Docker services are extensively
used in IT operations, so it is very important that you start learning from
docker basics. In this article, we will cover the installation and setup of the
docker, along with its specific uses.
Learn web application in
Table of Contents
·
Introduction
to docker
·
Docker
and its terminology
·
Advantages
of docker
·
Installation
and usage
Introduction
to Docker
Docker is a third-party tool developed to
create an isolated environment to execute any application. These applications
are run using containers. These containers are unique because they bring
together all the dependencies of an application into a single package and
deploy it.
Now, to work with docker you will need to
install docker engine in your host. It is a foundation to the docker system,
which basically runs as client-server application. Its daemon process is
referred to as server and the command line interface is referred to as client
and REST API is used to create communication link between client and server.
In Linux, docker client interacts with docker
server through the CLI. Here, terminal is docker client and docker host will
run the docker daemon.
Whereas in windows, to work with docker, we need
to install docker toolbox component in docker host in order to set up
environment on your Windows or iOS.
Docker
and its terminology
When working with docker, one should be
familiar with the following terms :
·
Docker Hub:
It is a repository which available to all who uses docker through cloud.
Through docker hub, one can create, store, test, pull and share container
images.
·
Docker Images : Docker image acts as a template in order to create container. Build
command is used to create docker images. Docker images makes it easy.
·
Docker containers : Containers are said to be isolated environment provided to the docker
image and its dependencies so that it can run independently. The focus of
deploying a container is to update or repair an application or just simply
modify it and share it. When working on an image, container lets you create a
layer of a single command used which make it easy to modify it, or upgrade or
degrade is version.
·
Docker Registry : All the docker images are stored in docker registry. User can either
can have local registry on their system or they can have a public one like
docker hub.
Advantages of docker
·
Easy
to use
·
Faster
scaling systems
·
Better
software delivery
·
Flexibility
·
Provides
isolated environment
·
Supports
software defined networking
·
Rapid
deployment
·
Security
Installation and usage
To install docker,
simply open the terminal of Linux and type the following command :
apt install
docker.io
To check the version
one can use the following command :
docker –version
Further you can run
help command in docker, which is as following, to know all the options that
dokcer provides at your service.
docker --help
Once the docker is up
and running, you can run or pull any image in your docker container. For
instance, here we have run hello-world. When you run the following command, it
will first check your local repository; if the image is not available there
then it will pull it from docker hub.
docker run
hello-world
As we have explained
before, CLI works as a client, so directly from the terminal you can search for
any image you like. Like, here we have searched for ubuntu. One thing to
remember here is that image with more stars will be the most authentic one.
docker search
ubuntu
Once you find your
image, you can pull it into your container with the following command :
docker pull ubuntu
Now to check how many
images you have in your docker, simply type the following command :
docker images
To remove any image,
use the following command :
docker rmi
hello-world
Here, rmi refers to
remove image.
Now, in the details
given by ps command, you can see that the name of our ubuntu image is adoring
curie, which is a random name generated by docker for every image. To, rename
this name we can use following command :
docker run -it -d
–name “ignite” ubuntu
And you can confirm
with the ps command again that the name has been changed as shown in the image
below :
The docker attach command permits you to attach to a running
container using the container ID or name, you can use one instance of shell
only though attach command. But if you crave to open new terminal with new
instance of container's shell, we just need run docker exec.
docker attach ignite
docker exec -i -ignite /bin/bash
Using the ps command
we can see all the processes that are running in docker. There, for this, type
:
docker ps
docker ps -a
To stop the running container, you can use stop command as
shown in the below image, we have stopped the container and its process which
can be confirm with the help of process command. As result there should be no
running process for ignite.
docker stop
If you can export the docker filesystem as a tar archive,
use export command to compress the filesystem of a docker container into tar.
The export commands fetch the whole container like a snapshot of a regular VM.
docker export | gzip > {path for
tar} filename.tar
docker export | gzip > {path
for tar} filename.tar
It will give you a flat .tar archive containing the
filesystem of your container.
When you will export container as tar file, the file has
hash value which can read as:
cat {path of exported tar file} |docker import –
newignitelab
In order to save the image of container which you can upload
on other docker use save command. You
can subsequently load this "saved" images into a new docker instance
and create containers from these images.
docker save | gzip > {path
for tar} filename.tar
docker load -i /home/raj/docker/igniteimage.tar
In order to clear all image and or stop all process of the container.
It will pack the layers and metadata of all the chain required to build the
image.
docker rm -f $(docker ps -aq)
To learn how to setup vulnerable web application setup
using docker from here.
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