Events:
Type Reason Age From Message

Normal Scheduled 37s default-scheduler Successfully assigned test/liveness to ubuntu-slave1
Normal Pulling 14s (x2 over 35s) kubelet Pulling image "song.kubeimooc.com/library/liveness"
Warning Failed 14s (x2 over 29s) kubelet Failed to pull image “song.kubeimooc.com/library/liveness”: rpc error: code = Unknown desc = Error response from daemon: Get https://song.kubeimooc.com/v2/: dial tcp: lookup song.kubeimooc.com: no such host
Warning Failed 14s (x2 over 29s) kubelet Error: ErrImagePull
Normal BackOff 2s (x2 over 29s) kubelet Back-off pulling image "song.kubeimooc.com/library/liveness"
Warning Failed 2s (x2 over 29s) kubelet Error: ImagePullBackOff

这个错误是什么原因