1.Docker进阶：存储驱动overlay2

深藏阁楼爱情的钟 2022-12-13 04:18 317阅读 0赞

# 1.overlay2存储驱动架构图 #

![image][]

# 2.概念介绍 #

*  当需要修改一个文件时，使用cow(copy-on\_write，写时拷贝)将文件从只读属性的Lower复制到读写属性的Upper进行修改，结果也保存在Upper层
 *  在Docker中，底下的只读层就是Image，可写层就是Container
 *  如上图所示，当我们在容器中访问（包括增删改查操作）某个文件时，如果在UpperDir中（即容器层）访问不到，就去LowerDir（即镜像层）访问，如果LowerDir和UpperDir中都有，那么UpperDir会覆盖LowerDir中的文件，从而被优先访问

<table> 
 <thead> 
  <tr> 
   <th>概念</th> 
   <th>介绍</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>LowerDir</td> 
   <td>镜像层，只读</td> 
  </tr> 
  <tr> 
   <td>UpperDir</td> 
   <td>容器层，可读可写</td> 
  </tr> 
  <tr> 
   <td>MergedDir</td> 
   <td>LowerDir和UpperDir的合集，作为视图层</td> 
  </tr> 
 </tbody> 
</table>

`初看上面的内容肯定会不理解，没关系，请跟着下面的实例演示操作一遍。`

# 3.实例演示 #

`该实例默认在已安装docker环境下操作，如未安装，请先安装docker环境`

[1.Docker入门：什么是Docker？如何安装Docker？][1.Docker_Docker_Docker]

## step.1 查看overlay2的镜像结构 ##

# 进入/var/lib/docker/overlay2
    [root@iz2ze78arq0qlz2ldzoxk3z docker]# cd /var/lib/docker/overlay2/
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]#
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]# ll
    total 4
    drwx------ 2 root root 4096 Oct  9 17:38 l
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]#

## step.2 下载nginx镜像，并运行nginx容器 ##

# 下载并以后台的方式启动nginx，起名为nginx-1，设置公网访问为3344，设置启动占用端口为80
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]# docker run -d --name nginx-1 -p 3344:80 nginx
    Unable to find image 'nginx:latest' locally
    latest: Pulling from library/nginx
    d121f8d1c412: Pull complete
    66a200539fd6: Pull complete
    e9738820db15: Pull complete
    d74ea5811e8a: Pull complete
    ffdacbba6928: Pull complete
    Digest: sha256:fc66cdef5ca33809823182c9c5d72ea86fd2cef7713cf3363e1a0b12a5d77500
    Status: Downloaded newer image for nginx:latest
    b46631088793c232075fb5020963a1f6bb455de2113896534f56e670c35c5d7f
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]# docker ps
    CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                  NAMES
    b46631088793        nginx               "/docker-entrypoint.…"   37 seconds ago      Up 37 seconds       0.0.0.0:3344->80/tcp   nginx-1
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]#

## step.3 再次查看overlay2的目录结构 ##

[root@iz2ze78arq0qlz2ldzoxk3z overlay2]# ll
    total 32
    drwx------ 4 root root 4096 Oct  9 17:40 0772590e61adc3bde67511a9ebe3ecc087aca8e8e2f8071c46c584d79116342b
    drwx------ 3 root root 4096 Oct  9 17:40 2332b96407caa708d39dd4dd8baf5ee477c451ae7ffe86346825807a25fc4192
    drwx------ 4 root root 4096 Oct  9 17:40 2350cc6a94b0bd0edc875315895a5a07be5bb6b2019f211d09f50703a55394fd
    drwx------ 5 root root 4096 Oct  9 17:40 5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5
    drwx------ 4 root root 4096 Oct  9 17:40 5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5-init
    drwx------ 4 root root 4096 Oct  9 17:40 856c994fa5ee5ceb2443634d5e0d5648c5444fa439eaa0ee1b9e4bda16149a28
    drwx------ 4 root root 4096 Oct  9 17:40 9f1d6ac61af19429182c93cff9c0b5973d8604f00f69dc0e9a45895d0df5fb6e
    drwx------ 2 root root 4096 Oct  9 17:40 l
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]#

## step.4 查看nginx镜像的详细信息 ##

# 查看nginx的镜像详细信息，992e3b7be046是下载的nginx的镜像Id，可以通过docker images获取
    docker inspect 992e3b7be046
    
    # 由于篇幅有限，只列出部分内容，其中我们着重关注GraphDriver
    [
        { 
            ... ...
            "GraphDriver": { 
                "Data": { 
                    "LowerDir": "/var/lib/docker/overlay2/2350cc6a94b0bd0edc875315895a5a07be5bb6b2019f211d09f50703a55394fd/diff:/var/lib/docker/overlay2/856c994fa5ee5ceb2443634d5e0d5648c5444fa439eaa0ee1b9e4bda16149a28/diff:/var/lib/docker/overlay2/0772590e61adc3bde67511a9ebe3ecc087aca8e8e2f8071c46c584d79116342b/diff:/var/lib/docker/overlay2/2332b96407caa708d39dd4dd8baf5ee477c451ae7ffe86346825807a25fc4192/diff",
                    "MergedDir": "/var/lib/docker/overlay2/9f1d6ac61af19429182c93cff9c0b5973d8604f00f69dc0e9a45895d0df5fb6e/merged",
                    "UpperDir": "/var/lib/docker/overlay2/9f1d6ac61af19429182c93cff9c0b5973d8604f00f69dc0e9a45895d0df5fb6e/diff",
                    "WorkDir": "/var/lib/docker/overlay2/9f1d6ac61af19429182c93cff9c0b5973d8604f00f69dc0e9a45895d0df5fb6e/work"
                },
                "Name": "overlay2"
            }
            ... ...
        }
    ]

# 为了方便观看，我们把这些目录路径分行列举出来
    【LowerDir】
    /var/lib/docker/overlay2/2350cc6a94b0bd0edc875315895a5a07be5bb6b2019f211d09f50703a55394fd/diff
    /var/lib/docker/overlay2/856c994fa5ee5ceb2443634d5e0d5648c5444fa439eaa0ee1b9e4bda16149a28/diff
    /var/lib/docker/overlay2/0772590e61adc3bde67511a9ebe3ecc087aca8e8e2f8071c46c584d79116342b/diff
    /var/lib/docker/overlay2/2332b96407caa708d39dd4dd8baf5ee477c451ae7ffe86346825807a25fc4192/diff
    
    【UpperDir】
    /var/lib/docker/overlay2/9f1d6ac61af19429182c93cff9c0b5973d8604f00f69dc0e9a45895d0df5fb6e/diff
    
    【MergedDir】
    /var/lib/docker/overlay2/9f1d6ac61af19429182c93cff9c0b5973d8604f00f69dc0e9a45895d0df5fb6e/merged
    
    【WorkDir】
    /var/lib/docker/overlay2/9f1d6ac61af19429182c93cff9c0b5973d8604f00f69dc0e9a45895d0df5fb6e/work
    
    # 为了方便对比，我们再把overlay2目录下的内容列出来
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]# ll
    total 32
    drwx------ 4 root root 4096 Oct  9 17:40 0772590e61adc3bde67511a9ebe3ecc087aca8e8e2f8071c46c584d79116342b
    drwx------ 3 root root 4096 Oct  9 17:40 2332b96407caa708d39dd4dd8baf5ee477c451ae7ffe86346825807a25fc4192
    drwx------ 4 root root 4096 Oct  9 17:40 2350cc6a94b0bd0edc875315895a5a07be5bb6b2019f211d09f50703a55394fd
    drwx------ 5 root root 4096 Oct  9 17:40 5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5
    drwx------ 4 root root 4096 Oct  9 17:40 5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5-init
    drwx------ 4 root root 4096 Oct  9 17:40 856c994fa5ee5ceb2443634d5e0d5648c5444fa439eaa0ee1b9e4bda16149a28
    drwx------ 4 root root 4096 Oct  9 17:40 9f1d6ac61af19429182c93cff9c0b5973d8604f00f69dc0e9a45895d0df5fb6e
    drwx------ 2 root root 4096 Oct  9 17:40 l
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]#

`可以看到，当前overlay2目录下除了`

5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5
    5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5-init

`这个两个目录以外，其他目录都能一一对应nginx镜像的LowerDir、UpperDir、MergedDir、WorkDir的前缀，多出来的这两个目录我们放到后面说，可以先提一下的是这两个目录是nginx容器对应的目录。`

## step.5 查看nginx镜像层结构 ##

`nginx镜像层的LowerDir中的目录从上往下越来越底层，最底层2232b96是centos层，0772590是nginx层，我们以nginx层为例来查看镜像层结构`

# 在此之前先查看一下软链接目录的内容，我们列举出来，方便后面对比
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]# ll l/
    total 28
    lrwxrwxrwx 1 root root 72 Oct  9 17:40 25M3DGCRDJ3JGEGYYO6FOUGS6N -> ../2350cc6a94b0bd0edc875315895a5a07be5bb6b2019f211d09f50703a55394fd/diff
    lrwxrwxrwx 1 root root 72 Oct  9 17:40 BWR6CCYRZHPZGWV5PJA56ZQCZX -> ../856c994fa5ee5ceb2443634d5e0d5648c5444fa439eaa0ee1b9e4bda16149a28/diff
    lrwxrwxrwx 1 root root 72 Oct  9 17:40 DYRJLUUELXIXC3AOLOHHNBUNTW -> ../0772590e61adc3bde67511a9ebe3ecc087aca8e8e2f8071c46c584d79116342b/diff
    lrwxrwxrwx 1 root root 72 Oct  9 17:40 GGBFM2XRVEIMSKUL6YZW2LAIDA -> ../9f1d6ac61af19429182c93cff9c0b5973d8604f00f69dc0e9a45895d0df5fb6e/diff
    lrwxrwxrwx 1 root root 72 Oct  9 17:40 LOA76ZICCXWTAYB7FP4L5HKOPW -> ../2332b96407caa708d39dd4dd8baf5ee477c451ae7ffe86346825807a25fc4192/diff
    lrwxrwxrwx 1 root root 77 Oct  9 17:40 TY2VIEJBHC6N7YJULFALY635MT -> ../5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5-init/diff
    lrwxrwxrwx 1 root root 72 Oct  9 17:40 Y2LEYQL6SK6TKJFUATQYSHMBWX -> ../5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5/diff
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]#
    
    # 进入nginx镜像层
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]# cd 0772590e61adc3bde67511a9ebe3ecc087aca8e8e2f8071c46c584d79116342b
    [root@iz2ze78arq0qlz2ldzoxk3z 0772590e61adc3bde67511a9ebe3ecc087aca8e8e2f8071c46c584d79116342b]# ll
    total 16
    -rw------- 1 root root    0 Oct  9 17:40 committed
    drwxr-xr-x 8 root root 4096 Oct  9 17:40 diff
    -rw-r--r-- 1 root root   26 Oct  9 17:40 link
    -rw-r--r-- 1 root root   28 Oct  9 17:40 lower
    drwx------ 2 root root 4096 Oct  9 17:40 work
    
    # 查看link文件的内容
    [root@iz2ze78arq0qlz2ldzoxk3z 0772590e61adc3bde67511a9ebe3ecc087aca8e8e2f8071c46c584d79116342b]# cat link
    DYRJLUUELXIXC3AOLOHHNBUNTW
    [root@iz2ze78arq0qlz2ldzoxk3z 0772590e61adc3bde67511a9ebe3ecc087aca8e8e2f8071c46c584d79116342b]#
    # 可以发现这与overlay2目录中的软链接目录 l 内记录的关系一致
    
    # 查看lower文件内容
    [root@iz2ze78arq0qlz2ldzoxk3z 0772590e61adc3bde67511a9ebe3ecc087aca8e8e2f8071c46c584d79116342b]# cat lower
    l/LOA76ZICCXWTAYB7FP4L5HKOPW
    [root@iz2ze78arq0qlz2ldzoxk3z 0772590e61adc3bde67511a9ebe3ecc087aca8e8e2f8071c46c584d79116342b]#
    # 可以发现lower也对应软链接目录 l 内的某一个软链接，根据对比可知，该软链接对应的目录是
    LOA76ZICCXWTAYB7FP4L5HKOPW -> ../2332b96407caa708d39dd4dd8baf5ee477c451ae7ffe86346825807a25fc4192/diff
    
    # 我们再看一下nginx镜像的LowerDir目录内容
    【LowerDir】
    /var/lib/docker/overlay2/2350cc6a94b0bd0edc875315895a5a07be5bb6b2019f211d09f50703a55394fd/diff
    /var/lib/docker/overlay2/856c994fa5ee5ceb2443634d5e0d5648c5444fa439eaa0ee1b9e4bda16149a28/diff
    /var/lib/docker/overlay2/0772590e61adc3bde67511a9ebe3ecc087aca8e8e2f8071c46c584d79116342b/diff
    /var/lib/docker/overlay2/2332b96407caa708d39dd4dd8baf5ee477c451ae7ffe86346825807a25fc4192/diff
    # 可以发现，2332b96是LowerDir中的最底层，即centos镜像层，因此当前目录中的lower文件软链接的是当前镜像层（nginx镜像层）的上一层（从文中列举的顺序来说是最底层）
    
    # 进入diff目录查看
    [root@iz2ze78arq0qlz2ldzoxk3z 0772590e61adc3bde67511a9ebe3ecc087aca8e8e2f8071c46c584d79116342b]# cd diff/
    [root@iz2ze78arq0qlz2ldzoxk3z diff]# ll
    total 24
    drwxr-xr-x  2 root root 4096 Oct  6 06:44 docker-entrypoint.d
    drwxr-xr-x 20 root root 4096 Oct  6 06:44 etc
    drwxr-xr-x  5 root root 4096 Oct  6 06:44 lib
    drwxrwxrwt  2 root root 4096 Oct  6 06:44 tmp
    drwxr-xr-x  7 root root 4096 Sep  8 15:00 usr
    drwxr-xr-x  5 root root 4096 Sep  8 15:00 var
    [root@iz2ze78arq0qlz2ldzoxk3z diff]# cd usr/share/
    [root@iz2ze78arq0qlz2ldzoxk3z share]# ll
    total 52
    drwxr-xr-x  2 root root 4096 Oct  6 06:44 bug
    drwxr-xr-x  3 root root 4096 Oct  6 06:44 ca-certificates
    drwxr-xr-x 53 root root 4096 Oct  6 06:44 doc
    drwxr-xr-x  2 root root 4096 Oct  6 06:44 doc-base
    drwxr-xr-x  3 root root 4096 Oct  6 06:44 fontconfig
    drwxr-xr-x  3 root root 4096 Oct  6 06:44 fonts
    drwxr-xr-x  2 root root 4096 Oct  6 06:44 java
    drwxr-xr-x  3 root root 4096 Oct  6 06:44 nginx
    drwxr-xr-x  2 root root 4096 Oct  6 06:44 readline
    drwxr-xr-x  3 root root 4096 Oct  6 06:44 sensible-utils
    drwxr-xr-x  3 root root 4096 Oct  6 06:44 X11
    drwxr-xr-x  3 root root 4096 Oct  6 06:44 xml
    drwxr-xr-x  3 root root 4096 Oct  6 06:44 zsh
    [root@iz2ze78arq0qlz2ldzoxk3z share]# tree nginx/
    nginx/
    └── html
        ├── 50x.html
        └── index.html
    
    1 directory, 2 files
    [root@iz2ze78arq0qlz2ldzoxk3z share]#
    # 根据这些目录结构可以证明这里是nginx镜像层

`镜像层目录结构内容：`

<table> 
 <thead> 
  <tr> 
   <th>组成部分</th> 
   <th>说明</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>committed</td> 
   <td>制作镜像时的commit内容，不重要</td> 
  </tr> 
  <tr> 
   <td>diff</td> 
   <td>记录每一层自己内容的数据，顾名思义，diff，不同，代表当前层与上一层的不同内容</td> 
  </tr> 
  <tr> 
   <td>link</td> 
   <td>记录该层链接目录（实际是l目录中的某个链接）</td> 
  </tr> 
  <tr> 
   <td>lower</td> 
   <td>记录该层的上一层链接</td> 
  </tr> 
  <tr> 
   <td>work</td> 
   <td>写时拷贝发生时才使用它，可以理解成专门给写时拷贝场景提供的目录</td> 
  </tr> 
 </tbody> 
</table>

## step.6 回过头再看overlay2目录结构 ##

# 进入/var/lib/docker/overlay2
    [root@iz2ze78arq0qlz2ldzoxk3z share]# cd /var/lib/docker/overlay2
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]# ll
    total 32
    drwx------ 4 root root 4096 Oct  9 17:40 0772590e61adc3bde67511a9ebe3ecc087aca8e8e2f8071c46c584d79116342b
    drwx------ 3 root root 4096 Oct  9 17:40 2332b96407caa708d39dd4dd8baf5ee477c451ae7ffe86346825807a25fc4192
    drwx------ 4 root root 4096 Oct  9 17:40 2350cc6a94b0bd0edc875315895a5a07be5bb6b2019f211d09f50703a55394fd
    drwx------ 5 root root 4096 Oct  9 17:40 5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5
    drwx------ 4 root root 4096 Oct  9 17:40 5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5-init
    drwx------ 4 root root 4096 Oct  9 17:40 856c994fa5ee5ceb2443634d5e0d5648c5444fa439eaa0ee1b9e4bda16149a28
    drwx------ 4 root root 4096 Oct  9 17:40 9f1d6ac61af19429182c93cff9c0b5973d8604f00f69dc0e9a45895d0df5fb6e
    drwx------ 2 root root 4096 Oct  9 17:40 l
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]#
    
    # 查看完nginx镜像层的目录内容（对应的是0772590），再看看其他目录的结构
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]# ll 2350cc6a94b0bd0edc875315895a5a07be5bb6b2019f211d09f50703a55394fd
    total 16
    -rw------- 1 root root    0 Oct  9 17:40 committed
    drwxr-xr-x 3 root root 4096 Oct  9 17:40 diff
    -rw-r--r-- 1 root root   26 Oct  9 17:40 link
    -rw-r--r-- 1 root root   86 Oct  9 17:40 lower
    drwx------ 2 root root 4096 Oct  9 17:40 work
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]# ll 9f1d6ac61af19429182c93cff9c0b5973d8604f00f69dc0e9a45895d0df5fb6e
    total 16
    -rw------- 1 root root    0 Oct  9 17:40 committed
    drwxr-xr-x 3 root root 4096 Oct  9 17:40 diff
    -rw-r--r-- 1 root root   26 Oct  9 17:40 link
    -rw-r--r-- 1 root root  115 Oct  9 17:40 lower
    drwx------ 2 root root 4096 Oct  9 17:40 work
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]# 
    # 可以看到其他镜像层跟nginx镜像层目录结构都一样
    
    # 但是有一个例外，centos镜像层，即所有镜像都包括的最底层
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]# ll 2332b96407caa708d39dd4dd8baf5ee477c451ae7ffe86346825807a25fc4192/
    total 8
    -rw-------  1 root root    0 Oct  9 17:40 committed
    drwxr-xr-x 21 root root 4096 Oct  9 17:40 diff
    -rw-r--r--  1 root root   26 Oct  9 17:40 link
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]#
    # 可以发现centos镜像层，即最底层，是没有lower和work的，这是因为centos镜像层作为最底层，是没有上一层的，也不允许写时拷贝操作（根本原因是不允许写操作）

## step.7 查看nginx容器的详细信息 ##

# 查看nginx的镜像详细信息，b46631088793是下载的nginx的镜像Id，可以通过docker ps获取
    docker inspect b46631088793
    
    # 由于篇幅有限，只列出部分内容，其中我们着重关注GraphDriver
    [
        { 
            ... ...
            "GraphDriver": { 
                "Data": { 
                    "LowerDir": "/var/lib/docker/overlay2/5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5-init/diff:/var/lib/docker/overlay2/9f1d6ac61af19429182c93cff9c0b5973d8604f00f69dc0e9a45895d0df5fb6e/diff:/var/lib/docker/overlay2/2350cc6a94b0bd0edc875315895a5a07be5bb6b2019f211d09f50703a55394fd/diff:/var/lib/docker/overlay2/856c994fa5ee5ceb2443634d5e0d5648c5444fa439eaa0ee1b9e4bda16149a28/diff:/var/lib/docker/overlay2/0772590e61adc3bde67511a9ebe3ecc087aca8e8e2f8071c46c584d79116342b/diff:/var/lib/docker/overlay2/2332b96407caa708d39dd4dd8baf5ee477c451ae7ffe86346825807a25fc4192/diff",
                    "MergedDir": "/var/lib/docker/overlay2/5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5/merged",
                    "UpperDir": "/var/lib/docker/overlay2/5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5/diff",
                    "WorkDir": "/var/lib/docker/overlay2/5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5/work"
                },
                "Name": "overlay2"
            }
            ... ...
        }
    ]

# 为了方便观看，我们把这些目录路径分行列出来
    【LowerDir】
    /var/lib/docker/overlay2/5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5-init/diff
    /var/lib/docker/overlay2/9f1d6ac61af19429182c93cff9c0b5973d8604f00f69dc0e9a45895d0df5fb6e/diff
    /var/lib/docker/overlay2/2350cc6a94b0bd0edc875315895a5a07be5bb6b2019f211d09f50703a55394fd/diff
    /var/lib/docker/overlay2/856c994fa5ee5ceb2443634d5e0d5648c5444fa439eaa0ee1b9e4bda16149a28/diff
    /var/lib/docker/overlay2/0772590e61adc3bde67511a9ebe3ecc087aca8e8e2f8071c46c584d79116342b/diff
    /var/lib/docker/overlay2/2332b96407caa708d39dd4dd8baf5ee477c451ae7ffe86346825807a25fc4192/diff
    
    【UpperDir】
    /var/lib/docker/overlay2/5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5/diff
    
    【MergedDir】
    /var/lib/docker/overlay2/5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5/merged
    
    【WorkDir】
    /var/lib/docker/overlay2/5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5/work
    
    # 为了方便对比，我们再把nginx镜像的LowerDir内容列出来
    /var/lib/docker/overlay2/2350cc6a94b0bd0edc875315895a5a07be5bb6b2019f211d09f50703a55394fd/diff
    /var/lib/docker/overlay2/856c994fa5ee5ceb2443634d5e0d5648c5444fa439eaa0ee1b9e4bda16149a28/diff
    /var/lib/docker/overlay2/0772590e61adc3bde67511a9ebe3ecc087aca8e8e2f8071c46c584d79116342b/diff
    /var/lib/docker/overlay2/2332b96407caa708d39dd4dd8baf5ee477c451ae7ffe86346825807a25fc4192/diff
    
    # 可以发现nginx容器中的LowerDir内容比nginx镜像的LowerDir多出了这两个目录
    /var/lib/docker/overlay2/5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5-init/diff
    /var/lib/docker/overlay2/9f1d6ac61af19429182c93cff9c0b5973d8604f00f69dc0e9a45895d0df5fb6e/diff
    
    其中
    /var/lib/docker/overlay2/9f1d6ac61af19429182c93cff9c0b5973d8604f00f69dc0e9a45895d0df5fb6e/diff
    是nginx镜像的UpperDir内容
    
    再看nginx容器的UpperDir内容
    /var/lib/docker/overlay2/5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5/diff

# 为了方便对比，我们再把overlay2目录下的内容列出来
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]# ll
    total 32
    drwx------ 4 root root 4096 Oct  9 17:40 0772590e61adc3bde67511a9ebe3ecc087aca8e8e2f8071c46c584d79116342b
    drwx------ 3 root root 4096 Oct  9 17:40 2332b96407caa708d39dd4dd8baf5ee477c451ae7ffe86346825807a25fc4192
    drwx------ 4 root root 4096 Oct  9 17:40 2350cc6a94b0bd0edc875315895a5a07be5bb6b2019f211d09f50703a55394fd
    drwx------ 5 root root 4096 Oct  9 17:40 5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5
    drwx------ 4 root root 4096 Oct  9 17:40 5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5-init
    drwx------ 4 root root 4096 Oct  9 17:40 856c994fa5ee5ceb2443634d5e0d5648c5444fa439eaa0ee1b9e4bda16149a28
    drwx------ 4 root root 4096 Oct  9 17:40 9f1d6ac61af19429182c93cff9c0b5973d8604f00f69dc0e9a45895d0df5fb6e
    drwx------ 2 root root 4096 Oct  9 17:40 l
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]#

`现在就可以明白5e24293开头的这两个目录是哪来的了，没错，就是nginx容器的目录。`

## step.8 查看nginx容器层结构 ##

# 查看nginx容器的LowerDir中xxx-init目录结构
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]# ll 5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5-init/
    total 16
    -rw------- 1 root root    0 Oct  9 17:40 committed
    drwxr-xr-x 4 root root 4096 Oct  9 17:40 diff
    -rw-r--r-- 1 root root   26 Oct  9 17:40 link
    -rw-r--r-- 1 root root  144 Oct  9 17:40 lower
    drwx------ 3 root root 4096 Oct  9 17:40 work
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]#
    # 可以看到与其他镜像层目录内容一致
    
    # 查看nginx容器的UpperDir目录结构
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]# ll 5e24293506344c5595d886a3194b95ca3ddf34e5cf1b1566db796be4567a8de5
    total 20
    drwxr-xr-x 6 root root 4096 Oct  9 17:40 diff
    -rw-r--r-- 1 root root   26 Oct  9 17:40 link
    -rw-r--r-- 1 root root  173 Oct  9 17:40 lower
    drwxr-xr-x 1 root root 4096 Oct  9 17:40 merged
    drwx------ 3 root root 4096 Oct  9 17:40 work
    [root@iz2ze78arq0qlz2ldzoxk3z overlay2]#
    # 可以看到多了一个merged目录，少了一个committed文件

`容器层目录结构内容：`

<table> 
 <thead> 
  <tr> 
   <th>组成部分</th> 
   <th>说明</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>diff</td> 
   <td>记录每一层自己内容的数据，顾名思义，diff，不同，代表当前层与上一层的不同内容</td> 
  </tr> 
  <tr> 
   <td>link</td> 
   <td>记录该层链接目录（实际是l目录中的某个链接）</td> 
  </tr> 
  <tr> 
   <td>lower</td> 
   <td>记录该层的上一层链接</td> 
  </tr> 
  <tr> 
   <td>merged</td> 
   <td>LowerDir与UpperDir的合集，merged作为视图层，它对应的是MergedDir，因此镜像是没有该目录的，只有容器才有，我们使用docker inspect [image_id]能看到镜像也有MergedDir是因为它固定展示格式，实际上并不存在</td> 
  </tr> 
  <tr> 
   <td>work</td> 
   <td>写时拷贝发生时才使用它，可以理解成专门给写时拷贝场景提供的目录</td> 
  </tr> 
 </tbody> 
</table>

## step.9 总结 ##

`overlay2目录包括三部分内容：`

1.  每个镜像层对应的目录文件
2.  每个容器层对应的目录文件
3.  l 软链接目录，记录每个镜像层目录的软链关系

`至此，请在回过头看文章开头的架构图和概念介绍，应该就能理解了。`

[image]: /images/20221123/0e6accf78e41490189f71087d64c8306.png
[1.Docker_Docker_Docker]: https://blog.csdn.net/w_y_x_y/article/details/107797739