理解dockerfile是如何工作的？

1.下面是一个最简单的dockerfile：

FROM baserepoRUN do something

2.这个dockerfile build完等价于下面的命令：

Step 0 : sudo docker pull baserepo:latestsudo docker run --name baserepo_bash01 -i -t baserepo:latest /bin/bashsudo docker ps -ab779269d5001sudo docker commit b779269d5001 imagename01Step 1:sudo docker run --name baserepo_bash02 -i -t imagename01 /bin/bashsudo docker ps -ab779269d5001b779269d5002sudo docker exec -d baserepo_bash02 do somethingsudo docker commit b779269d5002 imagename02sudo docker run --name baserepo_bash -i -t imagename02 /bin/bashsudo docker ps -ab779269d5001b779269d5002b779269d5003sudo docker stop b779269d5002sudo docker rm b779269d5002sudo docker rmi imagename01sudo docker ps -ab779269d5001b779269d5003sudo docker imagesbaserepo:latestimagename02

3.如果看不懂这做的事情，那参照下面的例子理解下

Take the following Dockerfile:FROM baseRUN echo 'foo' > /tmp/foo.txtRUN echo 'bar' >> /tmp/foo.txtand build it:$ docker build --force-rm -t so-26220957 .Sending build context to Docker daemon 3.584 kBSending build context to Docker daemonStep 0 : FROM base ---> b750fe79269dStep 1 : RUN echo 'foo' > /tmp/foo.txt ---> Running in d37d756f6e55 ---> de1d48805de2Removing intermediate container d37d756f6e55Step 2 : RUN echo 'bar' >> /tmp/foo.txt ---> Running in a180fdacd268 ---> 40fd00ee38e1Removing intermediate container a180fdacd268Successfully built 40fd00ee38e1You can now start a new container from b750fe79269d, de1d48805de2 and 40fd00ee38e1:$ docker run --rm b750fe79269d cat /tmp/foo.txtcat: /tmp/foo.txt: No such file or directory$ docker run --rm de1d48805de2 cat /tmp/foo.txtfoo$ docker run --rm 40fd00ee38e1 cat /tmp/foo.txtfoobarof course you might want to start a shell to explore the filesystem and try out commands:$ docker run --rm -it de1d48805de2 bash -ilroot@ecd3ab97cad4:/# ls -l /tmptotal 4-rw-r--r-- 1 root root 4 Oct  6 18:34 foo.txtroot@ecd3ab97cad4:/# cat /tmp/foo.txtfooroot@ecd3ab97cad4:/#来源于：http://stackoverflow.com/questions/26220957/how-can-i-inspect-the-file-system-of-a-failed-docker-build

总结下：dockerfile做的事情其实就是拉镜像，镜像启容器，容器转镜像，镜像再启容器，容器再转镜像，删除中间镜像和容器，大概就是这样的。