【Docker】從零開始：8.Docker命令:Commit命令
- 基本概念
- 鏡像
- 鏡像分層
- 什么是鏡像分層
- 為什么 Docker 鏡像要采用這種分層結構
- 本章要點
- commit 命令
- 命令格式
- docker commit 操作參數
- 實例演示
- 1.下載一個新的ubuntu鏡像
- 2.運行容器
- 3.查看并安裝vim
- 4.退出容器
- 5提交自己的鏡像
- 對比
- 總結
了解commit命令之前我們先了解下涉及的相關知識
為什么這里又說鏡像，因為之前了解的只是個大概，現在涉及鏡像的原理
基本概念
鏡像
- 是一種輕量級、可執行的獨立軟件包，它包含運行某個軟件所需的所有內容，我們把應用程序和配置依賴打包好形成一個可交付的運行環境(包括代碼、運行時需要的庫、環境變量和配置文件等)，這個打包好的運行環境就是image鏡像文件。
- 只有通過這個鏡像文件才能生成Docker容器實例(類似Java中new出來一個對象)。
鏡像分層
什么是鏡像分層
- “鏡像是有分層的”
- 如圖所示：
- 如圖所示：
- 鏡像的使用的文件技術是UnionFS
- UnionFS（聯合文件系統）
- UnionFS（聯合文件系統）：Union文件系統（UnionFS）是一種分層、輕量級并且高性能的文件系統，它支持對文件系統的修改作為一次提交來一層層的疊加，同時可以將不同目錄掛載到同一個虛擬文件系統下(unite several directories into a single virtual filesystem)。Union 文件系統是 Docker 鏡像的基礎。鏡像可以通過分層來進行繼承，基于基礎鏡像（沒有父鏡像），可以制作各種具體的應用鏡像。
- 特性：一次同時加載多個文件系統，但從外面看起來，只能看到一個文件系統，聯合加載會把各層文件系統疊加起來，這樣最終的文件系統會包含所有底層的文件和目錄
- UnionFS（聯合文件系統）
- Docker鏡像加載原理：
- Docker的鏡像實際上由一層一層的文件系統組成，這種層級的文件系統UnionFS。
- Bootfs(boot file system)主要包含bootloader和kernel, bootloader主要是引導加載kernel, Linux剛啟動時會加載bootfs文件系統，在Docker鏡像的最底層是引導文件系統bootfs。這一層與我們典型的Linux/Unix系統是一樣的，包含boot加載器和內核。當boot加載完成之后整個內核就都在內存中了，此時內存的使用權已由bootfs轉交給內核，此時系統也會卸載Bootfs。
- rootfs (root file system) ，在bootfs之上。包含的就是典型 Linux 系統中的 /dev, /proc, /bin, /etc 等標準目錄和文件。rootfs就是各種不同的操作系統發行版，比如Ubuntu，Centos等等。
對于一個精簡的OS，rootfs可以很小，只需要包括最基本的命令、工具和程序庫就可以了，因為底層直接用Host的kernel，自己只需要提供 rootfs 就行了。由此可見對于不同的linux發行版, bootfs基本是一致的, rootfs會有差別, 因此不同的發行版可以公用bootfs。
為什么 Docker 鏡像要采用這種分層結構
- 比如說有多個鏡像都從相同的 base 鏡像構建而來，那么 Docker Host 只需在磁盤上保存一份 base 鏡像；
同時內存中也只需加載一份 base 鏡像，就可以為所有容器服務了。而且鏡像的每一層都可以被共享。
本章要點
- Docker鏡像層都是只讀的，容器層是可寫的。
- 當容器啟動時，一個新的可寫層被加載到鏡像的頂部。這一層通常被稱作“容器層”，“容器層”之下的都叫“鏡像層”。
- 所有對容器的改動 - 無論添加、刪除、還是修改文件都只會發生在容器層中。只有容器層是可寫的，容器層下面的所有鏡像層都是只讀的。
commit 命令
- docker commit 命令用于根據 Docker容器 的更改創建一個新的 Dokcer鏡像。該命令后面的 CONTAINER 可以是容器Id，或者是容器名。
命令格式
docker commit -m="[提交的描述信息]" -a="[作者]" [容器ID] [新的鏡像名稱]:[新的鏡像標簽]
docker commit 操作參數
| 參數 | 描述 |
|---|---|
| -a, --author string | 作者。 |
| -c, --change list | 應用 dockerfile 指令來創建圖像。 |
| -m, --message | string |
| -p, --pause | 提交期間暫停容器（默認為true）。 |
實例演示
1.下載一個新的ubuntu鏡像
[root@docker ~]# docker search ubuntu
NAME DESCRIPTION STARS OFFICIAL AUTOMATED
ubuntu Ubuntu is a Debian-based Linux operating sys… 16622 [OK]
websphere-liberty WebSphere Liberty multi-architecture images … 297 [OK]
open-liberty Open Liberty multi-architecture images based… 62 [OK]
neurodebian NeuroDebian provides neuroscience research s… 105 [OK]
ubuntu-debootstrap DEPRECATED; use "ubuntu" instead 52 [OK]
ubuntu-upstart DEPRECATED, as is Upstart (find other proces… 115 [OK]
ubuntu/nginx Nginx, a high-performance reverse proxy & we… 102
ubuntu/squid Squid is a caching proxy for the Web. Long-t… 70
ubuntu/cortex Cortex provides storage for Prometheus. Long… 4
ubuntu/apache2 Apache, a secure & extensible open-source HT… 65
ubuntu/prometheus Prometheus is a systems and service monitori… 51
ubuntu/kafka Apache Kafka, a distributed event streaming … 37
ubuntu/bind9 BIND 9 is a very flexible, full-featured DNS… 64
ubuntu/mysql MySQL open source fast, stable, multi-thread… 54
ubuntu/zookeeper ZooKeeper maintains configuration informatio… 12
ubuntu/postgres PostgreSQL is an open source object-relation… 31
ubuntu/redis Redis, an open source key-value store. Long-… 21
ubuntu/jre Distroless Java runtime based on Ubuntu. Lon… 9
ubuntu/grafana Grafana, a feature rich metrics dashboard & … 9
ubuntu/dotnet-aspnet Chiselled Ubuntu runtime image for ASP.NET a… 13
ubuntu/memcached Memcached, in-memory keyvalue store for smal… 5
ubuntu/dotnet-deps Chiselled Ubuntu for self-contained .NET & A… 11
ubuntu/prometheus-alertmanager Alertmanager handles client alerts from Prom… 9
ubuntu/dotnet-runtime Chiselled Ubuntu runtime image for .NET apps… 13
ubuntu/cassandra Cassandra, an open source NoSQL distributed … 2
[root@docker ~]# docker pull ubuntu
Using default tag: latest
latest: Pulling from library/ubuntu
7b1a6ab2e44d: Pull complete
Digest: sha256:626ffe58f6e7566e00254b638eb7e0f3b11d4da9675088f4781a50ae288f3322
Status: Downloaded newer image for ubuntu:latest
docker.io/library/ubuntu:latest
[root@docker ~]#
2.運行容器
[root@docker ~]# docker run -it ba6acccedd29 /bin/bash
root@792de8cbe835:/#
3.查看并安裝vim
[root@docker ~]# docker run -it ba6acccedd29 /bin/bash
root@ce128f008eea:/# vim aaa.txt
oot@ce128f008eea:/# apt-get update
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Reading package lists... Done
root@ce128f008eea:/# apt-get install -y vim
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:alsa-topology-conf alsa-ucm-conf file libasound2 libasound2-data libcanberra0 libexpat1 libgpm2 libltdl7 libmagic-mgc libmagic1 libmpdec2 libogg0 libpython3.8 libpython3.8-minimal libpython3.8-stdlib libreadline8 libsqlite3-0 libssl1.1 libtdb1 libvorbis0a libvorbisfile3 mime-support readline-common sound-theme-freedesktopvim-common vim-runtime xxd xz-utils
Suggested packages:libasound2-plugins alsa-utils libcanberra-gtk0 libcanberra-pulse gpm readline-doc ctags vim-doc vim-scripts
The following NEW packages will be installed:alsa-topology-conf alsa-ucm-conf file libasound2 libasound2-data libcanberra0 libexpat1 libgpm2 libltdl7 libmagic-mgc libmagic1 libmpdec2 libogg0 libpython3.8 libpython3.8-minimal libpython3.8-stdlib libreadline8 libsqlite3-0 libssl1.1 libtdb1 libvorbis0a libvorbisfile3 mime-support readline-common sound-theme-freedesktop vimvim-common vim-runtime xxd xz-utils
0 upgraded, 30 newly installed, 0 to remove and 51 not upgraded.
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update-alternatives: warning: skip creation of /usr/share/man/man1/lzma.1.gz because associated file /usr/share/man/man1/xz.1.gz (of link group lzma) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/unlzma.1.gz because associated file /usr/share/man/man1/unxz.1.gz (of link group lzma) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/lzcat.1.gz because associated file /usr/share/man/man1/xzcat.1.gz (of link group lzma) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/lzmore.1.gz because associated file /usr/share/man/man1/xzmore.1.gz (of link group lzma) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/lzless.1.gz because associated file /usr/share/man/man1/xzless.1.gz (of link group lzma) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/lzdiff.1.gz because associated file /usr/share/man/man1/xzdiff.1.gz (of link group lzma) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/lzcmp.1.gz because associated file /usr/share/man/man1/xzcmp.1.gz (of link group lzma) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/lzgrep.1.gz because associated file /usr/share/man/man1/xzgrep.1.gz (of link group lzma) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/lzegrep.1.gz because associated file /usr/share/man/man1/xzegrep.1.gz (of link group lzma) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/lzfgrep.1.gz because associated file /usr/share/man/man1/xzfgrep.1.gz (of link group lzma) doesn't exist
Setting up libvorbis0a:amd64 (1.3.6-2ubuntu1) ...
Setting up libltdl7:amd64 (2.4.6-14) ...
Setting up alsa-topology-conf (1.2.2-1) ...
Setting up sound-theme-freedesktop (0.8-2ubuntu1) ...
Setting up libasound2:amd64 (1.2.2-2.1ubuntu2.5) ...
Setting up libmpdec2:amd64 (2.4.2-3) ...
Setting up vim-runtime (2:8.1.2269-1ubuntu5.20) ...
Setting up readline-common (8.0-4) ...
Setting up libpython3.8-minimal:amd64 (3.8.10-0ubuntu1~20.04.8) ...
Setting up libreadline8:amd64 (8.0-4) ...
Setting up libvorbisfile3:amd64 (1.3.6-2ubuntu1) ...
Setting up libpython3.8-stdlib:amd64 (3.8.10-0ubuntu1~20.04.8) ...
Setting up libcanberra0:amd64 (0.30-7ubuntu1) ...
Setting up libpython3.8:amd64 (3.8.10-0ubuntu1~20.04.8) ...
Setting up vim (2:8.1.2269-1ubuntu5.20) ...
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/vim (vim) in auto mode
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/vimdiff (vimdiff) in auto mode
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/rvim (rvim) in auto mode
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/rview (rview) in auto mode
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/vi (vi) in auto mode
update-alternatives: warning: skip creation of /usr/share/man/da/man1/vi.1.gz because associated file /usr/share/man/da/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/de/man1/vi.1.gz because associated file /usr/share/man/de/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/fr/man1/vi.1.gz because associated file /usr/share/man/fr/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/it/man1/vi.1.gz because associated file /usr/share/man/it/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ja/man1/vi.1.gz because associated file /usr/share/man/ja/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/pl/man1/vi.1.gz because associated file /usr/share/man/pl/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ru/man1/vi.1.gz because associated file /usr/share/man/ru/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/vi.1.gz because associated file /usr/share/man/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/view (view) in auto mode
update-alternatives: warning: skip creation of /usr/share/man/da/man1/view.1.gz because associated file /usr/share/man/da/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/de/man1/view.1.gz because associated file /usr/share/man/de/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/fr/man1/view.1.gz because associated file /usr/share/man/fr/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/it/man1/view.1.gz because associated file /usr/share/man/it/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ja/man1/view.1.gz because associated file /usr/share/man/ja/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/pl/man1/view.1.gz because associated file /usr/share/man/pl/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ru/man1/view.1.gz because associated file /usr/share/man/ru/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/view.1.gz because associated file /usr/share/man/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/ex (ex) in auto mode
update-alternatives: warning: skip creation of /usr/share/man/da/man1/ex.1.gz because associated file /usr/share/man/da/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/de/man1/ex.1.gz because associated file /usr/share/man/de/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/fr/man1/ex.1.gz because associated file /usr/share/man/fr/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/it/man1/ex.1.gz because associated file /usr/share/man/it/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ja/man1/ex.1.gz because associated file /usr/share/man/ja/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/pl/man1/ex.1.gz because associated file /usr/share/man/pl/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ru/man1/ex.1.gz because associated file /usr/share/man/ru/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/ex.1.gz because associated file /usr/share/man/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/editor (editor) in auto mode
update-alternatives: warning: skip creation of /usr/share/man/da/man1/editor.1.gz because associated file /usr/share/man/da/man1/vim.1.gz (of link group editor) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/de/man1/editor.1.gz because associated file /usr/share/man/de/man1/vim.1.gz (of link group editor) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/fr/man1/editor.1.gz because associated file /usr/share/man/fr/man1/vim.1.gz (of link group editor) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/it/man1/editor.1.gz because associated file /usr/share/man/it/man1/vim.1.gz (of link group editor) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ja/man1/editor.1.gz because associated file /usr/share/man/ja/man1/vim.1.gz (of link group editor) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/pl/man1/editor.1.gz because associated file /usr/share/man/pl/man1/vim.1.gz (of link group editor) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ru/man1/editor.1.gz because associated file /usr/share/man/ru/man1/vim.1.gz (of link group editor) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/editor.1.gz because associated file /usr/share/man/man1/vim.1.gz (of link group editor) doesn't exist
Processing triggers for libc-bin (2.31-0ubuntu9.2) ...
root@ce128f008eea:/#
4.退出容器
root@ce128f008eea:/# exit
exit
[root@docker ~]#
5提交自己的鏡像
[root@docker ~]# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
dd90b084d152 ubuntu:latest "/bin/bash" About a minute ago Up About a minute ubuntu_vim
ccb457c15659 mysql:5.6 "docker-entrypoint.s…" 49 minutes ago Exited (1) 49 minutes ago relaxed_bartik
f919fcfcb7b0 hello-world "/hello" 19 hours ago Exited (0) 19 hours ago fervent_benz
a4016a83fc04 hello-world "/hello" 23 hours ago Exited (0) 23 hours ago hopeful_bardeen
f30bd054e899 9c7a54a9a43c "/hello" 40 hours ago Exited (0) 40 hours ago mystifying_shockley
[root@docker ~]# docker commit -m="installed vim" -a="circle" dd90b084d152 cirlce/ubuntu:1.0
sha256:4eac314fbf24dffd018c0682a47044f4108f5fef02d8af5d6a79e91c8bfa0765
[root@docker ~]#
對比
[root@docker ~]# docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
'cirlce/ubuntu' 1.0 4eac314fbf24 2 minutes ago 72.8MB
mysql 5.6 dd3b2a5dcb48 23 months ago 303MB
'ubuntu' latest ba6acccedd29 2 years ago 72.8MB
hello-world latest feb5d9fea6a5 2 years ago 13.3kB
[root@docker ~]#
總結
- Docker中的鏡像分層，支持通過擴展現有鏡像，創建新的鏡像。類似Java繼承于一個Base基礎類，自己再按需擴展。
- 新鏡像是從 base 鏡像一層一層疊加生成的。每安裝一個軟件，就在現有鏡像的基礎上增加一層
