GoでKubernetesOperatorを構築する:ステートフルアプリケーションの管理

kubebuilder init --domain mycompany.com --repo github.com/mycompany/my-operator
kubebuilder create api --group db --version v1alpha1 --kind DatabaseCluster

package v1alpha1

import (
    metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
)

// DatabaseClusterSpec defines the desired state of DatabaseCluster
type DatabaseClusterSpec struct {
    // Replicas defines the number of database nodes
    Replicas int32 `json:"replicas,omitempty"`
    
    // StorageSize defines the size of the persistent volume
    StorageSize string `json:"storageSize,omitempty"`
    
    // Image specifies the database container image
    Image string `json:"image,omitempty"`
}

// DatabaseClusterStatus defines the observed state of DatabaseCluster
type DatabaseClusterStatus struct {
    // ReadyReplicas indicates how many replicas are fully operational
    ReadyReplicas int32 `json:"readyReplicas,omitempty"`
    
    // Conditions store the current health and state of the cluster
    Conditions []metav1.Condition `json:"conditions,omitempty"`
}

//+kubebuilder:object:root=true
//+kubebuilder:subresource:status

// DatabaseCluster is the Schema for the databaseclusters API
type DatabaseCluster struct {
    metav1.TypeMeta   `json:",inline"`
    metav1.ObjectMeta `json:"metadata,omitempty"`

    Spec   DatabaseClusterSpec   `json:"spec,omitempty"`
    Status DatabaseClusterStatus `json:"status,omitempty"`
}

package controllers

import (
    "context"
    "time"

    "k8s.io/apimachinery/pkg/api/errors"
    "k8s.io/apimachinery/pkg/runtime"
    ctrl "sigs.k8s.io/controller-runtime"
    "sigs.k8s.io/controller-runtime/pkg/client"
    "sigs.k8s.io/controller-runtime/pkg/log"

    dbv1alpha1 "github.com/mycompany/my-operator/api/v1alpha1"
)

// DatabaseClusterReconciler reconciles a DatabaseCluster object
type DatabaseClusterReconciler struct {
    client.Client
    Scheme *runtime.Scheme
}

//+kubebuilder:rbac:groups=db.mycompany.com,resources=databaseclusters,verbs=get;list;watch;create;update;patch;delete
//+kubebuilder:rbac:groups=db.mycompany.com,resources=databaseclusters/status,verbs=get;update;patch
//+kubebuilder:rbac:groups=apps,resources=statefulsets,verbs=get;list;watch;create;update;patch;delete

func (r *DatabaseClusterReconciler) Reconcile(ctx context.Context, req ctrl.Request) (ctrl.Result, error) {
    logger := log.FromContext(ctx)

    // 1. Fetch the DatabaseCluster instance
    var dbCluster dbv1alpha1.DatabaseCluster
    if err := r.Get(ctx, req.NamespacedName, &dbCluster); err != nil {
        if errors.IsNotFound(err) {
            // Object not found, could have been deleted after reconcile request.
            logger.Info("DatabaseCluster resource not found. Ignoring since object must be deleted")
            return ctrl.Result{}, nil
        }
        // Error reading the object
        logger.Error(err, "Failed to get DatabaseCluster")
        return ctrl.Result{}, err
    }

    logger.Info("Reconciling DatabaseCluster", "Name", dbCluster.Name, "Replicas", dbCluster.Spec.Replicas)

    // 2. Perform Operational Logic
    // Here, you would typically:
    // - Check if a StatefulSet for this DatabaseCluster exists.
    // - If it doesn't, construct a new StatefulSet object and use r.Create() to deploy it.
    // - If it does exist, ensure its configuration (like replicas or image) matches dbCluster.Spec.
    // - Handle database-specific tasks like bootstrapping replication or taking backups.

    // Example: Update status to reflect current progress
    dbCluster.Status.ReadyReplicas = 1 // Simplified for demonstration
    if err := r.Status().Update(ctx, &dbCluster); err != nil {
        logger.Error(err, "Failed to update DatabaseCluster status")
        return ctrl.Result{}, err
    }

    // Return an empty result if successful. If you need to re-queue the request, 
    // you can return ctrl.Result{RequeueAfter: time.Minute * 1}
    return ctrl.Result{}, nil
}

// SetupWithManager sets up the controller with the Manager.
func (r *DatabaseClusterReconciler) SetupWithManager(mgr ctrl.Manager) error {
    return ctrl.NewControllerManagedBy(mgr).
        For(&dbv1alpha1.DatabaseCluster{}).
        // Owns(&appsv1.StatefulSet{}) indicates this controller manages StatefulSets created by the CRD
        Complete(r)
}