Removing what was added in previous layer in docker

Question

I'm trying to reduce the size of my docker image. In my docker file, I do this:

FROM crystal/centos
MAINTAINER crystal

ADD ./rpms/test.rpm ./rpms/ 
RUN yum -y --nogpgcheck localinstall /rpms/test.rpm 

from what I understand, the ADD command is in its own layer, and then RUN is in another layer. So after I install the rpm, how do I go about deleting the initial /rpms directory.

Answer 1

use this technique

RUN curl http://someaddress/test.rpm &&\
    yum -y --nogpgcheck localinstall /rpms/test.rpm &&\
    rm test.rpm