How to create custom docker images?

Dockerfile --> used to create our custom images using instructions provided by docker

RHEL9 == Centos9 == Almalinux9

FROM

======

FROM <BASE-OS>:<version>

how to build docker image?

docker build -t <image-name>:<version> . --> Dockerfile

docker build -t <docker-hub-username>/<image-name>:<version> .

docker login -u <username>

docker push <image-name>:<version>

RUN

======

RUN instruction used to install packages, configurations on top of base os. It executes at the time of image building

CMD

======

systemctl will not work in containers.. /etc/systemd/system/*.service

RUN vs CMD

=========

RUN instruction executes at the time of image building

CMD instruction executes at the time of container creation

COPY vs ADD

=========

COPY and ADD both copies the files to images. but ADD has 2 extra capabilities

1. copying from directly from internet to the image

2. extracts tar file directly into image