构建后端为etcd的CoreDNS的容器集群（二）、下载最新的etcd容器镜像
在尝试获取etcd的容器的最新版本镜像时，使用latest作为tag取到的并非最新版本，本文尝试用实际最新版本的版本号进行pull，从而取到想的最新版etcd容器镜像。
一、用latest作为tag尝试下载最新etcd的镜像
1、下载镜像
[root@localhost opt]# docker pull quay.io/coreos/etcd:latest
latest: Pulling from coreos/etcd
ff3a5c916c92: Pull complete
96b0e24539ea: Pull complete
d1eca4d01894: Pull complete
ad732d7a61c2: Pull complete
8bc526247b5c: Pull complete
5f56944bb51c: Pull complete
Digest: sha256:5b6691b7225a3f77a5a919a81261bbfb31283804418e187f7116a0a9ef65d21d
Status: Downloaded newer image for quay.io/coreos/etcd:latest2、查看镜像
[root@localhost opt]# docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
quay.io/coreos/etcd latest 61ad63875109 6 years ago 39.5MB显示镜像创建日期为6年前，太离谱了
3、拉一个容器，查看镜像的具体版本
[root@localhost opt]# docker run -d -p 2379:2379 -p 2380:2380 --name etcd quay.io/coreos/etcd /usr/local/bin/etcd -advertise-client-urls http://0.0.0.0:2379 -listen-client-urls http://0.0.0.0:2379 -initial-advertise-peer-urls http://0.0.0.0:2380 -listen-peer-urls http://0.0.0.0:2380 -initial-cluster default=http://0.0.0.0:2380
7874cc64d5aeec551d805bcbc26965d51d3c291a704411b2b604e2735e7fe7a9
[root@localhost opt]# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
7874cc64d5ae quay.io/coreos/etcd "/usr/local/bin/etcd…" 5 seconds ago Up 3 seconds 0.0.0.0:2379-2380->2379-2380/tcp etcd
[root@localhost opt]# docker exec -it etcd /bin/sh
/ #
/ # ps -ef
PID USER TIME COMMAND
1 root 0:00 /usr/local/bin/etcd -advertise-client-urls http://0.0.0.0:2379 -listen-client-urls http://0.0.0.0:2379 -initial-advertise-peer-urls http://0.0.0.0:2380 -listen-peer-urls http://0.0.0.0:2380 -initial-cluster def
18 root 0:00 /bin/sh
29 root 0:00 ps -ef
/ # cd /usr/local/bin/
/usr/local/bin # etcd --version
etcd Version: 3.3.8
Git SHA: 33245c6b5
Go Version: go1.9.7
Go OS/Arch: linux/amd64可见当前容器内的etcd版本为3.3.8，老的离谱。
二、查找etcd最新的正式版版本
查看etcd官方文档Documentation versions | etcd，可以看到当前最新的稳定版本为3.5.16
三、尝试用 3.5.16为tag拉取最新的etcd容器镜像
1、尝试拉取
[root@localhost opt]# docker pull quay.io/coreos/etcd:v3.5.16
v3.5.16: Pulling from coreos/etcd
804c8aba2cc6: Pull complete
2ae710cd8bfe: Pull complete
d462aa345367: Pull complete
0f8b424aa0b9: Pull complete
d557676654e5: Pull complete
c8022d07192e: Pull complete
d858cbc252ad: Pull complete
1069fc2daed1: Pull complete
b40161cd83fc: Pull complete
5318d93a3a65: Pull complete
307c1adadb60: Pull complete
fbb01d9e9dc9: Pull complete
fbfea02ac3cf: Pull complete
8c26e4bf18e2: Pull complete
1e59a65f8816: Pull complete
ffbd4ca5f0bd: Pull complete
Digest: sha256:d967d98a12dc220a1a290794711dba7eba04b8ce465e12b02383d1bfbb33e159
Status: Downloaded newer image for quay.io/coreos/etcd:v3.5.16
[root@localhost opt]# docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
quay.io/coreos/etcd v3.5.16 8523cb381f23 5 weeks ago 59MB可以看到镜像文件创建日期为几周前，应该是比较新了。
2、拉起容器检查应用程序版本
[root@localhost opt]# docker run -d -p 2379:2379 -p 2380:2380 --name etcd quay.io/coreos/etcd:v3.5.16 /usr/local/bin/etcd -advertise-client-urls http://0.0.0.0:2379 -listen-client-urls http://0.0.0.0:2379 -initial-advertise-peer-urls http://0.0.0.0:2380 -listen-peer-urls http://0.0.0.0:2380 -initial-cluster default=http://0.0.0.0:2380
225f0db2c3920b035659878f321f3d3cbda483acf5f11201b96653c48c16a8d5
[root@localhost opt]# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
225f0db2c392 quay.io/coreos/etcd:v3.5.16 "/usr/local/bin/etcd…" 17 minutes ago Up 17 minutes 0.0.0.0:2379-2380->2379-2380/tcp etcd
[root@localhost opt]# docker exec -it etcd /usr/local/bin/etcd --version
etcd Version: 3.5.16
Git SHA: f20bbad
Go Version: go1.22.7
Go OS/Arch: linux/amd64可以看到当前程序包版本确为 3.5.16，达到目的。
总结：当pull拉取镜像时，可能由于镜像源维护的问题，导致用lasted作为tag拉到的并不是该容器的最新版，而需要结合实际应用的版本信息，用目标版本作为tag来pull，才能拿到真正想要的新版本。