Dockerfile

This labs is about creating image from dockerfile.

mkdir doclab
cd doclab

Create a dockerfile using vi editor
FROM debian:stable
LABEL authors="amit"
RUN apt-get update && apt-get install -y --force-yes apache2
EXPOSE 80

- Save the dockerfile
- docker build -t mydeb .

1. FROM debian:stable: This sets the base image for your Docker image as the official Debian stable image.
2. LABEL authors="amit": This adds a label to your image indicating the author as “amit”. Labels are metadata that can be used to provide information about the image.
3. RUN apt-get update && apt-get install -y --force-yes apache2: This command updates the package list and then installs the Apache2 web server package. The -y flag automatically confirms any prompts during the installation process, and --force-yes is used to force installation without confirmation, which can be risky and is generally not recommended.
4. EXPOSE 80: This instruction indicates that the container will listen on port 80. It’s a declaration of the intended network ports that the container will listen on when running.

docker images
docker inspect <imageid>

 

CMD and ADD example

Create a docker file dockerfileadd

touch file.txt
vi dockerfileadd and copy below code, save it

FROM ubuntu:latest
# Set a working director inside container
WORKDIR /app
#Copy file from current directory
COPY file.txt /app/
#ADD a directory from the host
#ADD /home/lab-user/amit /app/
ADD https://github.com/amitopenwriteup/my_proj/blob/master/k8s-setup.txt /app/
#Till this point copy it in docker file

#below command run in the shell

docker build -t myweb2 -f dockerfileadd .

docker images

docker run  -it <imageid,from image command> /bin/bash
exit

RUN,CMD and ENTRYPOINT 

Lab1

1)mkdir test
cd test
vi date.sh 

//Copy the below code in date.sh

#!/bin/sh
echo `date` $@ >> log.txt;
cat log.txt;

Create a docker file named myimage and copy the below line

FROM alpine
ADD date.sh /
RUN ["/date.sh", "image created"]

docker run myimage cat log.txt
Check the time

If we run the container several times, we’ll see that the date in our
log file doesn’t change. This makes sense because the run step
executes at image build time, not at the container runtime.

Lab2 Create a new docker file named myimage1

FROM alpine
ADD date.sh /
RUN ["/date.sh", "image created"]
CMD ["/date.sh", "container started"]

docker build -t myimage1 .

docker run myimage1

If we run this multiple times, we’ll see that the image created entry
stays the same. But the container started entry updates with every
run. This shows how cmd indeed executes every time the container
starts.

Lab3: create a new dockerfile myimage2 Lets add two cmd commands.

FROM alpine
ADD date.sh /
RUN ["/date.sh", "image created"]
CMD ["/date.sh", "container started"]
CMD ["/date.sh", "container running"]

docker build -t myimage2 .

docker run myimage2

Lab4 : ENTRYPOINT

Create a dockerfile name myimage3

FROM alpine
ADD date.sh /
RUN ["/date.sh", "image created"]
ENTRYPOINT ["/date.sh"]

docker build -t myimage3 .

docker run myimage3 welcome to container