hostPath允许挂载Node上的文件系统到Pod里面去。如果Pod有需要使用Node上的东西，可以使用hostPath

 

hostPath 的用途如下：

• 运行需要访问 Docker 内部的容器；使用 /var/lib/docker 的 hostPath
• 在容器中运行 cAdvisor；使用 /dev/cgroups 的 hostPath

 

为 hostPath 卷指定 type

值	行为
	空字符串（默认）用于向后兼容，在挂载 hostPath 卷之前不会执行任何检查
DirectoryOrCreate	将根据需要在那里创建一个空目录，权限设置为 0755，与 Kubelet 具有相同的组和权限
Directory	给定的路径下必须存在目录
FileOrCreate	会根据需要创建一个空文件，权限设置为 0644，与 Kubelet 具有相同的组和权限
File	给定的路径下必须存在文件
Socket	给定的路径下必须存在 UNIX 套接字
CharDevice	给定的路径下必须存在字符设备
BlockDevice	给定的路径下必须存在块设备

 

 $ cat hostpath.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: mysql-hostpath
  labels:
    app: wordpress-hostpath
    tier: mysql-hostpath
spec:
  selector:
    matchLabels:
      app: wordpress-hostpath
      tier: mysql-hostpath
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: wordpress-hostpath
        tier: mysql-hostpath
    spec:
      containers:
        - image: mysql:5.6
          name: mysql-hostpath
          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
          hostPath:
            path: /tmp/mysql

 

    插件名称：kubernetes.io/host-path

 

1. NewMounter

   实例化 hostPathMounter，包括路径，类型，是否只读等

func (plugin *hostPathPlugin) NewMounter(spec *volume.Spec, pod *v1.Pod, opts volume.VolumeOptions) (volume.Mounter, error) {
	hostPathVolumeSource, readOnly, err := getVolumeSource(spec)
	if err != nil {
		return nil, err
	}

	path := hostPathVolumeSource.Path
	pathType := new(v1.HostPathType)
	if hostPathVolumeSource.Type == nil {
		*pathType = v1.HostPathUnset
	} else {
		pathType = hostPathVolumeSource.Type
	}
	return &hostPathMounter{
		hostPath: &hostPath{path: path, pathType: pathType},
		readOnly: readOnly,
		mounter:  plugin.host.GetMounter(plugin.GetPluginName()),
	}, nil
}

 

   path 支持的 type，上面表格有解释

// For backwards compatible, leave it empty if unset
HostPathUnset HostPathType = ""
// If nothing exists at the given path, an empty directory will be created there
// as needed with file mode 0755, having the same group and ownership with Kubelet.
HostPathDirectoryOrCreate HostPathType = "DirectoryOrCreate"
// A directory must exist at the given path
HostPathDirectory HostPathType = "Directory"
// If nothing exists at the given path, an empty file will be created there
// as needed with file mode 0644, having the same group and ownership with Kubelet.
HostPathFileOrCreate HostPathType = "FileOrCreate"
// A file must exist at the given path
HostPathFile HostPathType = "File"
// A UNIX socket must exist at the given path
HostPathSocket HostPathType = "Socket"
// A character device must exist at the given path
HostPathCharDev HostPathType = "CharDevice"
// A block device must exist at the given path
HostPathBlockDev HostPathType = "BlockDevice"

 

2. SetUp

      这个实现如果使用mount就是多此一举，直接创建目录就好了，看看怎么实现的，如果类型为设置为“”，则不处理，创建则直接交给docker daemon就好了

// SetUp does nothing.
func (b *hostPathMounter) SetUp(fsGroup *int64) error {
	err := validation.ValidatePathNoBacksteps(b.GetPath())
	if err != nil {
		return fmt.Errorf("invalid HostPath `%s`: %v", b.GetPath(), err)
	}

	if *b.pathType == v1.HostPathUnset {
		return nil
	}
	return checkType(b.GetPath(), b.pathType, b.mounter)
}

    如果设置则检查什么类型的，则如下处理，无非就是创建目录，文件等操作

func checkTypeInternal(ftc hostPathTypeChecker, pathType *v1.HostPathType) error {
	switch *pathType {
	case v1.HostPathDirectoryOrCreate:
		if !ftc.Exists() {
			return ftc.MakeDir()
		}
		fallthrough
	case v1.HostPathDirectory:
		if !ftc.IsDir() {
			return fmt.Errorf("hostPath type check failed: %s is not a directory", ftc.GetPath())
		}
	case v1.HostPathFileOrCreate:
		if !ftc.Exists() {
			return ftc.MakeFile()
		}
		fallthrough
	case v1.HostPathFile:
		if !ftc.IsFile() {
			return fmt.Errorf("hostPath type check failed: %s is not a file", ftc.GetPath())
		}
	case v1.HostPathSocket:
		if !ftc.IsSocket() {
			return fmt.Errorf("hostPath type check failed: %s is not a socket file", ftc.GetPath())
		}
	case v1.HostPathCharDev:
		if !ftc.IsChar() {
			return fmt.Errorf("hostPath type check failed: %s is not a character device", ftc.GetPath())
		}
	case v1.HostPathBlockDev:
		if !ftc.IsBlock() {
			return fmt.Errorf("hostPath type check failed: %s is not a block device", ftc.GetPath())
		}
	default:
		return fmt.Errorf("%s is an invalid volume type", *pathType)
	}

	return nil
}

 

参考：

• https://kubernetes.io/docs/concepts/storage/volumes/