问题背景：

当前部署了 3 个 etcd 节点，突然有一天 3 台集群全部停电宕机了。重新启动之后发现 K8S 集群是可以正常使用的，但是检查了一遍组件之后，发现有一个节点的 etcd 启动不了。
经过一遍探查，发现时间不准确，通过以下命令 ntpdate ntp.aliyun.com 重新将时间调整正确，重新启动 etcd，发现还是起不来，报错如下：
Mar 05 14:27:15 k8s-node2 etcd[3248]: etcd Version: 3.3.13
Mar 05 14:27:15 k8s-node2 etcd[3248]: Git SHA: 98d3084
Mar 05 14:27:15 k8s-node2 etcd[3248]: Go Version: go1.10.8
Mar 05 14:27:15 k8s-node2 etcd[3248]: Go OS/Arch: linux/amd64
Mar 05 14:27:15 k8s-node2 etcd[3248]: setting maximum number of CPUs to 4, total number of available CPUs is 4
Mar 05 14:27:15 k8s-node2 etcd[3248]: the server is already initialized as member before, starting as etcd member
…
Mar 05 14:27:15 k8s-node2 etcd[3248]: peerTLS: cert = /opt/etcd/ssl/server.pem, key = /opt/etcd/ssl/server-key.pe
m, ca = , trusted-ca = /opt/etcd/ssl/ca.pem, client-cert-auth = false, crl-file =
Mar 05 14:27:15 k8s-node2 etcd[3248]: listening for peers on https://192.168.25.226:2380
Mar 05 14:27:15 k8s-node2 etcd[3248]: The scheme of client url http://127.0.0.1:2379 is HTTP while peer key/cert
files are presented. Ignored key/cert files.
Mar 05 14:27:15 k8s-node2 etcd[3248]: listening for client requests on 127.0.0.1:2379
Mar 05 14:27:15 k8s-node2 etcd[3248]: listening for client requests on 192.168.25.226:2379
Mar 05 14:27:15 k8s-node2 etcd[3248]: member 9c166b8b7cb6ecb8 has already been bootstrapped
Mar 05 14:27:15 k8s-node2 systemd[1]: etcd.service: main process exited, code=exited, status=1/FAILURE
Mar 05 14:27:15 k8s-node2 systemd[1]: Failed to start Etcd Server.
Mar 05 14:27:15 k8s-node2 systemd[1]: Unit etcd.service entered failed state.
Mar 05 14:27:15 k8s-node2 systemd[1]: etcd.service failed.
Mar 05 14:27:15 k8s-node2 systemd[1]: etcd.service failed.
Mar 05 14:27:15 k8s-node2 systemd[1]: etcd.service holdoff time over, scheduling restart.
Mar 05 14:27:15 k8s-node2 systemd[1]: Starting Etcd Server…
Mar 05 14:27:15 k8s-node2 etcd[3258]: recognized environment variable ETCD_NAME, but unused: shadowed by correspo
nding flag
Mar 05 14:27:15 k8s-node2 etcd[3258]: recognized environment variable ETCD_DATA_DIR, but unused: shadowed by corr
esponding flag
Mar 05 14:27:15 k8s-node2 etcd[3258]: recognized environment variable ETCD_LISTEN_PEER_URLS, but unused: shadowed
by corresponding flag
Mar 05 14:27:15 k8s-node2 etcd[3258]: recognized environment variable ETCD_LISTEN_CLIENT_URLS, but unused: shadow
ed by corresponding flag
Mar 05 14:27:15 k8s-node2 etcd[3258]: recognized environment variable ETCD_INITIAL_ADVERTISE_PEER_URLS, but unuse
d: shadowed by corresponding flag
Mar 05 14:27:15 k8s-node2 etcd[3258]: recognized environment variable ETCD_ADVERTISE_CLIENT_URLS, but unused: sha
dowed by corresponding flag
Mar 05 14:27:15 k8s-node2 etcd[3258]: recognized environment variable ETCD_INITIAL_CLUSTER, but unused: shadowed
by corresponding flag
Mar 05 14:27:15 k8s-node2 etcd[3258]: recognized environment variable ETCD_INITIAL_CLUSTER_TOKEN, but unused: sha
dowed by corresponding flag
Mar 05 14:27:15 k8s-node2 etcd[3258]: recognized environment variable ETCD_INITIAL_CLUSTER_STATE, but unused: sha
dowed by corresponding flag

解决方法：

检查日志发现并没有特别明显的错误，根据经验来讲，etcd 节点坏掉一个其实对集群没有大的影响，这时集群已经可以正常使用了，但是这个坏掉的 etcd 节点并没有启动，解决方法如下：
进入 etcd 的数据存储目录进行备份 备份原有数据：
cd /var/lib/etcd/default.etcd/member/
cp * /data/bak/
删除这个目录下的所有数据文件
rm -rf /var/lib/etcd/default.etcd/member/*
停止另外两台 etcd 节点，因为 etcd 节点启动时需要所有节点一起启动，启动成功后即可使用。
#master 节点
systemctl stop etcd
systemctl restart etcd

#node1 节点
systemctl stop etcd
systemctl restart etcd

#node2 节点
systemctl stop etcd
systemctl restart etcd