09. Docker – Implementation => How to containerize a project | Dockerfile.

Docker – Implementation => How to containerize a project | Dockerfile.

Containerize කිරීමේදී මුලින්ම image එකක් සදා ගත යුතු අතර එයින් අවශ්‍ය පරිදි container instances සදා ගනු ලබයි.

Image එකක් යනු application එකේ සියලුම දේවල් අඩංගු කරලා තියන template එකකි.මෙම template එකෙන් හදන instances තමා containers කියන්නේ.

Basically වම containers යනු image වල runtime instances ලෙසද කිව හැකිය.

Application එකක් containerize කල හැකි ආකාර 2කි.

01.Application එක develop කරලා containerize කරනවා.

02.Container එකක් ඇතුලෙම application එක develop කරනවා.

මෙහිදී පළමු ආකාරය පමණක් විස්තර කරනු ලබයි.

 

01.Application එක develop කරලා containerize කරනවා.

සාමාන්‍ය ලෙස ඕනෙම technology එකක් use කරලා මුලින් application එක develop කරනු ලබන අතර පසුව Dockerfile නම් configuration file එකක් හරහා application එක docker image එකක් බවට convert කරගනු ලබයි.ඉන්පසු docker වලදී එම image එකෙන් ඕන තරම් containers හදාගත හැක.

 

 

Dockerfile

Dockerfile is a text file which include all the instructions to build the docker image. File name can be anything, but most probably take the file name as “Dockerfile”.It is the default file name. If it is changed, that name should be given in image building command.

Docker build command එක දුන්නම layer විදිහටඋඩ සිට පහලට run වේ.එක layer එකක් හෝ fail වුනොත් image එක rebuild කරන්න සිදු වේ.

If docker file name is Dockerfile,

docker build -f Dockerfile -t give_a_name_to_image

But, Because it is the default file name,

docker build . -t give_a_name_to_image

Otherwise

docker build -f abc -t docker_springboot_h2 .                                                                                                                                                                                                                                                                                                                   

මෙම image එකෙන් continers හදාගන්න විදිහ next post එකේදී විස්තර කර ඇත.

 

To take more details about Dockerfile :

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

 

Dockerfile Example

FROM openjdk:11

ARG JAR_FILE=target/docker_SB_3.jar

COPY ${JAR_FILE} app.jar

EXPOSE 8083

ENTRYPOINT ["java","-jar","/app.jar"]

FROM ubuntu

MANAGER lahiru

RUN api-get update && apt-get intall yapache2 && aptget clean

ENV APACHE_RUN_USER www-data

ENV APACHE_RUN_GROUP www-data

EXPOSE 80

# go to user/sbin/apache2 path and run.

CMD [“user/sbin/apache2”,”-D”,”FOREGROUND”]

FROM - The FROM instruction initializes a new build stage and sets the Base Image for subsequent instructions. As such, a valid Dockerfile must start with a FROM instruction

ADD – copping the file from host to the container. It take 2 arguments. Those are source and destination.

ENV – This is used to set environment variable (one or more).These venerable consists of key value pair which can be accessed within the container.

WORKDIR – this is used to set where the command defined with CMD is to be executed.

EXPOSE -This application is active on this port number inside the container. Only specific to the container. This is only used inside the container. If you want to access in from the host machine you have to do port mapping (-p 8080:8080)

MANAGER – this non-executing command declares the author, hence setting the author field of the images. It should come nonetheless after FROM.

USER – is used to set username which is to run the container based on the image being built.(USER 1125)

VOLUME – This is used to enable access from your container to a directory on the host machine.(VOLUME[/lahinu/myfile]).All the file related to the container is stored here. Same path can be shared with multiple containers.