Docker-2

Docker Dairy-2

Why do we need Docker?

The list of benefits is the following:
Faster development process. There is no need to install 3rd parties like PostgreSQL, Redis, Elasticsearch. Those can be run in containers.
Handy application encapsulation (you can deliver your application in one piece).
Same behaviour on local machine / dev / stage / production servers.
Easy and clear monitoring.
Easy to scale (if you’ve done your application right it will be ready to scaling not only in Docker).
Supported platforms

Docker’s native platform is Linux, as it’s based on features provided by Linux kernel. However, you can still run it on macOS and Windows. The only difference is that on macOS and Windows Docker is encapsulated into a tiny virtual machine. At the moment Docker for macOS and Windows has reached a significant level of usability and feels more like a native app.

Moreover, there a lot of supplementary apps such as
Kitematic or Docker Machine which help to install and operate Docker on non Linux platforms.
Terminology
Container — running instance that encapsulates required software. Containers are always created from images.
Container can expose ports and volumes to interact with other containers or/and outer world.
Container can be easily killed / removed and re-created again in a very short time.
Image — basic element for every container. When you create an image every step is cached and can be reused (Copy On Write model). Depending on the image it can take some time to build it. Containers, on the other hand can be started from images right away.
Port — a TCP/UDP port in its original meaning. To keep things simple let’s assume that ports can be exposed to the outer world (accessible from host OS) or connected to other containers — accessible only from those containers and invisible to the outer world.
Volume — can be described as a shared folder. Volumes are initialized when a container is created. Volumes are designed to persist data, independent of the container’s lifecycle.
Registry — the server that stores Docker images. It can be compared to Github — you can pull an image from the registry to deploy it locally, and you can push locally built images to the registry.
Docker hub — a registry with web-interface provided by Docker Inc. It stores a lot of Docker images with different software. Docker hub is a source of the “official” Docker images made by Docker team or made in cooperation with the original software manufacturer (it doesn’t necessary mean that these “original” images are from official software manufacturers). Official images list their potential vulnerabilities.This information is available for any logged in user. There are both free and paid accounts available. You can have one private image per account and an infinite amount of public images for free.

Example 1: hello world

It’s time to run your first container:

docker run ubuntu /bin/echo 'Hello world'

Console output:

Unable to find image 'ubuntu:latest' locally  
latest: Pulling from library/ubuntu  
d54efb8db41d: Pull complete  
f8b845f45a87: Pull complete  
e8db7bf7c39f: Pull complete  
9654c40e9079: Pull complete  
6d9ef359eaaa: Pull complete  
Digest: sha256:dd7808d8792c9841d0b460122f1acf0a2dd1f56404f8d1e56298048885e45535  
Status: Downloaded newer image for ubuntu:latest  
Hello world

docker run is a command to run a container.
ubuntu is the image you run, for example, the Ubuntu operating system image. When you specify an image, Docker looks first for the image on your Docker host. If the image does not exist locally, then the image is pulled from the public image registry — Docker Hub.
/bin/echo ‘Hello world’ is the command that will run inside a new container. This container simply prints Hello world and stops the execution.

Docker-1

Docker Introduction

Docker is the world’s leading software container platform. Developers use Docker to eliminate “works on my machine” problems when collaborating on code with co-workers. Operators use Docker to run and manage apps side-by-side in isolated containers to get better compute density. Enterprises use Docker to build agile software delivery pipelines to ship new features faster, more securely and with confidence for both Linux and Windows Server apps.

Using containers, everything required to make a piece of software run is packaged into isolated containers. Unlike VMs, containers do not bundle a full operating system - only libraries and settings required to make the software work are needed. This makes for efficient, lightweight, self-contained systems and guarantees that software will always run the same, regardless of where it’s deployed.

devlopers using Docker don’t have to install and configure complex databases nor worry about switching between incompatible language toolchain versions. When an app is dockerized, that complexity is pushed into containers that are easily built, shared and run. Onboarding a co-worker to a new codebase no longer means hours spent installing software and explaining setup procedures. Code that ships with Dockerfiles is simpler to work on: Dependencies are pulled as neatly packaged Docker images and anyone with Docker and an editor installed can build and debug the app in minutes

Docker is both a daemon (a process running in the background) and a client command. It’s like a virtual machine but it’s different in important ways. First, there’s less duplication. With each extra VM you run, you duplicate the virtualization of CPU and memory and quickly run out resources when running locally. Docker is great at setting up a local development environment because it easily adds the running process without duplicating the virtualized resource. Second, it’s more modular. Docker makes it easy to run multiple versions or instances of the same program without configuration headaches and port collisions. Try that in a VM!

Because Docker is an open platform, anyone can contribute to its development to build out features that aren’t yet available. Best of all, Docker offers version control (for free!).

With Docker, developers can focus on writing code without worrying about the system on which their code will run. Applications become truly portable. You can repeatably run your application on any other machine running Docker with confidence. For operations staff, Docker is lightweight, easily allowing the running and management of applications with different requirements side by side in isolated containers. This flexibility can increase resource use per server and may reduce the number of systems needed because of its lower overhead, which in turn reduces cost.”

If you face any problem while practicing feel free to comment it and Bookmark this blog for quick reference.We will try to help you

ThanksDevops Desk Team