#Managing Node Configuration with MachineConfig

You can use the tasks described in this section to create MachineConfig objects that modify files, systemd units, and SSH public keys on nodes, as well as to recover nodes that have experienced configuration drift.

MachineConfig supports Ignition specification version 3.4. All MachineConfig objects must be created in compliance with this version.

In certain situations, the configuration on a node may not fully match the configuration currently applied through the MachineConfig. This condition is referred to as configuration drift. The machine configuration daemon periodically verifies whether a node's configuration has drifted. If drift is detected, the node is marked as Degraded and remains in that state until an administrator restores the expected configuration.

The following examples demonstrate how to use MachineConfig objects to manage node configurations.

#Configuring the Chrony Time Service

To configure the Chrony time synchronization service (chronyd) and specify the NTP servers and related settings, you can update the chrony.conf file on the target nodes via a MachineConfig object.

1. First, create a temporary file that contains the desired Chrony configuration:

   chrony.conf
   server 0.centos.pool.ntp.org iburst
   server 1.centos.pool.ntp.org iburst
   makestep 1.0 3
   rtcsync
   logdir /var/log/chrony

2. Then, base64-encode the contents of the file:

   base64 -w0 chrony.conf

3. Create a MachineConfig object named 99-worker-chrony. In the .spec.config.storage.files[0].contents.source field, insert the base64-encoded string in the format data:text/plain;base64,<encoded-content>:

   apiVersion: machineconfiguration.alauda.io/v1alpha1
   kind: MachineConfig
   metadata:
     name: 99-worker-chrony
     labels:
       machineconfiguration.alauda.io/role: worker
   spec:
     config:
       ignition:
         version: 3.4.0
       storage:
         files:
           - path: /etc/chrony.conf
             mode: 0644
             contents:
               source: 'data:text/plain;base64,c2VydmVyIDAuY2VudG9zLnBvb2wubnRwLm9yZyBpYnVyc3QKc2VydmVyIDEuY2VudG9zLnBvb2wubnRwLm9yZyBpYnVyc3QKbWFrZXN0ZXAgMS4wIDMKcnRjc3luYwpsb2dkaXIgL3Zhci9sb2cvY2hyb255Cg=='

   This configuration creates a MachineConfig object that applies a customized chrony.conf file to nodes associated with the worker machine configuration pool. The file will be written to /etc/chrony.conf on each node, with file permissions set to 0644.

#Disabling the Chrony Time Service

To disable the Chrony time synchronization service on nodes with a specific role, you can create a MachineConfig object that overrides the systemd unit definition and disables the service.

Example configuration:

apiVersion: machineconfiguration.alauda.io/v1alpha1
kind: MachineConfig
metadata:
  name: 99-worker-disable-chrony
  labels:
    machineconfiguration.alauda.io/role: worker
spec:
  config:
    ignition:
      version: 3.4.0
    systemd:
      units:
        - name: chronyd.service
          enabled: false
          contents: |
            [Unit]
            Description=NTP client/server
            Documentation=man:chronyd(8) man:chrony.conf(5)
            After=ntpdate.service sntp.service ntpd.service
            Conflicts=ntpd.service systemd-timesyncd.service
            ConditionCapability=CAP_SYS_TIME

            [Service]
            Type=forking
            PIDFile=/run/chrony/chronyd.pid
            EnvironmentFile=-/etc/sysconfig/chronyd
            ExecStart=/usr/sbin/chronyd $OPTIONS
            ExecStartPost=/usr/libexec/chrony-helper update-daemon
            PrivateTmp=yes
            ProtectHome=yes
            ProtectSystem=full

            [Install]
            WantedBy=multi-user.target

This configuration pushes a custom version of the chronyd.service unit file to the nodes in the worker machine configuration pool. The service is explicitly disabled. Once the configuration is applied and the nodes are rebooted, the Chrony service will no longer start automatically.

#Configuring the SSH Public Key for the boot User

The machine configuration system allows you to configure an SSH public key for the boot user on managed nodes. Configuration for other user accounts is not supported. Note that machine configuration will not create users or groups automatically—you must ensure that the boot user and group exist on the node before applying the configuration.

Example configuration:

apiVersion: machineconfiguration.alauda.io/v1alpha1
kind: MachineConfig
metadata:
  name: 99-worker-ssh
  labels:
    machineconfiguration.alauda.io/role: worker
spec:
  config:
    ignition:
      version: 3.4.0
    passwd:
      users:
        - user: boot
          sshAuthorizedKeys:
            - ssh-rsa <ssh-public-key>

This MachineConfig will install the specified SSH key in the /home/boot/.ssh/authorized_keys file on nodes in the worker machine configuration pool.

#Recovering from Configuration Drift

If a node's configuration diverges from its assigned MachineConfig, it will be marked as Degraded. In this state, the node continues to operate but cannot receive further configuration updates until the issue is resolved.

There are two ways to restore a node from this degraded state:

1. Manually revert the configuration You can manually adjust the files and permissions on the node to exactly match those specified in the assigned MachineConfig. The system will detect the correction and clear the degraded status.

2. Force the configuration to be reapplied Create an empty file at /run/machine-config-daemon-force on the affected node. The machine configuration daemon will detect this trigger, reapply the current MachineConfig, delete the trigger file, and reboot the node. After rebooting, the node will transition from Degraded back to Done.