DockerFile----CMD和ENTRYPOINT区别案例

CMD和ENTRYPOINT区别案例

1.使用CMD指令，实现运行容器查当前IP的功能

FROM centos:7

RUN yum -y install curl
CMD ["curl","-s","https://www.cip.cc/"]

[root@aaa ~/mydocker]# docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
mycentos            02                  520e36902f2a        31 seconds ago      290 MB

[root@aaa ~/mydocker]# docker run -it mycentos:02
IP      : 39.90.13.119
地址    : 中国  山东  聊城
运营商  : 联通

如果加个参数“-i”，就会报错

[root@aaa ~/mydocker]# docker run -it mycentos:02 -i
/usr/bin/docker-current: Error response from daemon: oci runtime error: container_linux.go:235: starting container process caused "exec: \"-i\": executable file not found in $PATH".

原因：“-i”参数替换了原来的CMD，而不是添加到原来的curl -s http://www.cip.cc 后面
如果希望加入-i这个参数，就必须输入完整的命令

[root@aaa ~/mydocker]# docker run -it 520e36902f2a curl -s http://www.cip.cc -i
HTTP/1.1 200 OK
Server: openresty
Date: Thu, 06 Aug 2020 13:31:46 GMT
Content-Type: text/html; charset=UTF-8
Transfer-Encoding: chunked
Connection: keep-alive
Vary: Accept-Encoding
X-cip-c: H

IP      : 39.90.13.119
地址    : 中国  山东  聊城
运营商  : 联通

2.使用ENTRYPOINT指令，实现运行容器可以添加参数

#Dockerfile05
FROM centos:7

RUN yum -y install curl
ENTRYPOINT ["curl","-s","https://www.cip.cc/"]

[root@aaa ~/mydocker]# docker build -f Dockerfile05 -t mycentos:03 .
Sending build context to Docker daemon 6.144 kB
Step 1/3 : FROM centos:7
 ---> b5b4d78bc90c
Step 2/3 : RUN yum -y install curl
 ---> Using cache
 ---> db8ecada6a2d
Step 3/3 : ENTRYPOINT curl -s https://www.cip.cc/
 ---> Running in e7f282a2281d
 ---> f79f5093d0ce
Removing intermediate container e7f282a2281d
Successfully built f79f5093d0ce

追加“-i”参数

[root@aaa ~/mydocker]# docker run -it mycentos:03 -i
HTTP/1.1 200 OK
Server: openresty
Date: Thu, 06 Aug 2020 13:36:40 GMT
Content-Type: text/html; charset=UTF-8
Transfer-Encoding: chunked
Connection: keep-alive
Vary: Accept-Encoding
X-cip-c: H

IP      : 39.90.13.119
地址    : 中国  山东  聊城
运营商  : 联通

结论：CMD指令运行容器添加参数会替换CMD的命令；而ENTRYPOINT指令相当于追加参数