KubeSystemd

kube-systemd is a controller to help manage systemd services on each Node in clusters.

With clusters like minikube on hyberkit, which boot always from an ISO, kube-systemd could save configurations of systemd services and apply them after nodes started.

kube-systemd introduces CRD Unit to save all configurations. Users can also set a job instead. The job will restart just after each node boot.

type Unit struct {
    metav1.TypeMeta   `json:",inline"`
    metav1.ObjectMeta `json:"metadata,omitempty"`

    Spec   UnitSpec   `json:"spec,omitempty"`
    Status UnitStatus `json:"status,omitempty"`
}

type UnitSpec struct {
	// INSERT ADDITIONAL SPEC FIELDS - desired state of cluster
	// Important: Run "make" to regenerate code after modifying this file

	// Specify an existed job which will restart once node boots up.
	// +optional
	Job corev1.ObjectReference `json:"job,omitempty"`

	// Defines a systemd unit.
	// +optional
	HostUnit HostSystemdUnit `json:"unit,omitempty"`
}

type HostSystemdUnit struct {
	// Path defines the absolute path on the host of the unit.
	Path string `json:"path,omitempty"`

	// Definition specifies the unit definition. If set, it is written to the unit configuration which Path defines.
	// Or, the original unit on the host will be used.
	// +optional
	Definition string `json:"definition,omitempty"`

	// Config specifies config files and contents on the host with respect to the systemd unit.
	// The key is the absolute path of the configuration file. And, the value is the file content.
	// +optional
	Config map[string]string `json:"config,omitempty"`
}

Install

kubectl apply -f https://raw.githubusercontent.com/warm-metal/kube-systemd/master/config/samples/install.yaml

Demo

We can create a unit to modify NTP server configuration in a minikube cluster to make sure the cluster clock is always synchronized to the NTP server.

apiVersion: core.systemd.warmmetal.tech/v1
kind: Unit
metadata:
  name: systemd-timesyncd.service
spec:
  unit:
    path: "/lib/systemd/system/systemd-timesyncd.service"
    config:
      "/etc/systemd/timesyncd.conf": |
        [Time]
        NTP=ntp1.aliyun.com
---
apiVersion: core.systemd.warmmetal.tech/v1
kind: Unit
metadata:
  name: binfmt-register
spec:
  job:
    kind: Job
    name: binfmt-register
    namespace: default

After the unit executed, we could see that its status changed. That is, status.execTimestamp is updated to the time last executed. If errors raised, the status.error would be also updated.

apiVersion: core.systemd.warmmetal.tech/v1
kind: Unit
metadata:
  annotations:
    kubectl.kubernetes.io/last-applied-configuration: |
      {"apiVersion":"core.systemd.warmmetal.tech/v1","kind":"Unit","metadata":{"annotations":{},"name":"systemd-timesyncd.service"},"spec":{"unit":{"config":{"/etc/systemd/timesyncd.conf":"[Time]\nNTP=ntp1.aliyun.com\n"},"path":"/lib/systemd/system/systemd-timesyncd.service"}}}
  creationTimestamp: "2021-06-05T14:20:31Z"
  generation: 3
  name: systemd-timesyncd.service
  resourceVersion: "1179328"
  uid: f150a842-9804-4313-8f72-99ad3151cf46
spec:
  unit:
    config:
      /etc/systemd/timesyncd.conf: |
        [Time]
        NTP=ntp1.aliyun.com
    path: /lib/systemd/system/systemd-timesyncd.service
status:
  execTimestamp: "2021-06-05T14:23:43Z"