add-managed-ntp-support (#9027)

docs/_sidebar.md

@@ -50,6 +50,7 @@
   * [DNS Stack](docs/dns-stack.md)
   * [Kubernetes reliability](docs/kubernetes-reliability.md)
   * [Local Registry](docs/kubernetes-apps/registry.md)
+  * [NTP](docs/ntp.md)
 * External Storage Provisioners
   * [RBD Provisioner](docs/kubernetes-apps/rbd_provisioner.md)
   * [CEPHFS Provisioner](docs/kubernetes-apps/cephfs_provisioner.md)

docs/ntp.md

@@ -0,0 +1,41 @@
+# NTP synchronization
+
+The Network Time Protocol (NTP) is a networking protocol for clock synchronization between computer systems. Time synchronization is important to Kubernetes and Etcd.
+
+## Enable the NTP
+
+To start the ntpd(or chrony) service and enable it at system boot. There are related specific variables:
+
+```ShellSession
+ntp_enabled: true
+```
+
+The NTP service would be enabled and sync time automatically.
+
+## Custimize the NTP configure file
+
+In the Air-Gap environment, the node cannot access the NTP server by internet. So the node can use the customized ntp server by configuring ntp file.
+
+```ShellSession
+ntp_enabled: true
+ntp_manage_config: true
+ntp_servers:
+  - "0.your-ntp-server.org iburst"
+  - "1.your-ntp-server.org iburst"
+  - "2.your-ntp-server.org iburst"
+  - "3.your-ntp-server.org iburst"
+```
+
+## Advanced Configure
+
+Enable `tinker panic` is useful when running NTP in a VM environment to avoiding clock drift on VMs. It only takes effect when ntp_manage_config is true.
+
+```ShellSession
+ntp_tinker_panic: true
+```
+
+Force sync time immediately by NTP after the ntp installed, which is useful in newly installed system.
+
+```ShellSession
+ntp_force_sync_immediately: true
+```