Docker 鏡像是由多個文件系統（只讀層）疊加而成，每個層僅包含了前一層的差異部分 。當我們啟動一個容器的時候，Docker 會加載鏡像層并在其上添加一個可寫層 。容器上所做的任何更改，譬如新建文件、更改文件、刪除文件，都將記錄與可寫層上 。當我們使docker save形式嘗試導出鏡像時會導出該鏡像的所有文件層 ， 當然這個行為是必要的，因為你不知道這個鏡像的被導入環境是否已包含基礎鏡像的文件層 。但是如果我們有一批鏡像且都依賴某一個或兩個基礎鏡像構建，且不具備批量 save的調價（必須一個一個分開了打包），這種情況下如果一個一個save的話對硬盤資源是極大的浪費，那么有沒有辦法去掉哪些重復的鏡像層呢 ， 答案是OK的 。（也許有人會吐槽為啥不用docekrfile呢，是的一般情況下是ok的，但是用dockerfile build出來的鏡像id時不一樣的）
看下docker save 導出了寫啥以如下鏡像為例子
FROM centos:7COPY main /home/mainRUN chmod +x /home/mainCMD /home/mai【精簡docker的導出鏡像】構建
docker build -t ip-server:1.0.0 .導出
[root@localhost demo]# docker save -o ip-server.tar ip-server:1.0.0[root@localhost demo]# du -sh ip-server.tar212M ip-server.tar[root@localhost demo]# docker save -o centos7.tar centos:7[root@localhost demo]# du -sh centos7.tar202M centos7.tar可以看到基于centos7構建的ip-server鏡像只是大了一?。簿褪俏頤荂OPY進來的一個可執行文件大??，那脜舱涢惇眽募入环境存在centos7鏡像的文件層是該如何減小ip-server.tar的體積呢？
拆解導出的鏡像[root@localhost demo]# mkdir ip-server && tar xf ip-server.tar -C ip-server[root@localhost demo]# tree ip-serverip-server├── 3efdc87cec68e28bccf6c0d96894c903e12157ed0797651a2eaa565108de5bd8│   ├── json│   ├── layer.tar -> ../fad57ccc4dd192e49d3979f477525a4b4c8fb8532ae31c2c74b5403474a26e4d/layer.tar│   └── VERSION├── d8f46057879e2e8614caa5511934d403d7ebea0af9b196bf29b68161fda76766│   ├── json│   ├── layer.tar│   └── VERSION├── f898e9c3d94a1617bac63c962155327671957f2bcbd35e6411153b7730d6558e.json├── fad57ccc4dd192e49d3979f477525a4b4c8fb8532ae31c2c74b5403474a26e4d│   ├── json│   ├── layer.tar│   └── VERSION├── manifest.json└── repositories3 directories, 12 files# manifest.json[{"Config": "f898e9c3d94a1617bac63c962155327671957f2bcbd35e6411153b7730d6558e.json","RepoTags": ["ip-server:1.0.0"],"Layers": ["d8f46057879e2e8614caa5511934d403d7ebea0af9b196bf29b68161fda76766/layer.tar","fad57ccc4dd192e49d3979f477525a4b4c8fb8532ae31c2c74b5403474a26e4d/layer.tar","3efdc87cec68e28bccf6c0d96894c903e12157ed0797651a2eaa565108de5bd8/layer.tar"]}]# f898e9c3d94a1617bac63c962155327671957f2bcbd35e6411153b7730d6558e.json{"architecture": "amd64","config": {"Hostname": "","Domainname": "","User": "","AttachStdin": false,"AttachStdout": false,"AttachStderr": false,"Tty": false,"OpenStdin": false,"StdinOnce": false,"Env": ["PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"],"Cmd": ["/bin/sh","-c","/home/main"],"Image": "sha256:04da435eb95c963effbf9aba060e6f2ddd962b4861ce1bf7bdc5f3cbffceb4b5","Volumes": null,"WorkingDir": "","Entrypoint": null,"OnBuild": null,"Labels": {"org.label-schema.build-date": "20201113","org.label-schema.license": "GPLv2","org.label-schema.name": "CentOS Base Image","org.label-schema.schema-version": "1.0","org.label-schema.vendor": "CentOS","org.opencontainers.image.created": "2020-11-13 00:00:00+00:00","org.opencontainers.image.licenses": "GPL-2.0-only","org.opencontainers.image.title": "CentOS Base Image","org.opencontainers.image.vendor": "CentOS"}},"container": "5d3e8d3176babbe767294d6834bf1dc6e64ce9838bc08993751724a92231d6ac","container_config": {"Hostname": "5d3e8d3176ba","Domainname": "","User": "","AttachStdin": false,"AttachStdout": false,"AttachStderr": false,"Tty": false,"OpenStdin": false,"StdinOnce": false,"Env": ["PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"],"Cmd": ["/bin/sh","-c","#(nop) ","CMD [\"/bin/sh\" \"-c\" \"/home/main\"]"],"Image": "sha256:04da435eb95c963effbf9aba060e6f2ddd962b4861ce1bf7bdc5f3cbffceb4b5","Volumes": null,"WorkingDir": "","Entrypoint": null,"OnBuild": null,"Labels": {"org.label-schema.build-date": "20201113","org.label-schema.license": "GPLv2","org.label-schema.name": "CentOS Base Image","org.label-schema.schema-version": "1.0","org.label-schema.vendor": "CentOS","org.opencontainers.image.created": "2020-11-13 00:00:00+00:00","org.opencontainers.image.licenses": "GPL-2.0-only","org.opencontainers.image.title": "CentOS Base Image","org.opencontainers.image.vendor": "CentOS"}},"created": "2022-10-26T15:53:47.898864929Z","docker_version": "20.10.17","history": [{"created": "2021-09-15T18:20:23.417639551Z","created_by": "/bin/sh -c #(nop) ADD file:b3ebbe8bd304723d43b7b44a6d990cd657b63d93d6a2a9293983a30bfc1dfa53 in / "},{"created": "2021-09-15T18:20:23.819893035Z","created_by": "/bin/sh -c #(nop)LABEL org.label-schema.schema-version=1.0 org.label-schema.name=CentOS Base Image org.label-schema.vendor=CentOS org.label-schema.license=GPLv2 org.label-schema.build-date=20201113 org.opencontainers.image.title=CentOS Base Image org.opencontainers.image.vendor=CentOS org.opencontainers.image.licenses=GPL-2.0-only org.opencontainers.image.created=2020-11-13 00:00:00+00:00","empty_layer": true},{"created": "2021-09-15T18:20:23.99863383Z","created_by": "/bin/sh -c #(nop)CMD [\"/bin/bash\"]","empty_layer": true},{"created": "2022-10-26T15:53:46.693528022Z","created_by": "/bin/sh -c #(nop) COPY file:d0c12b416e2bad24636a0f240cc09c4a6b6a0def701b5aaeeca4963507e468c4 in /home/main "},{"created": "2022-10-26T15:53:47.752968676Z","created_by": "/bin/sh -c chmod +x /home/main"},{"created": "2022-10-26T15:53:47.898864929Z","created_by": "/bin/sh -c #(nop)CMD [\"/bin/sh\" \"-c\" \"/home/main\"]","empty_layer": true}],"os": "linux","rootfs": {"type": "layers","diff_ids": ["sha256:174f5685490326fc0a1c0f5570b8663732189b327007e47ff13d2ca59673db02","sha256:185d24f4ae72bebf9b31c3d26486d52163e38e6c09167507a6a4f28d491aeb28","sha256:185d24f4ae72bebf9b31c3d26486d52163e38e6c09167507a6a4f28d491aeb28"]}}