Docker basic Tasks: Step by Step Procedure

Task 1: Search & Pull images from Dockerhub

• docker can search and pull images from dockerhub
  • docker search hello-world # search for hello-world image
  • docker search jenkins # search for jenkins image in dockerhub
  • docker search httpd # search for apache httpd image
  • docker search tomcat # search for tomcat image
  • docker pull jenkins/jenkins # pull jenkins:lts image from dockerhub
  • docker pull httpd # pull httpd image
  • docker pull tomcat # pull tomcat image
• by default docker pulls the image with :latest tag. This is not a good practice. Instead pull a specific version of docker image
• go to https://hub.docker.com/r/jenkins/jenkins/tags?page=1&ordering=last_updated and pull the image with tag 2.263.3-lts-slim docker pull jenkins/jenkins:2.263.3-lts-slim

Tsk 2: list all images available on the local server

• docker image ls -a # list all the images on local server

Task 3: delete images

• docker image ls -a # to list images
• docker rmi httpd # remove httpd image from local server

Task 4: launch containers with port and volumes

• containers can be launched with available images or images that are not currently available on local system. Incase , the image is not available locally docker will try to pull it from repository
• launch apache httpd container with 80 port from container mapped to 8888 port on host
• also , the htdocs directory where deployment files should be copied is mapped to /root/my-httpd-files directory on host.
  • docker run -d -p 8888:80 -v /root/my-httpd-files:/usr/local/apache2/htdocs –name ncd-apache1 httpd
  • netstat -nap|grep 8888 # check for port 8888 on host. Remember https is running on 80 inside container
• launch tomcat container with 8080 port from container mapped to 7777 port onn host
• webapps directory of tomcat is mapped to /root/my-tomcat-webapps on host
  • docker run -d -p 7777:8080 -v /root/my-tomcat-webapps:/usr/local/tomcat/webapps –name ncd-tomcat1 tomcat
  • netstat -nap|grep 7777 # check for port 7777 on host. Remember its running on 8080 inside container
  • docker logs ncd-tomcat1 –follow # check the logs of container ncd-tomcat1 . Follow the logs. Press ctrl+c to exit
  • docker inspect ncd-tomcat1 # inspect the meta data of containers. eg: ports , volumes etc
  • deploy a sample application to both apps by copying the file to host mapped directory
  • cp /tmp/apache.html /root/my-httpd-files # copy apache.html for apache server
  • cp /tmp/ncodeit.war /root/my-tomcat-webapps # copy ncodeit.war file for tomcat server
  • docker logs ncd-tomcat1 –follow # check if ncodeit.war file is deployed
  • once launched , apache and tomcat servers can be accessed on host’s exposed ports
  • curl -I :8888/apache.html # httpd server is accessible on 8888 port of host server
  • curl -I :7777/ncodeit/ncodeit.html # tomcat server is accessible on 7777 port of host server
  • you can use any port available on host to map to any port inside the container

Task 5: login to containers & execute commands inside containers

• docker exec -it ncd-tomcat1 /bin/bash # start a bash shell inside a container
• docker exec -it ncd-tomcat1 hostname # run hostname command inside a container
• docker exec -it ncd-tomcat1 top # run top command inside a contaienr. press q to exit

Task 6: stop/start/restart/kill containers

• docker stop ncd-tomcat1 # stop a running container
• docker ps -a # check status of all containers
• docker start ncd-tomcat1 # start a container
• docker ps -a # check status of all containers
• docker restart ncd-tomcat1 # restart a container
• docker ps -a # check status of all containers
• docker kill ncd-tomcat1 # kill the container if its not responding to stop command
• docker ps -a # check status of all containers

Task 7: commit & save existing containers

• sometimes we want to save an existing container as image. To take the image to another system
• _this is not recommended practice. images should not be created from containers. Instead use Dockerfile to create images
  • docker pull ubuntu # pull ubuntu image. Yes, ubuntu also can be run inside a container
  • docker run -it ubuntu /bin/bash # login to ubuntu image
  • apt-get update -y && apt-get install htop -y # inside the container. install htop
  • htop # run htop command inside the container . press q to exit out of htop
  • exit
  • docker ps -a # check all the containers on the host
  • docker commit ncd-ubuntu-image #this container will be in Exited state
  • docker image ls -a # check the images. newly created image should be available now
  • docker run -it ncd-ubuntu-image /bin/bash # launch a new container from image
  • htop # this command is availble without any installation
  • exit
• same thing can be done for any container

Task 8: delete containers

• remove all containers that have “exited” or “created” –
• “created” is a state of the container when a wrong command is executed inside
  • docker ps -a # check status of all containers
  • docker rm
  • docker rm $(docker ps -a -f status=exited -f status=created -q) # remove all containers in exited or created state

Task 9: create dockerhub account

• go to www.docker.com and create a free account for yourself
• login to the account -> click “Create Repository” -> create a new repository
• you will push some images into this repository of your account in the next steps

Task 10: tag images & push images to dockerhub

• tagging in simple words is to give a version to an existing image
• syntax docker tag <existing-image-with-tag> <dockerhub-user>/<remote-image-name-with-tag>
• repository name on dockerhub.com should be same as the image name thats being tagged
• once the tagging is done, login to docker registry with docker login
• then push the image to docker registry using docker push
• lets tag our image and push to the newly created dockerhub account
  • docker pull tomcat:8.5 # pull tomcat 8.5 image from dockerhub official apache repo
  • docker image list -a # list all the images available locally
  • docker tag tomcat:8.5 /tomcat:8.5.ncd # tag can be anything. ncodeitdocker is the username on dockerhub.com
  • docker image ls -a # you will see the newly created image also
• now login to dockerhub.com and create a repository with name “tomcat” . Other repo names will not work
• name of the image and name of repo should be same
  • docker login # provide your dockerhub username/password
  • docker push /tomcat:8.5.ncd # pushes image to repo in your account
• login to dockerhub and make sure the new image is avaialble there
  • docker logout #logout of dockerhub account
  • rm /root/.docker/config.json # remove the stored credentials