Controller Manager Components in Kubernetes

1. Overview

The Controller Manager in Kubernetes is a control plane component that manages controllers. Each controller watches the state of your cluster and makes or requests changes where needed. This lesson will explore the various components of the Controller Manager, their roles, and best practices for managing them.

2. Key Components

2.3 Controller Manager

The Controller Manager is responsible for managing various controllers. It runs as a single process but can manage multiple controllers, ensuring that they can communicate and share resources effectively.

3. Functionality

The Controller Manager performs the following key functions:

1. Monitoring the state of the cluster.
2. Managing the lifecycle of various resources.
3. Responding to changes in the cluster's state.

3.1 Example of a Controller

Here’s a basic example of a custom controller written in Go:

package main

import (
    "context"
    "log"
    "sigs.k8s.io/controller-runtime/pkg/controller"
    "sigs.k8s.io/controller-runtime/pkg/controller/controllerutil"
    "sigs.k8s.io/controller-runtime/pkg/handler"
    "sigs.k8s.io/controller-runtime/pkg/manager"
    "sigs.k8s.io/controller-runtime/pkg/source"
)

func main() {
    ctx := context.Background()
    mgr, err := manager.New(config.GetConfigOrDie(), manager.Options{})
    if err != nil {
        log.Fatalf("unable to set up overall controller manager: %v", err)
    }

    c, err := controller.New("my-controller", mgr, controller.Options{})
    if err != nil {
        log.Fatalf("unable to create controller: %v", err)
    }

    err = c.Watch(&source.Kind{Type: &v1.Pod{}}, &handler.EnqueueRequestForObject{})
    if err != nil {
        log.Fatalf("unable to watch pods: %v", err)
    }

    if err := mgr.Start(ctx); err != nil {
        log.Fatalf("unable to start manager: %v", err)
    }
}
            

4. Best Practices

• Implement logging and monitoring for the Controller Manager.
• Use leader election to ensure only one Controller Manager is active at a time.
• Regularly update and maintain the Controller Manager for optimal security and performance.

5. FAQ