Docker Foundation (4)-- Dockerfile Writing
There are two ways to create images in Docker:
1. Container-based mirroring:
docker commit …
2. Making mirror images based on Dockerfile;
docker build …
Dockerfile production steps:
1. Create a directory;
2. Create a capitalized file in the directory for docker build to identify;
3. Because the execution environment of Dockerfile is in the directory created, you can create a corresponding file for Dockerfile to use;
ex：
[root@master ~]# ls docimageDockerfile index.html [root@master ~]# cat docimage/DockerfileFROM busybox:latest LABEL maintainer="hevttc" ENV DOC_ROOT="/tmp/" \ VOLUME_ROOT="/data/mydata" \ ARGU="/usr/sbin/" COPY index.html /tmp/ VOLUME ${VOLUME_ROOT} RUN ifconfig -a && \ cat ${DOC_ROOT}index.html
Dockerfile format:
Dockerfile Format
The line beginning with "#" is a comment line (multiple lines, anywhere);
INSTRUCTION arguments
Instructions and corresponding parameters, it is recommended that instructions be capitalized, parameters be lowercase, default case can be;
Can be completed with one line of instructions, try not to use multiple lines of instructions;
The first executable instruction must be a FROM instruction;
Docker is to execute the contents of Dockerfile in sequence, pay attention to the writing order;
There are several important commands in Dockerfile:
1. FROM (specify base mirror)
FROM |: or
FROM @
: Specifies the name as the base image;
: label of base image, optional, default to latest when omitted;
2. LABEL (write creator information of current Dockerfile);
LABEL = = = …
3. COPY (copy host files to mirror);
COPY …or COPY ["",... "" ]
: The source file or directory to copy. Wildcards are supported.
: Target path, i.e. file system path of image being created; absolute path is recommended, otherwise, COPY specifies WORKDIR as its starting path;
Note: When there are white space characters in the path, the second format is usually used;
ADD (similar to COPY command, support TAR file and URL path);
ADD …or ADD ["",... "" ]
Note:
If URL does not end with "/", the specified file will be downloaded and created directly as; if URL ends with "/", the file specified by filename URL will be downloaded and saved as/;
If it is a tar file in compressed format on the local system, it will be expanded into a directory, which behaves like the "tar -x" command; however, tar files retrieved via URL will not be expanded automatically;
If there is more than one, or it uses wildcards indirectly or directly, it must be a directory path ending with "/"; if it does not end with "/", it is treated as a normal file and the contents of will be written directly to;
WORKDIR (used to specify the working directory for all RUN, CMD, ENTRYPOINT, COPY and ADD in Dockerfile;);
WORKDIR
WORKDIR can occur multiple times in a Dockerfile, and its path can be relative, but relative to the path specified by the previous WORKDIR directive;
In addition, WORKDIR can also call variables defined by ENV;
VOLUME (used to create a mount point directory in image, which can be used to mount volumes on Docker Host);
VOLUME or VOLUME ["mountpoint"]
Personally, it is not recommended to use: this is Docker daemon to create managed volumes, not binding mounts;
7. EXPOSE (open the port to be listened to for the container, and realize communication with the outside);
EXPOSE [/] [/] [/] …
Used to specify the transport layer protocol, which can be either TCP or UDP, and the default is TCP;
ENV (defines environment variables for mirroring, can be called by other instructions, build_time and run_time can be used);
ENV or ENV =...
Call format:
$variable_name or ${variable_name}
9. ARG (variable used in creating mirror is build_time, generally ARG is used to write version number and author);
ARG [=]
10.RUN (used to specify the program to run during Docker build);
RUN or
RUN ["","","",...] (json array)
CMD (similar to RUN command, executed at run_time);
CMD
CMD ["","","",...] or
CMD ["","",...] (Provides default parameters for ENTRYPOINT directive)
12. ENTRYPOINT (similar to CMD command)
ENTRYPOINT
ENTRYPOINT ["","","",...]
[root@master ~]# cat docimage1/entrypoint.sh#!/ bin/sh exec $@[root@master ~]# cat docimage1/DockerfileFROM nginx:1.14-alpine COPY entrypoint.sh ["/usr/local/nginx","-g","daemon off;"] ENTRYPOINT ["/bin/entrypoint.sh"][root@master ~]# ll docimage1/total usage 8-rw-r-r- 1 root 129 November 1 20:42 Dockerfile-rwxr-xr-x 1 root 19 November 1 20:16 entrypoint.sh
command execution diagram
Create a Dockerfile;
[root@www ~]# mkdir docimage[root@www ~]# vim docimage/Dockerfile[root@www ~]#[root@www ~]# vim docimage/test.txt[root@www ~]# cat docimage/DockerfileFROM nginx:1.14-alpine LABEL maintainer="liujingyu" ENV DOC_ROOT="/tmp" \ VOLUME_ROOT=/data/mydata COPY test.txt ${DOC_ROOT} VOLUME ${VOLUME_ROOT} RUN echo 123 > ${DOC_ROOT}/test.txt CMD cat ${DOC_ROOT}/test.txt[root@www ~]#[root@www ~]# cat docimage/test.txtTHIS is Docker TEST;
Creating Mirrors with Dockerfile:
[root@www ~]# docker build docimage/ -t ljymyy/nginx:v0.2Sending build context to Docker daemon 3.072kBStep 1/7 : FROM nginx:1.14-alpine ---> 77bae8d00654Step 2/7 : LABEL maintainer="liujingyu" ---> Using cache ---> a012ac4c6f51Step 3/7 : ENV DOC_ROOT="/tmp" VOLUME_ROOT=/data/mydata ---> Using cache ---> ee6ed363bfdeStep 4/7 : COPY test.txt ${DOC_ROOT} ---> Using cache ---> a416671fde2aStep 5/7 : VOLUME ${VOLUME_ROOT} ---> Using cache ---> 84bf38b22301Step 6/7 : RUN echo 123 > ${DOC_ROOT}/test.txt ---> Using cache ---> 756cd9857096Step 7/7 : CMD cat ${DOC_ROOT}/test.txt ---> Running in a2f99fcc5fbaRemoving intermediate container a2f99fcc5fba ---> dac468a636e0Successfully built dac468a636e0Successfully tagged ljymyy/nginx:v0.2[root@www ~]# docker image lsREPOSITORY TAG IMAGE ID CREATED SIZEljymyy/nginx v0.2 dac468a636e0 2 minutes ago 17.7MB
Run this image:
[root@www ~]# docker container run --rm --name ngx1 ljymyy/nginx:v0.2123
