Changing the default process of the container & Working with registry  & Introduction to container Orchestration

Changing the default process of the container

  1. Remove all Docker containers and images. … 
  1. Stop the Docker service. … 
  1. Remove the Docker storage directory. … 
  1. Create a new /var/lib/docker storage directory. … 
  1. Use bind mount to set the new location. … 
  1. Start the Docker service. 

Ex:  Create a dockerfile, for using ubuntu as base image, and install java in it. 

Download jenkins.war  and make execution of “java -jar jenkins.war” as the default process. 

Every docker image come with default process. 

As long as default process is running, the container will be running condition. 

The moment, the default process is closed, the container will be exited. 

Lets remove all the container 

# docker rm -f $(docker ps -aq) 

Observation 1: 

When we start ubuntu container, we use below command 

# docker run –name  c1  -it  ubuntu 


To comeout of the container we use  Ctrl + p + q 

# docker container ls 

( our container c1  is running in the background ) 

Observation 2: 

When we start jenkins container, we use below command 

# docker run –name j1  -d  -P    jenkins/jenkins 

Now, I want to open interactive terminal to enter jenkins 

# docker  exec -it  j1  bash 

( In ubuntu container, I can directly go into -it terminal, 

where as in jenkins i am running an additional command  exec ? ) 

Lets try to go to interactive  terminal  in docker run command ) 

# docker run  –name  j2  -it  jenkins/jenkins 

( we are not getting interactive terminal ) 

I want to run tomcat as container 

# docker run  –name   t1  -d   -P   tomee 

 Lets find the reason 


docker container ls  ( to see the list of containers ) 

Observer the command section. 

It tells you the default process that gets executed, when we start the container. 

Container Default process  


jenkins /bin/tini 

ubuntu /bin/bash 

bash — is nothing but the terminal. 

For linux based container, the default process is shell process  

( ex of shell process are  bash shell, bourne shell etc ) 

Hence we are able to enter -it mode  in ubuntu ) 

We are trying to change the default process of the container. 


# vim dockerfile 

FROM ubuntu 

MAINTAINER logiclabs 

RUN apt-get update 

RUN apt-get install -y default-jdk 

ADD  / 

ENTRYPOINT [“java”,”-jar”,”jenkins.war”] 


Build an image from the dockerfile 

# docker build -t  myubuntu  . 

TO see the list of images  ( we can see our new image ) 

# docker image ls 

TO start container from new image 

# docker run  myubuntu     ( Observe the logs generated on the  

screen, we got logs related to jenkins , jenkins is fully up and running ) 

Its an ubuntu container, it is behaving as a jenkins container ) 

Ctrl +c 

RUn the below command 

# docker ps -a 

For myubuntu   the command is  java -jar  jenkins.war 

For  ubuntu    the commans is     /bin/bash 



Working on docker registry 

Registry is a location where docker images are saved. 

Types of registry 

1) public registry 

2) private registry 

public registry is 

Images uploaded here are available for everyone. 

Usecase: Create a customized ubuntu image, by installing  tree in it. 

Save this container as an image, and upload this image in docker hub. 

Step 1: Create a new account in 

Step 2: Creating our own container 

# docker run –name  c5 -it  ubuntu 

Lets install tree package in this container 

/# apt-get update 

/#  apt-get  install tree 

/# exit 

Step 3: Save the above container as an image 

# docker commit  c5  sunildevops77/ubuntu_img26 

( sunildevops77/ubuntu_img15  — is the image name ) 

Note: Image name should start with docker_id/ 

To see the list of images 

# docker image ls  ( we can see the new image ) 

TO upload the image to  ( docker login command is used ) 


# docker login   ( provide docker_id and password ) 

To upload the image 

# docker push  <image_name> 

# docker push sunildevops77/ubuntu_img26 

login to docker hub to see your image 


Container orchestration 


This is the process of running docker containers in a distributed environment, on multiple docker host machines. 

All these containers can have a single service running on them and they share the resources between each other, even running on different host machines. 

Docker swarm is the tool used for performing container orchestration 



1) Load balancing 

2) scaling of containers 

3) performing rolling updates 

4) handling failover scenarios 


Machine on which docker swarm is installed is called as manager. 

Other machines are called as workers. 

Lets create 3 machines 

Name is as Manager, Worker1, Worker2 

All the above machines should have docker installed in it. 

Install docker using 

( Optional step to change the  prompt ) 

After installing docker in the 1st machine ( Manager ),  Lets change the host name. 

Host name will be available in the file hostname. We will change the hostname to manager. 

# vim /etc/hostname 



After changing the hostname, lets restart the machine 

# init 6 


Similary repeat the same in worker1 and worker2 


 Connect to Manager, install docker swarm in it. 

$ sudo su – 

Command to install docker swarm  in manager machine 

# docker swarm init –advertise-addr  private_ip_of_manager 

# docker swarm init –advertise-addr 

Please read the log messages 

Now, we need to add workers to manager 

Copy the  docker swarm join command in the log and run in the worker1  and worker2 

Open another gitbash terminal, connect to worker1 

sudo su – 

# docker swarm join –token SWMTKN-1-27lf3n7xxqy2u3gb61mvfybk51uqjq9hj4m5uwdd4lcgtgafth-0hmrtwzrcyqv4h7cl3euekq68 

Repeat for worker2  


TO see the no of nodes from the manager 

Manager # docker  node ls   ( we can see manager, worker1  and worker 2)

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