Docker Interview Questions and Answers

Hypervisor refers to software which has a tendency to make virtualizations possible and it is also known as virtual machine monitor. The hypervisor also segments the host system by allocating the resources to the individual virtual environment. With this utility, the user can have various operating systems on a single host system.

Type of hypervisors are-

• Type 1: It is known as a native hypervisor or bare-metal hypervisor which runs directly under the host system.
• Type 2: It utilizes the underlying host operating system it is also known as a hosted hypervisor.

Note: As we are going through Docker interview questions and answers it is very important to have a brief over what is Docker.

Docker presents a containerization platform packaging applications along with its dependencies together in a container form. It is yours that the applications work seamlessly under any environment (no matter if it is a test, development of production). The Docker containers wrap the piece of software in an entire file system containing the essentials like code, runtime, system libraries, system tools and many more. It also wraps everything which is installed on a server guaranteeing its run time regardless of the environment.

The application and its dependencies are included in Docker containers. It can also share the kernel with various other containers running on individual processes in user space on any of the host operating systems. These containers are not bound to any defined specific infrastructure or any computer or infrastructure. They are compatible with the cloud and runtime instances of images.

A docker image is the fundamental source of Docker container it is better to say that they are used to create the Docker containers. When the user runs these images corresponding instance for the container is developed automatically in it. These images can be used for any other Docker environment as well.

Virtualization is a process of creating the virtual session of computer storage, service or applications which are software-based. This virtual environment is created from a single segment of the physical hardware system and through it, you can split one system into various other sections acting like a separate and distinguishable system. With the help of hypervisor, this splitting is executable and the virtual session created by this medium is known as a virtual machine.

The Docker architecture majorly consists of an engine which refers to a client-server application having three major components, these components are-

• A server which represents the long-running program type known as a daemon process (Docker command)
• A REST API which defines the interface used in the program to talk to the daemon and then follow the instructions
• A command-line interface client
• CLI utilizes the Docker REST API to organize or control Damon with scripting or direct commands.

It is justified in Docker that the containers are made up of Docker images. These Docker images are defined in a separate registry which is known as Docker Hub. From this defined registry it is easy for the users to pick images and use them to create containers and customized images. At present Docker Hub is the world's largest public repository for image containers.

By using and implementing Docker large number of functioning and applications are hosted which are-

• It enables the specification and isolation of applications.
• It promotes rapid deployment in the form of virtualization at the various operating system level.
• Simplify configurations.
• It provides ease with infrastructure level configuration.
• It actively manages the code pipeline offering consistent environment and stability.
• It lowers the utilization of various services in the form of containers.
• It improvises the productivity of developers by providing them concentrated logic.

The lifecycle of a Docker is as follows-

• Create a container
• Run the Docker container
• Pause container
• Unpause container
• Start container
• Stop container
• Restart container
• Kill container
• Destroy container

Docker objects: The Docker objects refer to the Docker images, containers and services. A Docker image is a read-only template having the configuration and runtime instructions for Docker instructions. Under the service instruction scaling of the containers across multiple Docker, daemons are allowed. All this together works as Swarm.

Docker namespaces: It refers to a technology that provides individual and isolated workspaces known as containers. Docker namespaces also provide a layer of isolation for containers.

The most important commands in Docker are-

• Docker- It is used to launch the Docker daemon
• Build- It is used to build image files in Docker
• Create- It is used to create a new container
• Kill- It is used to kill the container
• Commit- It is used to create a new image from the container modifications.

On broad terms, Docker and hypervisor form the same working but still, there is a wide range of differences between them. Docker is a lightweight technology as it raises fewer resources and also hosts kernel. Hypervisor technology creates the Colonel rather than hosting.

Most significant features of Docker from other competitive technologies are-

• The Docker container can be run on PC as well as the company's or Enterprise's IT system.
• As Docker is a repository of containers it can be deployed and downloaded on all the applications from a centralized location
• The applications can be shared actively with all the containers that were created earlier.

Docker Swarm is a way of orchestrating the Docker containers where Dockers can be implemented in a cluster. To support the easy monitoring and Management Docker pools can be converted into an individual Docker Swarm.

Note: This is one of the essential Docker interview questions and answers.

A complete set of instructions that are used to pass on the Docker to help in the image build-up is known as Dockerfile. It can be also considered as a text document having all the necessary commands which are required for creating a Docker image. An automated build can also be created which executes various command lines one after the other.

The difference between Docker and the virtual machine is as follows-

The Docker container can be created from any specific Docker image of the user's preference and the same can be obtained using the command-

Docker run t - i command name

This command will help you create the container and the same will start for you. To check the stability of the Docker container and if it is created or not, you can use the command mentioned below. This command will also check if it is running or not and it will list out all the containers along with their status on the host system where the Docker container is running. Docker ps-a

At present doctor is actively available on the platforms mentioned below-

• Ubuntu 12.04, 13.04
• Fedora 19/20+
• CentOS 6+
• RHEL 6.5
• Gentoo
• ArchLinux
• OpenSUSE 12.3+
• CRUX 3.0

At present Docker is also available on the cloud environment and the platform it supports are-

• Amazon EC 2
• Google compute engine
• Microsoft azure
• Rackspace

The user required Docker-compose up UP is used to start or restart the services which are defined under Docker-compose.yml. In the default attached mode, all the logs from containers will be visible to you. In detached mode composed exits by starting the container but containers pursue running in the background.

The Docker-compose run command is utilized for ad hoc or one-off tasks. They also require the services name in which the user wants to utilize run and only start the container for the same services which are dependent on the running services. It is also used to test or perform administrative tasks like removing or adding data to the volume container.

The Docker-compose start command is used to restart the containers that were created earlier but stopped. With this command, new containers cannot be created.

Docker uses cache to enhance the speed of building the project and other instances. All the commands mentioned in the Docker file are used to build other Docker containers and its outcomes are separately stored in a layer. These layers are built on top of every other layer.

Docker runs the Docker file and makes an effort to execute steps one after the other before the finalization. Developing the Docker images with a Docker file is extremely faster as compared to the provision with ansible. This is possible because of the utilization of Docker cache and supreme based images.

Docker containers are rapidly gaining popularity at the enterprise level and it is certainly becoming an essential part of several professional pipelines. Docker is one of the supreme and effective platforms for organizations that understand the consequences of containerization.

In Docker, there can be as many containers defined per host because Docker does not restrict anyone of them. The only thing to be considered is that every container requires the storage space, memory and CPU supporting the hardware as well. It is also advised to consider the size of application as containers are lightweight and extremely dependent upon the host operating system

No, it is not possible to remove a paused container. Before it can be removed the container needs to be in the stopped state.

This guide of best Docker questions and answers was presented to you by considering all the essentials regarding the same. This will help to increase the crackdown rate of a candidate.