Docker

In the previous post we read about how to pull and run a container with single RUN command. Here we will see how to build a container from scratch, perform operation on that container and push our container to docker hub.

Before we dive deeper, we need to understand that container is only runtime instance of a Image. And same image can be used to create multiple containers.Also, Each container is identified with a unique Container ID.

To list all the running containers

sudo docker ps

To list all the containers dead or alive

sudo docker container ls -all

Commands to perform operations on Continers

Docker container is formed when we create a runtime instance of Image. Here is life cycle of a docker contianer

Here are all the operations which can be performed on docker container (you can get containerID by using the command – sudo docker container ls -al)

Go inside a Container (attach to a container)

sudo docker attach containerID

Top processes within a container

sudo docker top containerID

Stop a running container

sudo docker stop containerID

Delete a Container

sudo docker rm containerID

Check stats of a container (CPU/mem)

sudo docker stats containerID

Pause processes in running contianer

sudo docker pause containerID

Un-Pause processes in running contianer

sudo docker unpause containerID

Kill processes inside a container

sudo docker kill containerID

Building you own Docker Images

There are tonnes of images available on Docker HUB but you can always create your own image and then push it to docker hub.

Docker images are always created with a file called Dockerfile (D capital). You can have docker file in any directory of your system but your docker file will be stored by docker daemon in your local docker registry.

Editing of Docker file Check Here.

For now we will see how to build a Docker Image with Dockerfile. CD to the directory where your Dockerfile is stored and fire the build command (-t used to tag the image with the name dockerImage)

sudo docker build -t dockerImage

This docker Image will now be stored in our local docker registry (can be checked by – sudo docker images)

Pushing Docker Image to Docker Hub

Now that we have created our image in local registry, we will upload it to the Docker HUB so that it is available on the cloud

First create a account on docker hub and then login to docker hub from your local PC

sudo docker login

There is a notation for all the images present on dockerhub – username/imageName:tag

Now we will tag our image (it will take local image and tag it as Dockerhub image locally)

sudo docker tag dockerImage username/imageName:tag

Finally we will push our image to Dockerhub

sudo push username/imageName:tag

Now if somebody wants to run our image in their system, they just have to execute run command and our docker image will be first pulled and then run into the system

sudo docker run -it username/imageName:tag

That’s all for the basics of docker, the next articles on docker will talk about some advance processes we can do with docker.

Docker is a container management service which helps to Build-Ship-Run our software anywhere. In simple terms Docker aggregates all the dependencies and files of our software into a single container, which is then treated as an independent unit and can be shipped and run anywhere. Also, Docker containers are platform and OS independent.

If you ever read about docker, you must be knowing how it is advantageous over using Virtual Machines, but there are many other benefits of using docker :-

1. Docker containers are allocated resources(CPU, Memory, Storage) dynamically based on their usage; unlike VM’s in which we have to pre-allocate all the resources.
2. Reduced startup time as docker runs on top our host OS – saves boot-up time.
3. We can have multiple instances of programs within a single container, or have multiple containers which can communicate with each other.
4. Provides a consistent computing environment throughout the whole SDLC (dev,qa,prod)

Here is an image which explains how Docker is different from VM’s

Both Docker Container and VM requires an Infrastructure(hardware) and Host Operating System. Unlike Docker, Virtual Machines require another software called hypervisor -which helps to run Guest OS on top of Host OS- which require additional hardware resources and most of the functionalities of the guest OS are never used by our apps.

Whereas, Docker Containers – which are package of our app and its dependencies – just require a Docker Daemon which runs over our Host OS and is very light weight. Wait! whats docker daemon, hmm let us first go through all the terms which we will come across while working with Docker

Important terms related to Docker

• Docker Engine (Docker Daemon) : Docker engine is a part of docker which runs Docker container. And Daemon is just a computer program that runs as a background process, rather than being under the direct control of an interactive user. So Docker engine/ Docker Daemon runs in background and we run our containers on top of it.
• Docker Container : A Docker container is a live running instance of a Docker image. A container is a standard unit of software that packages up code and all its dependencies so the application runs quickly and reliably from one computing environment to another.
• Docker Image : A Docker Image is the template (application plus required binaries, libraries, env variables and config files) needed to build a running Docker Container (the running instance of that image).
• Docker HUB : Docker hub is a repository on cloud for all your docker images (like github for code). It host pre-build images of famous software’s like wordpress, Ubuntu, centOS etc. You can also push your images to docker hub which can be used by anyone.

That’s all for this tutorial, in next tutorial we will dive into some technicalities and see how to install docker and how to pull and run a container.