更新失败，显示“gnutls_handshake() 失败：拉取函数出错。”

Question

我是 Ubuntu 和 Kubernetes 的新手。当我尝试配置 Kubernetes 集群时，命令update失败并显示以下消息：

$ sudo apt-get update
Err:9 ht#tps://packages.cloud.google.com/apt kubernetes-xenial/main amd64 Packages
  gnutls_handshake() failed: Error in the pull function.
Reading package lists... Done
W: The repository 'http://apt.kubernetes.io kubernetes-xenial Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: Failed to fetch https://packages.cloud.google.com/apt/dists/kubernetes-xenial/main/binary-amd64/Packages  gnutls_handshake() failed: Error in the pull function.
E: Failed to fetch https://packages.cloud.google.com/apt/dists/kubernetes-xenial/main/i18n/Translation-en  gnutls_handshake() failed: Error in the pull function.
E: Some index files failed to download. They have been ignored, or old ones used instead.

^{（这不是完整的输出。我只保留了错误消息。）}

有人可以帮助我理解并解决这个问题吗？