Dockerfile入門

選手一號位發表於2022-04-05

1.Dockerfile介紹

在之前Docker的使用中,我們直接從倉庫下載需要的映象到本地,然後稍加配置就可以應用了,通常從倉庫下載下來的映象都是通用的,無任何私有化的東西,我們拿過來就需要加很多的配置,每次使用就很麻煩。如果我們想定製化某一個映象可以嗎?比如Nginx,我不想每次使用都加很多的配置,而是定製化後,我再按照定製化的規則去使用,及時的安裝部署我需要的Nginx環境。DockerFile就是做這個工作的,一個用基礎映象來構建新映象的文字檔案,裡面包含構建映象需要的各種指令。

1.1 編寫Dockerfile

使用Dockerfile構建Nginx映象,在一個空目錄下建立Dockerfile檔案

[root@hadoop101 nginx]# pwd
/home/docker_test/docker_files/nginx
[root@hadoop101 nginx]# vim Dockerfile
[root@hadoop101 nginx]# ll
total 4
-rw-r--r-- 1 root root 153 Mar 29 23:33 Dockerfile

Dockerfile內容如下:

FROM nginx
​
VOLUME ["volume01","volume02"]
​
RUN echo 'welcome,this is a nginx image of build local.' > /usr/share/nginx/html/index.html
​
RUN echo '----end----'
​
RUN /bin/bash

1.2 構建映象

[root@hadoop101 nginx]# docker build -t zhangbao/nginx001:1.0 .

[root@hadoop101 nginx]# docker build -t zhangbao/nginx001:1.0 .
Sending build context to Docker daemon  2.048kB
Step 1/5 : FROM nginx
 ---> 605c77e624dd
Step 2/5 : VOLUME ["volume01","volume02"]
 ---> Running in d9ff85f068bf
Removing intermediate container d9ff85f068bf
 ---> 801484ddbb09
Step 3/5 : RUN echo '構建本地nginx映象' > /usr/share/nginx/html/index.html
 ---> Running in 6614ebace633
Removing intermediate container 6614ebace633
 ---> 29a385ed17b6
Step 4/5 : RUN echo '----end----'
 ---> Running in 3449cc6cf814
----end----
Removing intermediate container 3449cc6cf814
 ---> 5d6941c830a4
Step 5/5 : RUN /bin/bash
 ---> Running in 1f106444b093
Removing intermediate container 1f106444b093
 ---> 440fd4b943c7
Successfully built 440fd4b943c7
Successfully tagged zhangbao/nginx001:1.0
[root@hadoop101 nginx]#

1.3 執行映象

docker run -d -p 80:80 zhangbao/nginx001:1.0

訪問:http://192.168.88.71/

首頁可以檢視 welcome,this is a nginx image of build local.

2. Dockerfile構建過程

構建一個新映象,我們可以大致分為三個步驟:編寫Dockerfile檔案 > docker build > docker run

2.1 基礎知識

Dockerfile的基礎知識

  1. 每個關鍵字(指令)都必須大寫

  2. 執行過程從上到下,順序執行

  3. #為註釋

  4. 每個指令代表一層,都會建立提交一個新的映象層

Dockerfile指令

FROM            指定基礎映象
MAINTAINER      指定作者
RUN             執行引數中定義的命令,構建映象時需要的命令
EXPOSE          向容器外部公開的埠號
WORKDIR         設定容器內預設工作目錄
USER            指定使用者
ENTROYPOINT     指定一個容器啟動時執行的命令
ENV             設定環境變數
ADD|COPY        複製檔案到映象中
VOLUME          容器資料卷,向映象建立的容器新增捲
CMD             容器啟動時要執行的命令,可以有多個,但只有最後一個生效

2.2 構建過程

Dockerfile的構建過程就是build的執行過程

1.把當前目錄和子目錄當做上下文傳遞給docker服務,命令最後的點表示當前上下文。
2.從當前目錄(不包括子目錄)找到Dockerfile檔案,如果不指定檔案,必須是此檔名。
3.檢查docker語法。
4.從基礎映象執行一個容器。
5.執行指令,修改容器,如上面操作新增資料卷,修改首頁。
6.對修改後的容器提交一個新的映象層,也可叫做中間層映象。
7.針對中間層生成的映象,執行新的容器。
8.重複執行修改容器、提交映象、執行容器指令,直到所有指令執行完成。

注:每條指令都會生成新的映象,也就是生成中間層映象,這樣執行速度其實會很慢,可以不使用快取。在構建命令中加上--no-cache=true 即可。可根據實際場景選擇是否需要快取。

3. 構建一個自己的centos

我們已經熟悉了構建Dockerfile的基礎指令,現在可以做一些基本實踐了。

3.1 執行一個官方centos

首先我們執行一個原生的centos,然後做一些linux的基本操作

[root@hadoop101 ~]# docker run -it centos /bin/bash
[root@a0db59573b95 /]# ls
bin  dev  etc  home  lib  lib64  lost+found  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var
[root@a0db59573b95 /]# ll
bash: ll: command not found
[root@a0db59573b95 /]# vim test
bash: vim: command not found
[root@a0db59573b95 /]# ifconfig
bash: ifconfig: command not found
[root@a0db59573b95 /]#

可以看到,我們已經執行一個centos,然後發現一些基礎的命令是沒有的,這就說明這個contos是一個壓縮版的,如果我們想執行一個有這些命令的映象呢?這就需要在Dockerfile中做一些操作了?

3.2 編寫Dockerfile檔案

記住在一個空白的目錄下建立Dockerfile檔案,我這裡檔名dockerfile-mycentos,內容如下:

FROM centos
#指定作者
MAINTAINER  zhangbao<zhangbaohpu@163.com>
​
ENV MYPATH /usr/local
WORKDIR $MYPATH
​
#下載需要的工具類
RUN yum -y install vim
RUN yum -y install net-tools
​
EXPOSE 80
​
CMD echo "--end--"
CMD /bin/bash

3.3 構建新映象

如果是自定義Dockerfile檔名,則構建時必須指定檔名,否則檔名必須是:Dockerfile

[root@hadoop101 mycentos]# docker build -f dockerfile-mycentos -t mysentos:1.0 .
Sending build context to Docker daemon  2.048kB
Step 1/9 : FROM centos
 ---> 5d0da3dc9764
Step 2/9 : MAINTAINER  zhangbao<zhangbaohpu@163.com>
 ---> Running in d9b4afe40ef6
Removing intermediate container d9b4afe40ef6
 ---> 87e522a4dcb6
Step 3/9 : ENV MYPATH /usr/local
 ---> Running in 2fe975209f1e
Removing intermediate container 2fe975209f1e
 ---> 30491c2e1634
Step 4/9 : WORKDIR $MYPATH
 ---> Running in cd9b1810f244
Removing intermediate container cd9b1810f244
 ---> d2addbefe4f6
Step 5/9 : RUN yum -y install vim
 ---> Running in d6a8caa012e9
CentOS Linux 8 - AppStream                       64  B/s |  38  B     00:00
Error: Failed to download metadata for repo 'appstream': Cannot prepare internal mirrorlist: No URLs in mirrorlist
The command '/bin/sh -c yum -y install vim' returned a non-zero code: 1
[root@hadoop101 mycentos]#

3.4 問題及修復

這時候發現失敗了,查問題是centos8的官方源已經下線了,導致yum下載失敗。那剛好,我們在自定義映象的時候可以修復這些問題。只需修改yum的預設源就可以了,這個操作也放在Dockerfile檔案內。我們修復後Dockerfile檔案如下:

FROM centos
#指定作者
MAINTAINER  zhangbao<zhangbaohpu@163.com>

#ENV kv格式,這裡指定工作目錄,及預設進入容器的目錄
ENV MYPATH /usr/local
WORKDIR $MYPATH

#將原有的yum配置備份下
RUN tar cvf /etc/yum.repos.d.tar /etc/yum.repos.d

#修改yum源配置,
RUN curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-vault-8.5.2111.repo

#刪除掉多於的repo檔案
RUN rm -rf /etc/yum.repos.d/CentOS-Linux-*

#使yum配置更新
RUN yum clean all
RUN yum makecache

#下載需要的工具類
RUN yum -y install vim
RUN yum -y install net-tools

EXPOSE 80

CMD echo "--end--"
CMD /bin/bash

3.5 重新構建映象

重新構建下修改後的Dockerfile檔案

docker build -f dockerfile-mycentos -t mysentos:1.0 .

[root@hadoop101 mycentos]# docker build -f dockerfile-mycentos -t mysentos:1.0 .
Sending build context to Docker daemon   2.56kB
Step 1/14 : FROM centos
 ---> 5d0da3dc9764
Step 2/14 : MAINTAINER  zhangbao<zhangbaohpu@163.com>
 ---> Running in 79ff0ddc554d
Removing intermediate container 79ff0ddc554d
 ---> 0cc1bf4a4ba0
Step 3/14 : ENV MYPATH /usr/local
 ---> Running in 59d3d432c58c
Removing intermediate container 59d3d432c58c
 ---> 839ed1e4b944
Step 4/14 : WORKDIR $MYPATH
 ---> Running in d085e4887d92
Removing intermediate container d085e4887d92
 ---> 41c10774900b
Step 5/14 : RUN tar cvf /etc/yum.repos.d.tar /etc/yum.repos.d
 ---> Running in 1ab58ab850c0
/etc/yum.repos.d/
/etc/yum.repos.d/CentOS-Linux-AppStream.repo
/etc/yum.repos.d/CentOS-Linux-BaseOS.repo
/etc/yum.repos.d/CentOS-Linux-ContinuousRelease.repo
/etc/yum.repos.d/CentOS-Linux-Debuginfo.repo
/etc/yum.repos.d/CentOS-Linux-Devel.repo
/etc/yum.repos.d/CentOS-Linux-Extras.repo
/etc/yum.repos.d/CentOS-Linux-FastTrack.repo
/etc/yum.repos.d/CentOS-Linux-HighAvailability.repo
/etc/yum.repos.d/CentOS-Linux-Media.repo
/etc/yum.repos.d/CentOS-Linux-Plus.repo
/etc/yum.repos.d/CentOS-Linux-PowerTools.repo
/etc/yum.repos.d/CentOS-Linux-Sources.repo
tar: Removing leading `/' from member names
Removing intermediate container 1ab58ab850c0
 ---> bfd1c4cd694c
Step 6/14 : RUN curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-vault-8.5.2111.repo
 ---> Running in 73ebef623f8a
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  2495  100  2495    0     0  12351      0 --:--:-- --:--:-- --:--:-- 12351
Removing intermediate container 73ebef623f8a
 ---> 22812c68f967
Step 7/14 : RUN rm -rf /etc/yum.repos.d/CentOS-Linux-*
 ---> Running in eb8426f499b0
Removing intermediate container eb8426f499b0
 ---> 8dc6bd0b4e84
Step 8/14 : RUN yum clean all
 ---> Running in a508fb503158
0 files removed
Removing intermediate container a508fb503158
 ---> c6831cfda20f
Step 9/14 : RUN yum makecache
 ---> Running in 67c3f0dc0a6a
CentOS-8.5.2111 - Base - mirrors.aliyun.com      16 MB/s | 4.6 MB     00:00
CentOS-8.5.2111 - Extras - mirrors.aliyun.com    45 kB/s |  10 kB     00:00
CentOS-8.5.2111 - AppStream - mirrors.aliyun.co  16 MB/s | 8.4 MB     00:00
Metadata cache created.
Removing intermediate container 67c3f0dc0a6a
 ---> 6ca3b2fbeb13
Step 10/14 : RUN yum -y install vim
 ---> Running in e81b9f1a4705
Last metadata expiration check: 0:00:05 ago on Tue Apr  5 09:35:43 2022.
Dependencies resolved.
================================================================================
 Package             Arch        Version                   Repository      Size
================================================================================
Installing:
 vim-enhanced        x86_64      2:8.0.1763-16.el8         AppStream      1.4 M
Installing dependencies:
 gpm-libs            x86_64      1.20.7-17.el8             AppStream       39 k
 vim-common          x86_64      2:8.0.1763-16.el8         AppStream      6.3 M
 vim-filesystem      noarch      2:8.0.1763-16.el8         AppStream       49 k
 which               x86_64      2.21-16.el8               base            49 k

Transaction Summary
================================================================================
Install  5 Packages

Total download size: 7.8 M
Installed size: 30 M
Downloading Packages:
(1/5): gpm-libs-1.20.7-17.el8.x86_64.rpm        235 kB/s |  39 kB     00:00
(2/5): which-2.21-16.el8.x86_64.rpm             203 kB/s |  49 kB     00:00
(3/5): vim-filesystem-8.0.1763-16.el8.noarch.rp 776 kB/s |  49 kB     00:00
(4/5): vim-common-8.0.1763-16.el8.x86_64.rpm     16 MB/s | 6.3 MB     00:00
(5/5): vim-enhanced-8.0.1763-16.el8.x86_64.rpm  5.4 MB/s | 1.4 MB     00:00
--------------------------------------------------------------------------------
Total                                            19 MB/s | 7.8 MB     00:00
Running transaction check
Transaction check succeeded.
Running transaction test
Transaction test succeeded.
Running transaction
  Preparing        :                                                        1/1
  Installing       : vim-filesystem-2:8.0.1763-16.el8.noarch                1/5
  Installing       : vim-common-2:8.0.1763-16.el8.x86_64                    2/5
  Installing       : gpm-libs-1.20.7-17.el8.x86_64                          3/5
  Running scriptlet: gpm-libs-1.20.7-17.el8.x86_64                          3/5
  Installing       : which-2.21-16.el8.x86_64                               4/5
  Installing       : vim-enhanced-2:8.0.1763-16.el8.x86_64                  5/5
  Running scriptlet: vim-enhanced-2:8.0.1763-16.el8.x86_64                  5/5
  Running scriptlet: vim-common-2:8.0.1763-16.el8.x86_64                    5/5
  Verifying        : which-2.21-16.el8.x86_64                               1/5
  Verifying        : gpm-libs-1.20.7-17.el8.x86_64                          2/5
  Verifying        : vim-common-2:8.0.1763-16.el8.x86_64                    3/5
  Verifying        : vim-enhanced-2:8.0.1763-16.el8.x86_64                  4/5
  Verifying        : vim-filesystem-2:8.0.1763-16.el8.noarch                5/5

Installed:
  gpm-libs-1.20.7-17.el8.x86_64         vim-common-2:8.0.1763-16.el8.x86_64
  vim-enhanced-2:8.0.1763-16.el8.x86_64 vim-filesystem-2:8.0.1763-16.el8.noarch
  which-2.21-16.el8.x86_64

Complete!
Removing intermediate container e81b9f1a4705
 ---> 3d731b0904e6
Step 11/14 : RUN yum -y install net-tools
 ---> Running in f45f6c7c9c8c
Last metadata expiration check: 0:00:17 ago on Tue Apr  5 09:35:43 2022.
Dependencies resolved.
================================================================================
 Package         Architecture Version                          Repository  Size
================================================================================
Installing:
 net-tools       x86_64       2.0-0.52.20160912git.el8         base       322 k

Transaction Summary
================================================================================
Install  1 Package

Total download size: 322 k
Installed size: 942 k
Downloading Packages:
net-tools-2.0-0.52.20160912git.el8.x86_64.rpm   934 kB/s | 322 kB     00:00
--------------------------------------------------------------------------------
Total                                           930 kB/s | 322 kB     00:00
Running transaction check
Transaction check succeeded.
Running transaction test
Transaction test succeeded.
Running transaction
  Preparing        :                                                        1/1
  Installing       : net-tools-2.0-0.52.20160912git.el8.x86_64              1/1
  Running scriptlet: net-tools-2.0-0.52.20160912git.el8.x86_64              1/1
  Verifying        : net-tools-2.0-0.52.20160912git.el8.x86_64              1/1

Installed:
  net-tools-2.0-0.52.20160912git.el8.x86_64

Complete!
Removing intermediate container f45f6c7c9c8c
 ---> adc0f183e07e
Step 12/14 : EXPOSE 80
 ---> Running in 9422041e18c2
Removing intermediate container 9422041e18c2
 ---> e94ae254891f
Step 13/14 : CMD echo "--end--"
 ---> Running in 9183b6a1444d
Removing intermediate container 9183b6a1444d
 ---> c3978bb3cb17
Step 14/14 : CMD /bin/bash
 ---> Running in 536c8de964d3
Removing intermediate container 536c8de964d3
 ---> 68f0ddc7c99f
Successfully built 68f0ddc7c99f
Successfully tagged mysentos:1.0
[root@hadoop101 mycentos]#

總共分為14步,即每個指令一步,也表示每一步算一層。整個構建過程還是很詳細的。

3.6 執行自定義映象

自定義映象已經構建完成,下面我們開始執行映象,並檢測下基礎命令

[root@hadoop101 mycentos]# docker run -it mysentos:1.0
[root@2f70cc22b493 local]# pwd
/usr/local
[root@2f70cc22b493 local]# ll
bash: ll: command not found
[root@2f70cc22b493 local]# vim test
[root@2f70cc22b493 local]# ifconfig
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 172.17.0.2  netmask 255.255.0.0  broadcast 172.17.255.255
        ether 02:42:ac:11:00:02  txqueuelen 0  (Ethernet)
        RX packets 8  bytes 656 (656.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

[root@2f70cc22b493 local]#

可以看到 vimifconfig 命令已經可以使用,ll 命令還需要下載對應的工具包,這裡就不在下載了。

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