【kubernetes/k8s源码分析】 k8s emptydir storage 源码分析

深碍√TFBOYSˉ_ 2022-01-26 12:57 242阅读 0赞

>        EmptyDir 类型：同一个pod内的容器都能读写 EmptyDir 中文件。一旦 pod 离开了宿主机，EmptyDir 中的数据就会被永久删除。所以目前 EmptyDir 类型的 volume主 要用作临时空间。
> 
>       缺省情况下，EmptyDir 是使用主机磁盘进行存储的，需要使用 tmpfs 作为 emptyDir 的可用存储资源也是可以的，只需要在创建 emptyDir 卷时增加一个 emptyDir.medium 字段的定义，并赋值为 "Memory" 即可。

## ##

根据官方给出的建议，emptyDir可以在以下几种场景下使用：

>  *  临时空间，例如基于磁盘的合并排序
>  *  设置检查点以从崩溃事件中恢复未执行完毕的长计算
>  *  保存内容管理器容器从Web服务器容器提供数据时所获取的文件

## ##

### ***$ cat emtptydir.yaml *** ###

> apiVersion: apps/v1  
> kind: Deployment  
> metadata:  
>   name: mysql-emptydir  
>   labels:  
>     app: wordpress-emptydir  
>     tier: mysql-emptydir  
> spec:  
>   selector:  
>     matchLabels:  
>       app: wordpress-emptydir  
>       tier: mysql-emptydir  
>   strategy:  
>     type: Recreate  
>   template:  
>     metadata:  
>       labels:  
>         app: wordpress-emptydir  
>         tier: mysql-emptydir  
>     spec:  
>       containers:  
>         - image: mysql:5.6  
>           name: mysql-emptydir  
>           env:  
>             - name: MYSQL\_ROOT\_PASSWORD  
>               value: changeme  
>           ports:  
>             - containerPort: 3306  
>               name: mysql  
>           volumeMounts:  
>             - name: mysql-persistent-storage  
>               mountPath: /var/lib/mysql  
>       volumes:  
>         - name: mysql-persistent-storage  
>           emptyDir: \{\}

operationExecutor.MountVolume

-->  GenerateMountVolumeFunc

--> volumePlugin.NewMounter （第 1 章节讲解）

--> volumeMounter.SetUp （第 2 章节讲解）

emptyDir 源码实现路径为： pkg/volume/emptydir 目录

emptyDir 插件名称为 kubernetes.io/empty-dir

type emptyDirPlugin struct {
    	host volume.VolumeHost
    }
    
    var _ volume.VolumePlugin = &emptyDirPlugin{}
    
    const (
    	emptyDirPluginName           = "kubernetes.io/empty-dir"
    	hugePagesPageSizeMountOption = "pagesize"
    )
    
    func getPath(uid types.UID, volName string, host volume.VolumeHost) string {
    	return host.GetPodVolumeDir(uid, stringsutil.EscapeQualifiedNameForDisk(emptyDirPluginName), volName)
    }
    
    func (plugin *emptyDirPlugin) Init(host volume.VolumeHost) error {
    	plugin.host = host
    
    	return nil
    }

# 1. NewMounter 函数 #

这个主要实例化 emptyDir 结构，medium数据存储在disk / memory / hugepages

mounter接口实现了 mount umount等一大堆方法

>     StorageMediumDefault   StorageMedium = ""          // use whatever the default is for the node, assume anything we don't explicitly handle is this
>     StorageMediumMemory    StorageMedium = "Memory"    // use memory (e.g. tmpfs on linux)
>     StorageMediumHugePages StorageMedium = "HugePages" // use hugepages

func (plugin *emptyDirPlugin) NewMounter(spec *volume.Spec, pod *v1.Pod, opts volume.VolumeOptions) (volume.Mounter, error) {
    	return plugin.newMounterInternal(spec, pod, plugin.host.GetMounter(plugin.GetPluginName()), &realMountDetector{plugin.host.GetMounter(plugin.GetPluginName())}, opts)
    }
    
    func (plugin *emptyDirPlugin) newMounterInternal(spec *volume.Spec, pod *v1.Pod, mounter mount.Interface, mountDetector mountDetector, opts volume.VolumeOptions) (volume.Mounter, error) {
    	medium := v1.StorageMediumDefault
    
    	if spec.Volume.EmptyDir != nil { // Support a non-specified source as EmptyDir.
    		medium = spec.Volume.EmptyDir.Medium
    	}
    
    	return &emptyDir{
    		pod:             pod,
    		volName:         spec.Name(),
    		medium:          medium,
    		mounter:         mounter,
    		mountDetector:   mountDetector,
    		plugin:          plugin,
    		MetricsProvider: volume.NewMetricsDu(getPath(pod.UID, spec.Name(), plugin.host)),
    	}, nil
    }

# 2. Setup函数 #

就是创建目录，看看SetUpAt进行哪些操作

// SetUp creates new directory.
    func (ed *emptyDir) SetUp(fsGroup *int64) error {
    	return ed.SetUpAt(ed.GetPath(), fsGroup)
    }

# 3. SetUpAt函数 #

###     3.1 IsLikelyNotMountPoint函数验证是否已经mount上了 ###

notMnt, err := ed.mounter.IsLikelyNotMountPoint(dir)
    // Getting an os.IsNotExist err from is a contingency; the directory
    // may not exist yet, in which case, setup should run.
    if err != nil && !os.IsNotExist(err) {
    	return err
    }

###     3.2 根据 medium 类型执行不同操作，分别分析 ###

default 直接 disk，memory hugepages三种

switch ed.medium {
    case v1.StorageMediumDefault:
    	err = ed.setupDir(dir)
    case v1.StorageMediumMemory:
    	err = ed.setupTmpfs(dir)
    case v1.StorageMediumHugePages:
    	err = ed.setupHugepages(dir)
    default:
    	err = fmt.Errorf("unknown storage medium %q", ed.medium)
    }

# 4. setupDir函数 #

创建目录，权限0777，比较简单就是验证权限

// setupDir creates the directory with the default permissions specified by the perm constant.
    func (ed *emptyDir) setupDir(dir string) error {
    	// Create the directory if it doesn't already exist.
    	if err := os.MkdirAll(dir, perm); err != nil {
    		return err
    	}
    
      	// stat the directory to read permission bits
    	fileinfo, err := os.Lstat(dir)
    	if err != nil {
    		return err
    	}

# 5. setupTmpfs函数 #

也需要创建目录，最后也是需要mount操作，将tmpfs挂载到 dir目录

// setupTmpfs creates a tmpfs mount at the specified directory.
    func (ed *emptyDir) setupTmpfs(dir string) error {
    	if ed.mounter == nil {
    		return fmt.Errorf("memory storage requested, but mounter is nil")
    	}
    	if err := ed.setupDir(dir); err != nil {
    		return err
    	}
    	// Make SetUp idempotent.
    	medium, isMnt, err := ed.mountDetector.GetMountMedium(dir)
    	if err != nil {
    		return err
    	}
    	// If the directory is a mountpoint with medium memory, there is no
    	// work to do since we are already in the desired state.
    	if isMnt && medium == v1.StorageMediumMemory {
    		return nil
    	}
    
    	klog.V(3).Infof("pod %v: mounting tmpfs for volume %v", ed.pod.UID, ed.volName)
    	return ed.mounter.Mount("tmpfs", dir, "tmpfs", nil /* options */)
    }

# 总结： #

比较简单，就是pod删除了，数据就没有了

三种模式，默认直接存disk，创建目录

memory 挂载 tmpfs