What is Docker - Important to know about Docker for SDET

                             

Docker is a set of platform as a service (PaaS) products that use OS-level virtualization to deliver software in packages called containers. 

Containers are isolated from one another and bundle their own software, libraries and configuration files; they can communicate with each other through well-defined channels. Because all of the containers share the services of a single operating system kernel, they use fewer resources than virtual machines.

What is Docker?

Docker creates simple tooling and a universal packaging approach that bundles up all application dependencies inside a container which is then run on Docker Engine.

Docker Engine enables containerized applications to run anywhere consistently on any infrastructure, solving “dependency hell” for developers and operations teams, and eliminating the “it works on my laptop!” problem.

Docker is a set of platform as a service products that use OS-level virtualization to deliver software in packages called containers.

Package Software into Standardized Units for Development, Shipment and Deployment


What is Container?
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. A Docker container image is a lightweight, standalone, executable package of software that includes everything needed to run an application: code, runtime, system tools, system libraries and settings.

Container images become containers at runtime and in the case of Docker containers - images become containers when they run on Docker Engine. Available for both Linux and Windows-based applications, containerized software will always run the same, regardless of the infrastructure. Containers isolate software from its environment and ensure that it works uniformly despite differences for instance between development and staging.

Docker containers that run on Docker Engine:
Standard: Docker created the industry standard for containers, so they could be portable anywhere
Lightweight: Containers share the machine’s OS system kernel and therefore do not require an OS per application, driving higher server efficiencies and reducing server and licensing costs
Secure: Applications are safer in containers and Docker provides the strongest default isolation capabilities in the industry

Comparing Containers and Virtual Machines

Containers and virtual machines have similar resource isolation and allocation benefits, but function differently because containers virtualize the operating system instead of hardware. Containers are more portable and efficient.

CONTAINERS:
Containers are an abstraction at the app layer that packages code and dependencies together. Multiple containers can run on the same machine and share the OS kernel with other containers, each running as isolated processes in user space. Containers take up less space than VMs (container images are typically tens of MBs in size), can handle more applications and require fewer VMs and Operating systems.

VIRTUAL MACHINES:
Virtual machines (VMs) are an abstraction of physical hardware turning one server into many servers. The hypervisor allows multiple VMs to run on a single machine. Each VM includes a full copy of an operating system, the application, necessary binaries and libraries - taking up tens of GBs. VMs can also be slow to boot.

Most useful Docker commands for Automation tester

Create Jenkins job using groovy script (Jenkins file)

Create Jenkins job using groovy script (Jenkins file)

Inside your project create a new file with name Jenkinsfile with below content:

pipeline {

    agent any

    stages {

        stage ('Compile Stage') {

            steps {

                withMaven(maven : 'apache-maven-3.6.3') {

                    bat 'mvn clean compile'

                }

            }

        }

        stage ('Testing Stage') {

            steps {

                withMaven(maven : 'apache-maven-3.6.3') {

                    bat 'mvn test'

                }

            }

        }

        stage ('Install Stage') {

            steps {

                withMaven(maven : 'apache-maven-3.6.3') {

                    bat 'mvn install'

                }

            }

        }

    }

}

Push the code changes in Git.

Make sure maven name given in Jenkins Global Configuration should match with the Maven name in Jenkinsfile.

So, as you see in below screenshot, We have used the same maven name in Jenkins file also.

Now create a new Jenkins Pipeline Job, ensure that you have "Pipeline" plugin and "Pipeline Maven Integration" plugin is installed.

Job will look as below, Save the job and build, this will search for the Jenkinsfile and will perform all the stages which we have defined inside.

Once the execution is over, it will show all stages and so it becomes so easy for us for debugging in- case of any failures. This is all about pipeline.

Click on save.

And execute the job.