2.docker pull nginx: This command helps you pull images from the central docker repository.

3.docker images: This command helps you in listing all the docker images, downloaded on your system.

4.docker run –it -d centos: This command helps in running containers, from their image name.

-It = which basically makes the terminal interactive.

-d = which means run the container as a daemon and that should be run the container in the background.

5.docker ps: This command helps in listing all the containers which are running in the system.

6.docker ps –a: if there are any stopped containers, they can be seen by adding the “-a” flag in this command.

7.docker stop container ID (or) name: This command will stop the containers which are running.

8.docker exec –it container id bash (current terminal space): for logging into/accessing the container, one can use the exec command.

9.docker kill container id: This container kills the container by stopping its execution immediately. The difference between ‘docker kill’ and ‘docker stop’ gives the container time to shutdown in any situations, when it is taking too much time for getting the container to stop, one can opt to kill it.

10.docker rm container Id: To remove a stopped container from the system, we use the rm command.

11.docker rmi image id: To remove an image from the system we use the command “rmi”.

# Comment

INSTRUCTION arguments

A Dockerfile must start with a FROM instruction.

There are multiple INSTRUCTIONS that are available in Dockerfile, some of these include:

• FROM
• RUN
• CMD
• LABEL
• EXPOSE

FROM: The FROM instruction specifies the Base Image from which you are building.

RUN: In this we can run our commands for installing the packages

ADD: This instruction will give the output of converting tar file in to normal file and it will add in to that particular directory.

COPY: This instruction will give the output of copying the content and nothing will do more than that in the docker instruction. This instruction will give you the result of moving files.

COPY and ADD are both Dockerfile instructions that serve similar purposes. They let you copy files from a specific location into a Docker image.

EXPOSE: The EXPOSE instruction informs Docker that the container listens on the specified network ports at runtime.

The EXPOSE instruction does not actually publish the port. It functions as a type of documentation between the person who builds the image and the person who runs the container, about which ports are intended to be published.

HEALTHCHECK: The HEALTHCHECK instruction Docker allows us to tell the platform on how to test that our application is healthy. When Docker starts a container, it monitors the process that the container runs. If the process ends, the container exits.  That’s just a basic check and does not necessarily tell the detail about the application.

We can specify certain options before the CMD operation, these includes:

HEALTHCHECK –interval=5s CMD ping -c 1 172.17.0.2

• –interval=DURATION (default: 30s)
• –timeout=DURATION (default: 30s)
• –start-period=DURATION (default: 0s)
• –retries=N (default: 3)

ENTRYPOINT: The best use for ENTRYPOINT is to set the image’s main command. This doesn’t allow you to override the command. It is important to understand the distinction between CMD and ENTRYPOINT

Sample Code Snippet:

FROM ubuntu

ENTRYPOINT [“top”, “-b”]

CMD [“-c”]

WORKDIR: The WORKDIR instruction sets the working directory for any RUN, CMD, ENTRYPOINT, COPY and ADD instructions that follow it in the Dockerfile.The WORKDIR instruction can be used multiple times in a Dockerfile.

ENV: The ENV instruction sets the environment variable <key> to the value <value>.

You can use -e, –env, and –env-file flags to set simple environment variables in the container you’re running or overwrite variables that are defined in the Dockerfile of the image you’re running.

The docker container exec command runs a new command in a running container. The command started using docker exec only runs while the container’s primary process (PID 1) is running, and it is not restarted if the container is restarted.

docker exec [OPTIONS] CONTAINER COMMAND [ARG…]

Docker attach:

When we start a docker container, we need to decide if we want to run in a default foreground mode or the detached mode.

It will attach local standard input, output, and error streams to a running container.

docker attach [OPTIONS] CONTAINER

This command will stop the containers which are running.

docker stop [container id or name]

Docker Kill:

This command will kill the container by stopping its execution immediately.

docker kill [container id or name]

The difference between ‘docker kill’ and ‘docker stop’ gives the container time to shutdown in any situations, when it is taking too much time for getting the container to stop, one can opt to kill it.

It will suspends all processes in the specified containers. It means that the processes in the container stop running, and they are be able to resumed later.

docker pause [container id or name]

DOCKER UNPAUSE:

It will resumes all the processes in the specified container. It means recovery container all processes.

docker unpause [container id or name]

It is the world’s leading software container technology which is used for creating and managing containers.
Docker is an open platform, once we build a docker container, we can run it anywhere, say it windows, Linux, mac whether on a laptop, data center, or in the cloud.
The whole idea of docker is for developers to easily develop applications, ship them into containers which can then be deployed anywhere.

The Docker components are divided into two categories;

a)Basic b) Advanced

a)Basic components

1) Docker client: Whenever we are using docker commands, the client sends the commands to dockerd, which carries them out. The docker command uses the Docker API. Then the docker can communicate with more than one daemon.

2)Docker image: Docker Image is a file that contains all the necessary dependency and configurations which are required to run an application: code, runtime, system tools, system libraries and settings.

3)Docker Daemon : It will listens the docker API requests and manages docker objects such as images, containers, networks, and volumes. A daemon can also communicate with other daemons to manage Docker services.

4)Docker Networking: Docker takes care of the networking aspects so that containers can communicate with other containers and also with the Docker Host. Docker networking subsystem is pluggable, using drivers. There are several drivers available by default and provides core networking functionality.

• bridge 
• host
• overlay
• macvlan
• none

5)Docker registry: A Docker registry stores Docker images. Docker Hub is a public registry that anyone can use, and Docker is configured to look for images on Docker Hub by default. You can even run your own private registry.

When you use the docker pull or docker run commands, the required images are pulled from your configured registry. When you use the docker push command, your image is pushed to your configured registry.

6)Docker container: These are the live running instances of Docker images. And it is isolated environment where we can run application and its libraries and dependencies.

b)Advanced Concepts:

1)Docker Compose: Sometimes you want to run multiple containers but as a single service. This task can be accomplished with the help of Docker compose as it is specifically designed for this goal. It follows the principle of isolation between the containers but also lets the containers interact with each other. The Docker compose environments are also written using YAML. 

2)Docker swarm: Docker Swarm is a container orchestration tool that is natively supported by Docker. A node is an instance of the Docker engine participating in the swarm. To deploy your application to a swarm, you submit a service definition to a manager node. The manager node dispatches units of work called tasks to worker nodes.