015、调试Dockerfile（2019-01-04 周五）

参考https://www.cnblogs.com/CloudMan6/p/6853329.html

 

Dockerfile构建镜像的过程

 

1、从base镜像运行一个容器

2、执行一条指令，对容器进行修改

3、执行类似 docker commit的操作，生成一个新的镜像层

4、Docker在基于刚刚提交的镜像层运行一个新的容器

5、重复步骤 2-4 ，直到Dockerfile中所有指令执行完毕

 

 

root@docker-lab:~/docker# ls

Dockerfile

root@docker-lab:~/docker# cat Dockerfile

FROM centos

RUN uptime

RUN touch tmpfile

RUN ls /mnt2

root@docker-lab:~/docker# docker build -t centos-t1 .

Sending build context to Docker daemon  2.048kB

Step 1/4 : FROM centos

latest: Pulling from library/centos

a02a4930cb5d: Already exists

Digest: sha256:184e5f35598e333bfa7de10d8fb1cebb5ee4df5bc0f970bf2b1e7c7345136426

Status: Downloaded newer image for centos:latest

---> 1e1148e4cc2c

Step 2/4 : RUN uptime

---> Running in f05e49595929

06:44:46 up 204 days, 22:07,  0 users,  load average: 0.02, 0.02, 0.00

Removing intermediate container f05e49595929

---> be8d26615578

Step 3/4 : RUN touch tmpfile

---> Running in ada319df9d43

Removing intermediate container ada319df9d43

---> acaccd0c45d3

Step 4/4 : RUN ls /mnt2    #    第一次build报错， ls /mnt2 执行失败

---> Running in 590fc8e2360c

ls: cannot access /mnt2: No such file or directory

The command '/bin/sh -c ls /mnt2' returned a non-zero code: 2

root@docker-lab:~/docker# docker build -t centos-t1 .

Sending build context to Docker daemon  2.048kB

Step 1/4 : FROM centos

---> 1e1148e4cc2c    #    第二次build直接使用了之前成功build镜像层的缓存

Step 2/4 : RUN uptime

---> Using cache

---> be8d26615578    #    第二次build直接使用了之前成功build镜像层的缓存

Step 3/4 : RUN touch tmpfile

---> Using cache

---> acaccd0c45d3    #    第二次build直接使用了之前成功build镜像层的缓存

Step 4/4 : RUN ls /mnt2    #    第二次build报错， ls /mnt2 执行失败

---> Running in b17908bf7059

ls: cannot access /mnt2: No such file or directory

The command '/bin/sh -c ls /mnt2' returned a non-zero code: 2

root@docker-lab:~/docker# docker images -a    #    此处可以看到build前三个成功步骤生成的镜像层

REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE

<none>              <none>              be8d26615578        34 seconds ago      202MB

<none>              <none>              acaccd0c45d3        34 seconds ago      202MB

centos              latest              1e1148e4cc2c        4 weeks ago         202MB

root@docker-lab:~/docker# docker run -it acaccd0c45d3    #    进入最后一次成功的镜像层，查看失败原因，没有 /mnt2 目录

[root@9ae841c96c62 /]# ls /mnt2

ls: cannot access /mnt2: No such file or directory

[root@9ae841c96c62 /]# ls /

anaconda-post.log  dev  home  lib64  mnt  proc  run   srv  tmp      usr

bin                etc  lib   media  opt  root  sbin  sys  tmpfile  var

[root@9ae841c96c62 /]#