DevOps Classroom notes 30/Jan/2025

Other Dockerfile Instructions

• LABEL: It adds Metadata to the image
• RUN
• CMD
• EXPOSE: This instructions adds information about the ports of the application
• ARG
• ENV
• ENTRYPOINT
• WORKDIR
• USER: This sets the user to run inside the container. User has to be existing before using this instruction.

Points to consider

• Container will be in running state as long as the command which was started when container is created is running
• When we dont mention CMD/Entrypoint in Dockerfile based images CMD will be used.
• When we dont expose ports and if base image has Expose by default those will the ports
• While running the container we can statically forward ports by using -p <host-port>:<contianer-port>

docker run -p 80:8080 -d spc:1
docker run -p 8080:8080 -d spc:1

• Docker gives a dynamic way to attach ports to container port by using -P
  
• We can execute commands in running container using docker container exec

Sample Application – Java

• This application is developed in spring boot
• The jar file is available for download from here
• Steps:
  • Install java 17 or above
  • download jar file wget https://referenceappslt.s3.ap-south-1.amazonaws.com/spring-petclinic-3.3.0-SNAPSHOT.jar
  • run the app java -jar spring-petclinic-3.3.0-SNAPSHOT.jar
• Application runs on port 8080
• Lets start containerizeing this application

FROM eclipse-temurin:17
LABEL project="learning" 
LABEL author="khaja"
ADD https://referenceappslt.s3.ap-south-1.amazonaws.com/spring-petclinic-3.3.0-SNAPSHOT.jar /spring-petclinic-3.3.0-SNAPSHOT.jar
EXPOSE 8080
# CMD Executes when the container is started
CMD [ "java", "-jar", "/spring-petclinic-3.3.0-SNAPSHOT.jar" ]

• Refer Here for the changes done
• Lets findout the user using which our application is getting started
  
• Our application is also copied to root directory
• Creating a directory for application Refer Here
• Exercise: Image is created from the following Dockerfile. The contianer is not starting (exited state) Findout the reason

FROM eclipse-temurin:17
LABEL project="learning" 
LABEL author="khaja"
USER nobody
ADD https://referenceappslt.s3.ap-south-1.amazonaws.com/spring-petclinic-3.3.0-SNAPSHOT.jar /apps/spring-petclinic-3.3.0-SNAPSHOT.jar
EXPOSE 8080
# CMD Executes when the container is started
CMD [ "java", "-jar", "/apps/spring-petclinic-3.3.0-SNAPSHOT.jar" ]