DevOps Classroomnotes 12/Apr/2023

Dockerfile Instructions Contd…

• LABEL: This instruction adds metadata Refer Here
  • Refer Here for the changes done for spc image
  • Lets inspect the image docker image inspect spc:1.0.0.1 and observe the labels section
    

ADD, COPY instructions

• ADD instruction can add the files into docker image from local file system as well as from http(s)
• ADD instruction can have sources
  • local file system
  • git repo
  • url
• COPY supports only local file system
• Lets use ADD to download springpetclinic into docker image from url ADD https://referenceapplicationskhaja.s3.us-west-2.amazonaws.com/spring-petclinic-2.4.2.jar /spring-petclinic-2.4.2.jar
  
• Refer Here for the changes
• copy the springpetclinic jar file into some local path on docker host. Refer Here for the changes done

What do we mean by running container in detached mode?

• Lets try to start the docker container jenkins jenkins/jenkins
  
  
• docker container’s STDOUT and STDERR will be attached to your terminal and if we execute ctrl+c the container exits.
• Running container normally will take us to attached mode.
• In detached mode container executes and gives us back the access to terminal
  
• Once we start the container in detached mode we can still view the STDOUT and STDERR by executing docker container attach <container-name-or-id>
• To exit from attach mode Ctrl+PQ

Docker container will be in running state as long as command in cmd is running

• Consider the following Dockerfile

FROM amazoncorretto:11
LABEL author="shaikkhajaibrahim"
LABEL organization="qt"
LABEL project="learning"
# Copy from local file on Docker host into docker image
COPY spring-petclinic-2.4.2.jar  /spring-petclinic-2.4.2.jar
EXPOSE 8080
CMD ["sleep", "10s"]

• We have sleep 10s i.e. this will run for 10s and finish.
• Docker container will move to exited stated once the command in CMD has finished executing
  

Exercise:

• Create a ubuntu vm
• install apache2 and note the ExecStart command for apache2
• install tomcat9 and note the ExecStart command for tomcat9
• stop the services (systemcl stop servicename)
• become a root user (sudo -i)
• try executing the ExecStart command directly and see if the application is running