I am a newbie in Docker Technology. Recently I started writing Dockerfiles to deploy web based applications like django-postgres, yii-mariadb etc

When I develop docker files, obviously I do many mistakes and every time I run Dockerfile, it starts installing packages since first line in the new container. Most of the images I use ubuntu:16.04 or centos:6.6 etc. They are fresh one so I need to install many packages inside them. It is very time consuming, if it installs all packages, if I do scripting mistake.

Is there any way if I can run the Dockerfile in existing container where packages are already installed just like when I import new docker image, it does not download every time on docker build, it builds new image from the existing one.

Or any other way which I do not know and it is standard way for dev-ops to write Dockerfile?

Any suggestion is very much appreciated.

Thank you.

yes:
1. you make a Dockerfile using ubuntu:16.04 (for example)
2. you create a new image
3. tag this image like myfirst or similar
4. use this myfirst image to continue, do not need to start over from the beginning, so
use FROM myfirst in the next Dockerfile
5. goto 3

6. finally you can construct a Dockerfile which will do everything from the beginning to the end.