OpenShift 4.10 I: Write Dockerfile, Build, Tag and Push

Dockerfile/Containerfile

There is no docker file syntax man page on RHEL.

https://learn.redhat.com/t5/Containers-DevOps-OpenShift/Is-there-Dockerfile-format-or-example-in-RHEL-man-page-or/td-p/16739

$ sudo dnf provides "*Dockerfile"
Not root, Subscription Management repositories not updated
buildah-tests-1:1.24.2-4.el9_0.x86_64 : Tests for buildah
Repo        : @System
Matched from:
Other       : *Dockerfile

$ rpm -ql buildah-tests | egrep "Dockerfile|Containerfile"
/usr/share/buildah/test/system/bud/add-chmod/Dockerfile
/usr/share/buildah/test/system/bud/add-chmod/Dockerfile.bad
...

Dockerfile instructions	Explenation	Example
FROM	Base image	FROM registry.redhat.io/ubi8/ubi:8.5
MAINTAINER		MAINTAINER Magnus K Karlsson <magnus.k.karlsson@antigo.se>
LABEL	Adds metadata to an image	LABEL com.example.version="0.0.1-beta"
ARG	"Defines a variable that users can pass at build-time to the builder with the docker build command using the --build-arg <varname>=<value> flag."	ARG user1=someuser
ENV	Environment variable <key> to the value <value>	ENV MY_NAME="John Doe" ENV PORT=8080
RUN	RUN dnf install -y httpd
USER	"Use USER to change to a non-root user" "Avoid switching USER back and forth frequently"	USER apache
EXPOSE		EXPOSE ${PORT}
ADD or COPY	"generally speaking, COPY is preferred" ADD is local tar file auto-extraction into the image, as in ADD rootfs.tar.xz /	ADD files.tar.gz ${APACHE_HOME} ADD http://example.com/foobar /
WORKDIR	Set the working directory	WORKDIR ${APACHE_HOME}
VOLUME	Define a volume mount point	VOLUME ${APACHE_HOME}/data
ENTRYPOINT	"set the image’s main command ... then use CMD as the default flags"	ENTRYPOINT ["/usr/sbin/httpd"]
CMD		CMD ["sh", "my-start.sh"]

Reference:

https://docs.docker.com/engine/reference/builder/

https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#dockerfile-instructions

Examples

The order of the instructions is important for USER. First create container user (with specific uid and gid) and then instruct with USER.

After will the instructions be run with the dedicated USER, i.e. later instructions with COPY and ADD, those files will belong to USER.

FROM registry.access.redhat.com/ubi9/ubi
MAINTAINER Magnus K Karlsson <magnus.k.karlsson@antigo.se>
ENV PORT 8080
RUN dnf install -y httpd && \
  sed -i "s/Listen 80/Listen ${PORT}/g" /etc/httpd/conf/httpd.conf && \
  chown -R apache:apache /etc/httpd/logs/ && \
  chown -R apache:apache /run/httpd/
USER apache
EXPOSE ${PORT}
COPY ./index.html /var/www/html
CMD ["httpd", "-D", "FOREGROUND"]

FROM registry.redhat.io/ubi8/ubi:8.5
MAINTAINER Magnus K Karlsson <magnus.k.karlsson@antigo.se>

ARG MYSERVICE_VERSION=1.0.0
ENV MYSERVICE_HOME=/opt/myservice

RUN yum install -y java-1.8.0-openjdk-devel

RUN groupadd -g 2001 myservice && \
  useradd -u 2001 -g 2001 myservice && \
  chown -R myservice:myservice ${MYSERVICE_HOME} && \
  chmod -R 755 ${MYSERVICE_HOME}

USER myservice
EXPOSE 8080

ADD myservice-${MYSERVICE_VERSION}.tar.gz ${MYSERVICE_HOME}
ADD myservice-start.sh ${MYSERVICE_HOME}

WORKDIR ${MYSERVICE_HOME}

VOLUME ${MYSERVICE_HOME}/data

CMD ["sh", "myservice-start.sh"]

Build, Tag and Push

If using official Red Hat repo or other that requires login, you must first login.

$ podman login registry.redhat.io --username you@domain.com

$ podman login quay.io --username you_username

Build, tag and push

$ podman build -t httpd-24-custom:1.0 -f Dockerfile .

$ podman tag localhost/httpd-24-custom quay.io/magnus_k_karlsson/httpd-24-custom:1.0

$ podman push quay.io/magnus_k_karlsson/httpd-24-custom:1.0

Then run