Introduction

In a regular OpenShift environment, NTP server is more less like this:

In a self-contained cluster with no connection to external networks NTP server is not reachable, but a reachable NTP server is required for proper cluster synchronization. Cluster does use SSL certificates that require validation and might fail if the dates between the systems are not in sync or at least pretty close in time.

We’ve several components already available in our OpenShift cluster that are very useful:

  • MCO allows to define configuration to be applied by role, etc to the nodes
  • chrony is the client/server installed in Red Hat CoreOS images for connecting to an external NTP Server
  • chrony is already being used and configured via MachineConfigs to point to the configured NTP servers.

Via a MCO change with a higher number than the prior ones, we can override the chrony.conf file by role, so that masters can set up required steps to serve time to other machines in the network even with external access to upstream servers or local GPS devices.

Workers can point to the masters so that those can be in sync via another file or via setting the proper install-config.yaml settings at install time.

There are some risks without a proper time sync:

  • Systems might be not synced with real clock at all because of no external NTP access and no local time generator attached (like a GPS device).
  • Users might forget to define proper BIOS time on all the systems prior to installation.

In regards to system supportability, as applying MCO changes to the cluster and configuring chrony.conf is documented already it should not have a heavy impact on the cluster supportability (check references).

Implementation

First we need an available cluster installed, and remember:

  • Define proper clock/date in each system’s BIOS settings or installation will fail.

In order to configure the ntp server, we’ll make use of the master servers, but we also need to deal with:

To allow multiple servers in the network to use the same local configuration and to be synchronized to one another, without confusing clients that poll more than one server, use the orphan option of the local directive which enables the orphan mode. Each server needs to be configured to poll all other servers with local. This ensures that only the server with the smallest reference ID has the local reference active and other servers are synchronized to it. When the server fails, another one will take over.

In order to do so, define a sample chrony.conf file:

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# Use public servers from the pool.ntp.org project.
# Please consider joining the pool (https://www.pool.ntp.org/join.html).

# This file is managed by the machine config operator
server master-0.cloud iburst
server master-1.cloud iburst
server master-2.cloud iburst

stratumweight 0
driftfile /var/lib/chrony/drift
rtcsync
makestep 10 3
bindcmdaddress 127.0.0.1
bindcmdaddress ::1
keyfile /etc/chrony.keys
commandkey 1
generatecommandkey
noclientlog
logchange 0.5
logdir /var/log/chrony

# Serve as local NTP server for all clients even if we're not in sync with upstream:

# Allow NTP client access from local network.
allow all
# Serve time even if not synchronized to a time source.
local stratum 3 orphan

This file is similar to the standard one but with the added directives at the end to allow all clients to sync time against this and set the local stratum to level 3, so that others can sync from this server.

Additionally the orphan option does the following:

This option enables a special orphan mode, where sources with stratum equal to the local stratum are assumed to not serve real time. They are ignored unless no other source is selectable and their reference IDs are smaller than the local reference ID.

This allows multiple servers in the network to use the same local configuration and to be synchronised to one another, without confusing clients that poll more than one server. Each server needs to be configured to poll all other servers with the local directive. This ensures only the server with the smallest reference ID has the local reference active and others are synchronised to it. When that server fails, another will take over.

In the case of the worker nodes, we just point to the master servers in our cluster via a sample chrony.conf file:

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# This file is managed by the machine config operator
server master-0.cloud iburst
server master-1.cloud iburst
server master-2.cloud iburst

stratumweight 0
driftfile /var/lib/chrony/drift
rtcsync
makestep 10 3
bindcmdaddress 127.0.0.1
bindcmdaddress ::1
keyfile /etc/chrony.keys
commandkey 1
generatecommandkey
noclientlog
logchange 0.5
logdir /var/log/chrony

Applying the configuration changes

We can later configure prior chrony.conf via a yaml applied to our cluster.

For the master nodes:

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# This example MachineConfig replaces /etc/chrony.conf
apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfig
metadata:
  labels:
    machineconfiguration.openshift.io/role: master
  name: 99-master-etc-chrony-conf-override-to-server
spec:
  config:
    ignition:
      version: 2.2.0
    storage:
      files:
        - contents:
            source: data:text/plain;charset=utf-8;base64,BASE64ENCODEDCONFIGFILE
          filesystem: root
          mode: 0644
          path: /etc/chrony.conf

And then apply it:

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[[email protected] ~]$ oc apply -f ntp-server.yaml
machineconfig.machineconfiguration.openshift.io/99-master-etc-chrony-conf-override-for-server created

And for the workers:

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# This example MachineConfig replaces /etc/chrony.conf
apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfig
metadata:
  labels:
    machineconfiguration.openshift.io/role: worker
  name: 99-master-etc-chrony-conf-override-for-worker
spec:
  config:
    ignition:
      version: 2.2.0
    storage:
      files:
        - contents:
            source: data:text/plain;charset=utf-8;base64,BASE64ENCODEDCONFIGFILE
          filesystem: root
          mode: 0644
          path: /etc/chrony.conf

And apply in a similar way to master:

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[[email protected] ~]$ oc apply -f ntp-client.yaml
machineconfig.machineconfiguration.openshift.io/99-master-etc-chrony-conf-override-for-worker created

Validating

Once the above (or equivalent) file is applied for both master and workers, we can execute oc describe machineconfigpool to check the status of the applied overrides.

And for final validation, checking:

  • cat /etc/chrony.conf on the nodes to validate the override we applied.
  • chronyc sources will list the defined clock sources for each system

References

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Pablo Iranzo Gómez Avatar Pablo Iranzo Gómez opensource enthusiast and Lego fan doing some python simple programs like @redken_bot in telegram, etc
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