Kubernetes write custom controller

Original link: Kubernetes write custom controller

Kubernetes official from github of a map:

 

 

As shown in the figure is divided into components in FIG client-go and custom controller two parts:

1. client-go section

   • Reflector: monitor a specific resource k8s api, the new object into the monitored Delta Fifo queue, this function is completed ListAndWatch.
   • Informer: Delta Fifo out objects from the queue, the function of this operation is complete processLoop.
   • Indexer: provides thread-level security to store objects and key.

2. custom-controller portion

   • Informer reference: Informer object reference
   • Indexer reference: Indexer object reference
   • Resource Event Handlers: callback function is called the Informer, the role of these functions are used to get the object key, and the key into the Work queue, in order to do further processing.
   • Work queue: work queue, the processing for separating objects delivered thereto, to prepare Resource event handler functions to extract key object passed and added to the work queue.
   • Process Item: Work queue for processing in the object, there may be processed together with one or more other functions; These functions typically use Indexer reference Listing wrapper or to retrieve the object corresponding to the key.

The official code examples client-go

package main

import (
    "flag"
    "fmt"
    "time"

    "k8s.io/klog"

    "k8s.io/api/core/v1"
    meta_v1 "k8s.io/apimachinery/pkg/apis/meta/v1"
    "k8s.io/apimachinery/pkg/fields"
    "k8s.io/apimachinery/pkg/util/runtime"
    "k8s.io/apimachinery/pkg/util/wait"
    "k8s.io/client-go/kubernetes"
    "k8s.io/client-go/tools/cache"
    "k8s.io/client-go/tools/clientcmd"
    "k8s.io/client-go/util/workqueue " 
) 

// definition of a structure the Controller 
type the Controller struct { 
    Indexer cache.Indexer 
    Queue workqueue.RateLimitingInterface 
    Informer cache.Controller 
} 

// Get controller function 
func NewController (queue workqueue.RateLimitingInterface , Indexer cache.Indexer, Informer cache.Controller) * the Controller {
     return & the Controller { 
        Informer: Informer, 
        Indexer: Indexer, 
        Queue: Queue, 
    } 
} 

// processed workqueue in 
func (c * Controller) processNextItem ( )bool {
    // Wait until there is a new item in the working queue
    key, quit := c.queue.Get()
    if quit {
        return false
    }
    // Tell the queue that we are done with processing this key. This unblocks the key for other workers
    // This allows safe parallel processing because two pods with the same key are never processed in
    // parallel.
    defer c.queue.Done(key)

    // Invoke the method containing the business logic
    err := c.syncToStdout(key.(string))
    // Handle the error if something went wrong during the execution of the business logic
    c.handleErr(err, key)
    return true
}

// syncToStdout is the business logic of the controller. In this controller it simply prints
// information about the pod to stdout. In case an error happened, it has to simply return the error.
// The retry logic should not be part of the business logic.
func (c *Controller) syncToStdout(key string) error {
    obj, exists, err := c.indexer.GetByKey(key)
    if err != nil {         klog.Errorf("Fetching object with key %s from store failed with %v", key, err)
        return err
    }

    if !exists {         // Below we will warm up our cache with a Pod, so that we will see a delete for one pod
        fmt.Printf("Pod %s does not exist anymore\n", key)
    } else {
        // Note that you also have to check the uid if you have a local controlled resource, which
        // is dependent on the actual instance, to detect that a Pod was recreated with the same name
        fmt.Printf("Sync/Add/Update for Pod %s\n", obj.(*v1.Pod).GetName())
    }
    return nil
}

// handleErr checks if an error happened and makes sure we will retry later.
func (c *Controller) handleErr(err error, key interface{}) {
    if err == nil {
        // Forget about the #AddRateLimited history of the key on every successful synchronization.
        // This ensures that future processing of updates for this key is not delayed because of
        // an outdated error history.
        c.queue.Forget(key)
        return
    }

    // This controller retries 5 times if something goes wrong. After that, it stops trying.
    if c.queue.NumRequeues(key) < 5 {
        klog.Infof("Error syncing pod %v: %v", key, err)

        // Re-enqueue the key rate limited. Based on the rate limiter on the
        // queue and the re-enqueue history, the key will be processed later again.
        c.queue.AddRateLimited(key)
        return
    }

    c.queue.Forget(key)
    // Report to an external entity that, even after several retries, we could not successfully process this key
    runtime.HandleError(err)
    klog.Infof("Dropping pod %q out of the queue: %v", key, err)
}

func (c *Controller) Run(threadiness int, stopCh chan struct{}) {
    defer runtime.HandleCrash()

    // Let the workers stop when we are done
    defer c.queue.ShutDown()
    klog.Info("Starting Pod controller")

    go c.informer.Run(stopCh)

    // Wait for all involved caches to be synced, before processing items from the queue is started
    if !cache.WaitForCacheSync(stopCh, c.informer.HasSynced) {         runtime.HandleError(fmt.Errorf("Timed out waiting for caches to sync"))
        return
    }

    for i := 0; i < threadiness; i++ {
        go wait.Until(c.runWorker, time.Second, stopCh)
    }

    <-stopCh
    klog.Info("Stopping Pod controller")
}

func (c *Controller) runWorker() {
    for c.processNextItem() {
    }
}

func main() {
    var kubeconfig string
    var master string

    // 指定kubeconfig文件
    flag.StringVar(&kubeconfig, "kubeconfig", "", "absolute path to the kubeconfig file")
    flag.StringVar(&master, "master", "", "master url")
    flag.Parse()

    // creates the connection
    config, err := clientcmd.BuildConfigFromFlags(master, kubeconfig)
    if err != nil {         klog.Fatal(err)
    }

    // creates the clientset
    clientset, err := kubernetes.NewForConfig(config)
    if err != nil {         klog.Fatal(err)
    }

    // create the pod watcher
    podListWatcher := cache.NewListWatchFromClient(clientset.CoreV1().RESTClient(), "pods", v1.NamespaceDefault, fields.Everything())

    // create the workqueue
    queue := workqueue.NewRateLimitingQueue(workqueue.DefaultControllerRateLimiter())

    // Bind the workqueue to a cache with the help of an informer. This way we make sure that
    // whenever the cache is updated, the pod key is added to the workqueue.
    // Note that when we finally process the item from the workqueue, we might see a newer version
    // of the Pod than the version which was responsible for triggering the update.
    indexer, informer := cache.NewIndexerInformer(podListWatcher, &v1.Pod{}, 0, cache.ResourceEventHandlerFuncs{
        AddFunc: func(obj interface{}) {
            key, err := cache.MetaNamespaceKeyFunc(obj)
            if err == nil {
                queue.Add(key)
            }
        },
        UpdateFunc: func(old interface{}, new interface{}) {
            key, err := cache.MetaNamespaceKeyFunc(new)
            if err == nil {
                queue.Add(key)
            }
        },
        DeleteFunc: func(obj interface{}) {
            // IndexerInformer uses a delta queue, therefore for deletes we have to use this
            // key function.
            key, err := cache.DeletionHandlingMetaNamespaceKeyFunc(obj)
            if err == nil {
                queue.Add(key)
            }
        },
    }, cache.Indexers{})

    controller := NewController(queue, indexer, informer)

    // We can now warm up the cache for initial synchronization.
    // Let's suppose that we knew about a pod "mypod" on our last run, therefore add it to the cache. // If this pod is not there anymore, the controller will be notified about the removal after the // cache has synchronized. indexer.Add(&v1.Pod{ ObjectMeta: meta_v1.ObjectMeta{ Name: "mypod", Namespace: v1.NamespaceDefault, }, }) // Now let's start the controller
    stop := make(chan struct{})
    defer close(stop)
    go controller.Run(1, stop)

    // Wait forever
    select {}
}