Docker - centos 7 CMD yum commands run but don't install

Question

I'm fairly new to Docker, and when attempting to install packages via the "Dockerfile" I've noticed that the build steps pass, but when i connect to the docker and load a shell, none of the packages have actually been installed.

Config:

FROM centos:latest
CMD yum -y install epel-release
CMD yum -y install collectd

Build steps:

Sending build context to Docker daemon 40.45 kB
Step 1/3 : FROM centos:latest
---> 67591570dd29
Step 2/3 : CMD yum -y install epel-release
 ---> Using cache
 ---> 4148233bce10
Step 3/3 : CMD yum -y install collectd
---> Using cache
---> 62998bf2ce0f

When connecting to the docker neither package is installed, but I am able to install the packages within the docker:

[root@cassiopeia monitoringDocker]# docker exec -it 0579169abb44 bash
[root@0579169abb44 /]# yum -y install epel-release
Loaded plugins: fastestmirror, ovl
base

Please help!

Answer 1

Use like

FROM centos:latest
RUN \
  yum -y install epel-release && \
  yum -y install collectd

OR

FROM centos:latest
RUN yum -y install epel-release collectd

RUN :

RUN instruction allows you to install your application and packages requited for it. It executes any commands on top of the current image and creates a new layer by committing the results.

CMD :

CMD instruction allows you to set a default command, which will be executed only when you run container without specifying a command. If Docker container runs with a command, the default command will be ignored.