_NTP {
        label = "Islet Hypervisor #I";
        "client3"[label="ntp"];
    }

    subgraph cluster_compute1 {
        label = "Compute node #1";
        "compute1"[label="ntp"];
    }
    subgraph cluster_compute2 {
        label = "Compute node #2";
        "compute2"[label="ntp"];
    }
    subgraph cluster_compute3 {
        label = "Compute node #n";
        "compute3"[label="ntp"];
    }

    "upstream"[label="upstream ntp\nserver", style="dotted"];

    "compute1" -> "server4"[color=blue];
    "compute1" -> "server5"[color=blue];
    "compute2" -> "server4"[color=blue];
    "compute2" -> "server5"[color=blue];
    "compute3" -> "server4"[color=blue];
    "compute3" -> "server5"[color=blue];
    "server5" -> "server3"[color=red];
    "server5" -> "server2"[color=red];
    "server5" -> "server1"[color=red];
    "server4" -> "server3"[color=red];
    "server4" -> "server2"[color=red];
    "server4" -> "server1"[color=red];
    "client1" -> "server3"[color=blue];
    "client1" -> "server2"[color=blue];
    "client1" -> "server1"[color=blue];
    "client2" -> "server3"[color=blue];
    "client2" -> "server2"[color=blue];
    "client2" -> "server1"[color=blue];
    "client3" -> "server3"[color=blue];
    "client3" -> "server2"[color=blue];
    "client3" -> "server1"[color=blue];
    "server3" -> "upstream"[color=red];
    "server2" -> "upstream"[color=red];
    "server1" -> "upstream"[color=red];

  { rank = sink;
    Legend [shape=none, margin=0, label=<
    <TABLE BORDER="0" CELLBORDER="1" CELLSPACING="0" CELLPADDING="4">
     <TR>
      <TD COLSPAN="2"><B>Legend</B></TD>
     </TR>
     <TR>
      <TD>Client sync</TD>
      <TD BGCOLOR="BLUE"></TD>
     </TR>
     <TR>
      <TD>Server sync</TD>
      <TD BGCOLOR="RED"></TD>
     </TR>
    </TABLE>
   >];
  }
   }


Description
'''''''''''

L'architecture NTP d'Ocean doit avoir au moins 3 services configurés en 'peer' pour être le plus précis possible.
Ces trois services seront hébergés sur les Top Hyperviseurs.
Ces trois hyperviseurs pourront être synchronisés avec une source externe au calculateur.

Tous les Workers hyperviseurs ainsi que toutes les VMs sont client(e)s du service NTP des Top.

Le démon ntpd est utilisé sous RedHat/CentOS 7.  Il est remplacé par chronyd sous RedHat/CentOS 8.

..
   Le service NTP sera colocalisé sur les VMs DNS en master et DHCP pour le slave.

..
   Si le matériel le permet, ont utilisera les switchs synchronisés sur les 3 top hyperviseurs.

..
       NTP EXT
         |
     ----------
     '    '   '
    TOP  TOP TOP   ----------.
     '----'---'              |
         |                   '--- VMs --- Clients
       WORKER

..
    Le démon ntpd n'est plus disponible en RedHat 8. Seul le démon chronyd est implémenté par RedHat.

.. raw:: latex

  \clearpage