一、问题背景

1. 当前Cluster K8s Version： v1.17.4
2. 需要升级到K8s Version：v1.19.3
3. 在升级过程中，有个Pod卡在ContainerCreating状态

api-9flnb                             0/1     ContainerCreating   0          4d19h
api-bb8th                             1/1     Running             0          4d20h
api-zwtpp                             1/1     Running             0          4d20h

二、问题分析

1. Describe该Pod状态，提示hostPath type check failed: /var/run/docker.sock is not a file

   Events:
     Type     Reason       Age                       From     Message
     ----     ------       ----                      ----     -------
     Warning  FailedMount  11m (x3543 over 4d18h)    kubelet  (combined from similar events): Unable to attach or mount volumes: unmounted volumes=[docker-socket], unattached volumes=[xxxx-service-account-token-rjqz7 nginx-certs host-timezone docker-socket helm-home etc-pki kubernetes-root-ca-file root-ca-file bcmt-home etcd-client-certs]: timed out waiting for the condition
     Warning  FailedMount  2m39s (x2889 over 4d19h)  kubelet  MountVolume.SetUp failed for volume "docker-socket" : hostPath type check failed: /var/run/docker.sock is not a file

2. 查看该Pod中volume "docker-socket"的声明，Path是/var/run/docker.sock，HostPathType是File

   Volumes:
     etcd-client-certs:
       Type:        Secret (a volume populated by a Secret)
       SecretName:  etcd-client-certs
       Optional:    false
     nginx-certs:
       Type:          HostPath (bare host directory volume)
       Path:          /opt/bcmt/config/bcmt-api/certs
       HostPathType:  Directory
     docker-socket:
       Type:          HostPath (bare host directory volume)
       Path:          /var/run/docker.sock
       HostPathType:  File

3. 查看K8s从v1.17.4到v1.19.3关于Type检测方面的相关代码变化

首先，报错的代码函数是checkTypeInternal(),在文件host_path.go定义，会判断HostPathType和实际Type是否一致，否则报错。

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
}

然后，结合我们pod的定义，HostPathType是File，但是实际Path文件/var/run/docker.sock应该是Socket，所以报错是正确的。疑问在于，为什么v1.17.4没有报错（亲测v1.18.x也不会报错），而到了v1.19.3才开始报错？？？

• 检查checkTypeInternal函数代码有无改动，---> 结果是无改动
• 检查入参hostPathTypeChecker传值是否有改动， --->发现有改动
• v1.17.x和v1.18.x中，IsFile()定义如下

• func (ftc *fileTypeChecker) IsFile() bool {
      if !ftc.Exists() {
          return false
      }
      return !ftc.IsDir()
  }

   
• v1.19.x开始，IsFile()更新如下

func (ftc *fileTypeChecker) IsFile() bool {
    if !ftc.Exists() {
        return false
    }
    pathType, err := ftc.hu.GetFileType(ftc.path)
    if err != nil {
        return false
    }
    return string(pathType) == string(v1.HostPathFile)
}

三、问题结论

1. K8s从v1.19.x修复了IsFile()函数检测功能不完备的Bug；
2. 我们的Pod Mount Volume 文件.sock时指定HostPathType错误（应该是Socket, 不应该是File），但是在v1.19.x之前因为k8s的bug正好将错就错反而没有问题，等v1.19.x修复了该Bug就会出现Volume Mount失败的问题

四、解决方案：.sock文件的HostPathType要设置成Socket

Volumes:
  docker-socket:
    Type:          HostPath (bare host directory volume)
    Path:          /var/run/docker.sock
    HostPathType:  Socket