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Configmap/Secret Manager

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Configmap/Secret Manager

Kubernetes Source Code Reading

Abser·Ari
·Jun 25, 2022·

6 min read

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Table of contents

  • ReadLink
  • Configmap Manager
  • Secret Manager
  • cache_based_manager
  • watch_based_manager

Configmap Manager

// Manager interface provides methods for Kubelet to manage ConfigMap.
type Manager interface {
    // Get configmap by configmap namespace and name.
    GetConfigMap(namespace, name string) (*v1.ConfigMap, error)

    // WARNING: Register/UnregisterPod functions should be efficient,
    // i.e. should not block on network operations.

    // RegisterPod registers all configmaps from a given pod.
    RegisterPod(pod *v1.Pod)

    // UnregisterPod unregisters configmaps from a given pod that are not
    // used by any other registered pod.
    UnregisterPod(pod *v1.Pod)
}

接口非常简单。

  1. GetConfigMap : 通过 namespace 和 name 获取对应 ConfigMap 对象。
  2. RegisterPod(pod *v1.Pod):把指定 Pod 对象 yaml 指定的 configmap 注册到 Controller 中管理
  3. UnregisterPod(pod *v1.Pod):把指定 Pod 对象 yaml 指定的 configmap 从 Controller 中注册管理中删除,注意 ConfigMap 需要没有任何其他已注册的 Pod 引用(即无被依赖项)才可以删除

当前代码中有两种 manager 的实现

-NewCachingConfigMapManager(kubeClient clientset.Interface, getTTL manager.GetObjectTTLFunc) Manager:该实现有两点逻辑

  • 当一个 Pod 创建或者更新时,所有的 configmap 缓存都失效。
  • GetObject() 调用首先从本地缓存获取,失败则访问 APISever 并刷新 configmap 的缓存。
// NewCachingConfigMapManager creates a manager that keeps a cache of all configmaps
// necessary for registered pods.
// It implement the following logic:
// - whenever a pod is create or updated, the cached versions of all configmaps
//   are invalidated
// - every GetObject() call tries to fetch the value from local cache; if it is
//   not there, invalidated or too old, we fetch it from apiserver and refresh the
//   value in cache; otherwise it is just fetched from cache
func NewCachingConfigMapManager(kubeClient clientset.Interface, getTTL manager.GetObjectTTLFunc) Manager {
    getConfigMap := func(namespace, name string, opts metav1.GetOptions) (runtime.Object, error) {
        return kubeClient.CoreV1().ConfigMaps(namespace).Get(context.TODO(), name, opts)
    }
    configMapStore := manager.NewObjectStore(getConfigMap, clock.RealClock{}, getTTL, defaultTTL)
    return &configMapManager{
        manager: manager.NewCacheBasedManager(configMapStore, getConfigMapNames),
    }
}
  • NewWatchingConfigMapManager(kubeClient clientset.Interface, resyncInterval time.Duration) Manager
    • 当一个 Pod 创建或者更新时,会对指定该 Pod 引用的资源,并且该资源未被其他 Pod 引用进行独立的 watch。
    • GetObject() 调用首先从本地缓存获取
// NewWatchingConfigMapManager creates a manager that keeps a cache of all configmaps
// necessary for registered pods.
// It implements the following logic:
// - whenever a pod is created or updated, we start individual watches for all
//   referenced objects that aren't referenced from other registered pods
// - every GetObject() returns a value from local cache propagated via watches
func NewWatchingConfigMapManager(kubeClient clientset.Interface, resyncInterval time.Duration) Manager {
    listConfigMap := func(namespace string, opts metav1.ListOptions) (runtime.Object, error) {
        return kubeClient.CoreV1().ConfigMaps(namespace).List(context.TODO(), opts)
    }
    watchConfigMap := func(namespace string, opts metav1.ListOptions) (watch.Interface, error) {
        return kubeClient.CoreV1().ConfigMaps(namespace).Watch(context.TODO(), opts)
    }
    newConfigMap := func() runtime.Object {
        return &v1.ConfigMap{}
    }
    isImmutable := func(object runtime.Object) bool {
        if configMap, ok := object.(*v1.ConfigMap); ok {
            return configMap.Immutable != nil && *configMap.Immutable
        }
        return false
    }
    gr := corev1.Resource("configmap")
    return &configMapManager{
        manager: manager.NewWatchBasedManager(listConfigMap, watchConfigMap, newConfigMap, isImmutable, gr, resyncInterval, getConfigMapNames),
    }
}

Secret Manager

secret manager 除了资源类型和 configmap 不一样,其他逻辑相同,所以仅列出两种 secret manager 的初始化函数。
/pkg /kubelet /secret /secret_manager.go

// NewCachingSecretManager creates a manager that keeps a cache of all secrets
// necessary for registered pods.
// It implements the following logic:
// - whenever a pod is created or updated, the cached versions of all secrets
//   are invalidated
// - every GetObject() call tries to fetch the value from local cache; if it is
//   not there, invalidated or too old, we fetch it from apiserver and refresh the
//   value in cache; otherwise it is just fetched from cache
func NewCachingSecretManager(kubeClient clientset.Interface, getTTL manager.GetObjectTTLFunc) Manager {
    getSecret := func(namespace, name string, opts metav1.GetOptions) (runtime.Object, error) {
        return kubeClient.CoreV1().Secrets(namespace).Get(context.TODO(), name, opts)
    }
    secretStore := manager.NewObjectStore(getSecret, clock.RealClock{}, getTTL, defaultTTL)
    return &secretManager{
        manager: manager.NewCacheBasedManager(secretStore, getSecretNames),
    }
}

// NewWatchingSecretManager creates a manager that keeps a cache of all secrets
// necessary for registered pods.
// It implements the following logic:
// - whenever a pod is created or updated, we start individual watches for all
//   referenced objects that aren't referenced from other registered pods
// - every GetObject() returns a value from local cache propagated via watches
func NewWatchingSecretManager(kubeClient clientset.Interface, resyncInterval time.Duration) Manager {
    listSecret := func(namespace string, opts metav1.ListOptions) (runtime.Object, error) {
        return kubeClient.CoreV1().Secrets(namespace).List(context.TODO(), opts)
    }
    watchSecret := func(namespace string, opts metav1.ListOptions) (watch.Interface, error) {
        return kubeClient.CoreV1().Secrets(namespace).Watch(context.TODO(), opts)
    }
    newSecret := func() runtime.Object {
        return &v1.Secret{}
    }
    isImmutable := func(object runtime.Object) bool {
        if secret, ok := object.(*v1.Secret); ok {
            return secret.Immutable != nil && *secret.Immutable
        }
        return false
    }
    gr := corev1.Resource("secret")
    return &secretManager{
        manager: manager.NewWatchBasedManager(listSecret, watchSecret, newSecret, isImmutable, gr, resyncInterval, getSecretNames),
    }
}

cache_based_manager

/pkg /kubelet /util /manager /cache_based_manager.go

// cacheBasedManager keeps a store with objects necessary
// for registered pods. Different implementations of the store
// may result in different semantics for freshness of objects
// (e.g. ttl-based implementation vs watch-based implementation).
type cacheBasedManager struct {
    objectStore          Store
    getReferencedObjects func(*v1.Pod) sets.String

    lock           sync.Mutex
    registeredPods map[objectKey]*v1.Pod
}

该 manager 代码位于 /pkg /kubelet /util /manager /cache_based_manager.go,属于通用的 Manager 结构体工具,用于保留注册的 Pod 所必要引用的 kubernetes 对象(objects)
如何做到的呢?
通过 getReferencedObjects 字段,一个可以传入的成员函数,自定义实现用于从 v1.Pod 对象中获取到对应对象(或一组对象)的 name。流程如下:

func (c *cacheBasedManager) RegisterPod(pod *v1.Pod) {
    // 1. 获取名字
    names := c.getReferencedObjects(pod)
    c.lock.Lock()
    defer c.lock.Unlock()
    // 2. 给每一个名字和 pod 的命名空间一起添加到 c.objectStore 中存储
    for name := range names {
        c.objectStore.AddReference(pod.Namespace, name)
    }
    // 3. 检查是否之前已经注册了该 Pod
    var prev *v1.Pod
    key := objectKey{namespace: pod.Namespace, name: pod.Name, uid: pod.UID}
    prev = c.registeredPods[key]
    // 4. 用新注册的 pod 替换之前存储的注册 Pod 的信息.
    c.registeredPods[key] = pod
    // 5. 删除旧 Pod 在 c.objectStore 中的引用信息,这是因为在上面第二步 Add 到 c.objectStore
    // 中时,这些资源的引用次数又新增了一次,但实际上只是同一个 Pod 的引用,自然需要删除,当然,也有
    // 可能新 Pod 已经不再引用目标资源了, Delete 函数在下面也处理这个情况
    if prev != nil {
        for name := range c.getReferencedObjects(prev) {
            // On an update, the .Add() call above will have re-incremented the
            // ref count of any existing object, so any objects that are in both
            // names and prev need to have their ref counts decremented. Any that
            // are only in prev need to be completely removed. This unconditional
            // call takes care of both cases.
            c.objectStore.DeleteReference(prev.Namespace, name)
        }
    }
}
  1. 获取名字
  2. 给每一个名字和 pod 的命名空间一起添加到 c.objectStore 中存储
  3. 检查是否之前已经注册了该 Pod
  4. 用新注册的 pod 替换之前存储的注册 Pod 的信息.
  5. 删除旧 Pod 在 c.objectStore 中的引用信息,这是因为在上面第二步 Add 到 c.objectStore 中时,这些资源的引用次数又新增了一次,但实际上只是同一个 Pod 的引用,自然需要删除,当然,也有可能新 Pod 已经不再引用目标资源了, Delete 函数在下面也处理这个情况

ttl ObjectStore

cache_based 的 objectStore 通过 ttl 设置缓存有效期。

watch_based_manager

/pkg /kubelet /util /manager /watch_based_manager.go
可以看到,watch_based_manager 最后使用了 NewCacheBasedManager ,所以 watch_based_manager 和 cache_based_manager 不同的是 ObjectStore 字段。

// NewWatchBasedManager creates a manager that keeps a cache of all objects
// necessary for registered pods.
// It implements the following logic:
// - whenever a pod is created or updated, we start individual watches for all
//   referenced objects that aren't referenced from other registered pods
// - every GetObject() returns a value from local cache propagated via watches
func NewWatchBasedManager(
    listObject listObjectFunc,
    watchObject watchObjectFunc,
    newObject newObjectFunc,
    isImmutable isImmutableFunc,
    groupResource schema.GroupResource,
    resyncInterval time.Duration,
    getReferencedObjects func(*v1.Pod) sets.String) Manager {

    // If a configmap/secret is used as a volume, the volumeManager will visit the objectCacheItem every resyncInterval cycle,
    // We just want to stop the objectCacheItem referenced by environment variables,
    // So, maxIdleTime is set to an integer multiple of resyncInterval,
    // We currently set it to 5 times.
    maxIdleTime := resyncInterval * 5

    // TODO propagate stopCh from the higher level.
    objectStore := NewObjectCache(listObject, watchObject, newObject, isImmutable, groupResource, clock.RealClock{}, maxIdleTime, wait.NeverStop)
    return NewCacheBasedManager(objectStore, getReferencedObjects)
}

watch_based_manager 通过 watch 而不是简单的 ttl 去确认或者刷新缓存。

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