Docker Interview Questions and Answers
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Best Docker Interview Questions and Answers
Coursejet provides top 50 Docker Interview Questions and Answers for aspirants to crack their Docker interview. Here, we have compiled all the important topics of Docker like Docker container, Docker object, Docker architecture, Docker image, repository, hypervisor, virtualization, containerization, Docker registry, Docker file, Kubernetes and more. From beginners to experts, everyone can excel their career using these top 50 Docker interview questions and answers. Apart from this, we have also listed some of the useful command and syntax for aspirants to brush up their Docker skill. This will be a one-stop resource for all aspirants who are looking Docker interview questions.
In these days, Docker is highly used by most of the organizations and so expert Docker specialists are in huge demand and they are paid well too. So, if you are interested in the field of Docker, join Coursejet and get certified. Make use of the Docker interview questions and build confidence before you attend your interview.
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Frequently Asked Docker Interview Questions and Answers
We have prepared these questions in consultation with the top Docker recruiters in the industry. And, all these questions are frequently asked in the Docker interview. Keep preparing genuinely and attain your most preferred career in life. We wish you all success in your life. Prepare confidently, face interview with confidence and succeed in your life.
The term “Containerization” can be explained with an example. We all know that any code designed to work on a particular machine will not work perfectly on any other machine and this issue can be resolved using the concept “Containerization” in which a code generated and deployed are combined will all the dependencies and files associated with it and this combination can be referred to as a container. Now, if you want to run a code in any other machine, then you can deploy this container as it has all the files and dependencies into it such that the machine works without any errors. Some of the examples of containerization can be Kubernetes and Docker.
And, in this blog, you will get the top 50 Docker Interview questions and answers.
This following table indicates the difference between Docker and Kubernetes:
Docker | Kubernetes |
Docker can be set up at ease but without a strong cluster | Kubernetes assures a robust cluster but the setup process is tedious |
Docker is 5x times more scalable than Kubernetes | It ensures scalability but not as Docker |
It does not support GUI | It supports GUI |
Docker consists of a tool named Docker swarm which is a clustering and scheduling tool that can provide automatic load balancing | In Kubernetes, load balancing has to be done manually |
The process that is used to create a software-based virtual version of essentials like servers, computing storage, application and more which are created using a single physical hardware system is known as the virtualization that segregates a system into various other sections which can be distinct individual systems or separate. And, this splitting can be possible with the help of the Hypervisor software. The virtual environment which is created using Hypervisor is known as the Virtual Machine.
Docker | Virtual Machine |
The host OS is shared by all the containers in the Docker | Every virtual machine will be executed only on its particular OS |
It assures a very speedy startup time | It assures slow startup time |
Docker ensures process-level isolation | Virtual Machine or VM ensures full isolation |
Docker furnishes low security | Virtual Machine guarantees a high level of security |
This question is frequently asked in Docker interviews recently, so prepare the answer to this question before you attend a Docker interview. This question can also be asked as the difference between virtual machines and containers, so aspirants have to be clear in answering this question.
An isolated environment to run an application is known as the container and the userspace available is solely provided for the application thus deployed. The changes done on the container will never affect the host or the other containers that are being executed on the same host. But, in virtualization, the completely virtual environment for guest like kernel can be created using hypervisors.
Containers are defined to be an abstraction of the application layer while the abstraction of the virtual machine can be the hardware layer.
Every container can be stated as a unique application while every virtual machine can be stated as a physical machine.
The process of validating the developed and integrated code several times to ensure it works fine before it reaches the end-user is known as continuous testing.
The stopped containers, the networks that are not used, all the dangling images and all the build caches can be removed using the Docker system prune command.
Aspirants can also expect this question from Docker recruiters, so have a glance at the answer and attend this question in your interviews confidently. Listed below are some of the main benefits of using Docker container:
- It maintains consistency among various progressive release cycles.
- It is simple; easy to install and cut downs the operational cost.
- It can expand the lifecycle of any application easily.
- Any software can be transferred 7x times faster by Docker than the other container platforms.
- It does not allow any irrelevant files to enter into the container.
In recent times, this question is often by the Docker interviewers to check the ability of the aspirants. Following are some of the lifecycles present in the Docker container:
- Create a container
- Run the container
- Pause the container (optional)
- Un-pause the container (optional)
- Start the container
- Stop the container
- Restart the container
- Kill the container
- Destroy the container
For more important Docker interview questions, make use of the blog posted by Coursejet. By preparing all these top 50 Docker interview questions and answers, you can surely crack the interview and get placed in the top MNC companies of your desire with an attractive salary package.
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This is one of the important questions asked in most of the Docker interviews, so prepare this question before you attend an interview:
- The command to start a Docker container is docker start container_id
- The command to stop a Docker container is docker stop container_id
- The command used to restart a Docker container is docker restart container_id
Docker is a one-stop resource, and it is usually light-weight as it makes use of only the host that comes under kernel apart from developing its own unique hypervisor.
The software that makes virtualization smooth is known as the “Hypervisor” which can also be stated as “Virtual Machine Monitor”. A Hypervisor usually separates the host system and defines the resources that have to be redirected to the entire separated virtual environment. Also, with Hypervisor, we can access multiple OS in a unique host system.
A build is nothing but combining the source code together and checking whether the code works fine in the form of a single unit. While creating a build process, the source code will be put to various processes like compilation,
Aspirants might also face this question apart from “What is Hypervisor?” in the Docker interviews. So, prepare this question too if you are nearing your interview.
There are two types of Hypervisors and they are as follows:
Type I or Native Hypervisor or Bare Metal Hypervisor: This type is being executed on the underlying host system and has direct access to the hardware of the host system and so it doesn’t require any base server operating system.
Type II or Hosted Hypervisor: This type of Hypervisor utilizes the operating system of the underlying host system.
The key aspects or the core principle of DevOps are listed below:
- Infrastructure as code
- Continuous deployment
- Automation
- Monit
However, both Docker and Hypervisor are similar there are certain differences too. Docker uses only little resources and so it can be stated lightweight and also Docker hosts kernel apart from developing a Hypervisor.
Following are some of the essential features of Docker:
- Simple architecture
- Maximum productivity
- The easy application isolation technique
- Smart security management
- Integration of Docker Swarm which is a clustering and scheduling mechanism for Docker
- Ensures routing mesh
- Guarantees reliable service
The Docker objects are categorized into Docker images, services and containers which are explained as below:
Docker images: It can be denoted as a read-only template that holds the instruction to develop a Docker container.
Services: It can be used in the scaling process of containers over several Docker daemons and these perform together as a Docker swarm.
Containers: It is one of the runnable instances of an image.
Networks and Volumes can also be listed as Docker objects in some cases.
The major question asked in most of the Docker interview; spend a few minutes to go through this question to crack your interview.
The Docker architecture holds a Docker engine, also known as a client-server application that assures three valid elements or components which are explained as below:
It undergoes a daemon process which is nothing but a server that comes under a long-running program concept.
It also consists of a REST API which indicates and instructs the daemon about its process. The Docker REST API which makes use of the CLI (Command Line Interface) to manage the daemon via CLI commands and simple coding.
The work of a Docker can be inclusive and similar to a client-server architecture that requires a client, host which can be daemons that consist of containers and a docker registry to operate effectively with an image.
Docker client: This is the first step using which a Docker user can interact effectively with the Docker. Also, a docker client can easily communicate with several docker daemons.
Images: The template if Docker can be stated as Images which contains an application’s valid elements. Also, Docker images can be referred to as the replicas of Docker containers.
Docker Daemon or Host: The commands are being accepted by Docker Daemon and these commands are provided by the client or REST APIs. Clients usually execute an activity based on the command-line interface. In every system, a Docker Daemon will have a Docker registry.
Docker Registry: A Docker registry is placed in the host system that builds and caters images which are distributed among the members of a particular team. And, this Docker registry can be public or private depending on the administrator’s preference.
Docker registry can be a distributor and a storage system that stores and caters Docker images. All docker registries can be stored in the docker repository. The docker registry can be either public or private based on the administrator’s necessities.
If a Docker registry is private, the docker images will be generated locally and it will be stored in the docker hub and no users of docker hub can access it.
If a Docker registry is public, the docker images stored in the repositories can be directly accessed by all the users of docker hub.
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Docker containers are created by Docker images and these Docker images have to be stored in a registry which is known as the Docker hub from which a user can select images and develop customized containers and images. This Docker hub is referred to be the world’s largest public repository that is available to store the image containers.
The Docker container’s source can be referred to as the Docker image which can also be used to develop containers. Whenever a user executes a Docker image, an instance of the container will be created. And, these Docker images can be deployed to any of the Docker environments.
The following command has to be used in order to push or add a new image into the Docker registry.
docker push myorg/myimg
You can expect this question in your Docker interview for sure. The unique benefits of Docker over the other containerization techniques are as follows:
- A Docker container can be executed on both the enterprise IP system and PC.
- With the help of Docker hub present in the Docker which is known as the repository of the containers, we can download and deploy the necessary applications from the central location.
- Also, the applications thus created can be catered with the containers.
A native clustering for Docker can be defined as the Docker swarm which can be used to transform a Docker pool into a single and virtual Docker host. Docker swarm can also be helpful for Docker API and any other tools that interact with Docker daemon can make use of Docker swarm to scale up to multiple hosts directly.
Yes, it is possible with the help of Docker swarm as it consists of two different nodes namely – Manager node and Worker node.
This is one of the twisted questions in Docker interviews. Directly, a recruiter can ask what a Docker Compose is but at the time, you may expect this question also in your interview, so be prepared in all the ways to answer the question confidently in order to grab success.
Yes, we can execute multiple containers using a single server with the help of Docker compose in which every container will be executed separately but it can interact effectively with the other containers too. And, every Docker compose files will prefer only YAML language.
Yes, for a Docker compose file we can make use of JSON rather than YAML file with the help of the following command:
docker-compose -f docker-compose.json up
This is one of the important questions, so dear aspirants don’t miss going through this question before your Docker interview.
docker swarm init –advertise-addr <manager IP>
Using the command mentioned above, we can easily create a Docker swarm.
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Docker namespace is actually used to create an isolated workspace which can also be defined as the containers. Whenever a container starts to perform, a namespace for that particular container will also be created. Docker namespace can also be stated as a layer of seclusion or a layer of isolation for the containers as every container works in a unique namespace and it can access only those namespace.
For a Docker container, it is advised to go with a stateless application rather than a stateful application.
A Docker file contains all the commands or instructions that are passed to the Docker in order to simplify the process of creating images.
These two instructions of Docker file explains which command should be executed while a container is performing and this process is done under three important conditions which are as follows:
- Any one command from CMD or ENTRYPOINT should be specified by Docker file during this process.
- If the container is executable, then a Docker file should prefer ENTRYPOINT.
- CMD will be overridden if a container runs with an alternative argument.
No data loss will occur when we exit from the Docker container because every data will be written by an application to a disk to preserve those data. And, this process is continuous and will be stopped only when the Docker container is completely deleted.
This is one of the important questions asked in most of the Docker interviews. So, brush up your preparation by going through this question for sure before you enter into a Docker interview.
The basic Docker commands are as follows:
- Docker push: It is used to push an image or a repository into a registry
- Docker run: It can be used to run a new command in the container
- Docker pull: It can be used to pull an image or a repository from a registry
- Docker start: It is used to start one or more containers at a time
- Docker stop: This command actually stops all the containers that are running at that point of time
- Docker search: It can be used to search for an image in the Docker hub
- Docker commit: This command is specially used to commit a new image
This is one of the important questions in Docker interview. And, this question can also be asked as “What are the prerequisites to install Docker in Windows?” so, if your recruiter ask this question, answer as described below.
No, Docker can also be executed in Windows platform. But there are a few prerequisites to install Docker in Windows and they are as follows:
- Check that you have Windows 10 64 bit with 2GB RAM.
- Windows 7, 8, 8.1 can also be preferred with same 2 GB RAM.
- Users have to activate virtualization from some of the trustworthy Docker websites.
- Also, compatible toolbox for Docker has to be downloaded to run smoothly in the older versions of the Windows.
Listed below are some of the storage drivers in Docker:
AUFS: It is one of the firm drivers and if the team of production is ready to start the production operations and in that case, AFUS will the appropriate driver to be preferred because AUFS preserves spaces within the containers by utilizing the available memory perfectly. It is compatible with the service-oriented application and ensures efficient write access.
Overlay Driver: Overlay driver is also similar to AUFS as it makes use of the memory well and preserves more space. It is highly compatible with laboratory testing applications.
Btrfs: It ensures effective write access and is used to control various built pools and performs basic operations of Linux kernel.
ZFS: It is also a firm driver similar to both AUFS and Overlay drivers as it is compatible with both service-oriented applications and laboratory testing applications.
Device Mapper: This is one of the essential storage drivers which assure the best Docker experience to the team of developers. It is also a firm driver that is compatible with service-oriented applications as it is identical to both AUFS and ZFS. And, it also ensures basic operations like the Linux kernel.
The default networks present in Docker are as follows – Bridge, None, Macvlan, Overlay and Host.
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This is the most common question asked in the Docker interviews frequently.
/var/lib/docker/volumes – This is the location where Docker volumes are stored.
The tool that allows you to install Docker engine on a specific virtual host which can be effectively managed using the Docker machine commands is known as the Docker machine.
$ docker version is the command using which you can identify the version of Docker client and Docker server.
Docker is used in the following areas:
- It simplifies code deployment and configuration.
- It helps in maintaining the consistency of the code pipeline.
It ensures rapid deployment and multi-tenancy.
No, a paused container cannot be removed from the Docker. In order to remove, it has to be in the stopped state.
Docker Cloud is one of the extra supports provided by Docker using which a developer cloud can perform several activities like nodes, uninterrupted integration, software deployment, cloud response and uninterrupted deployment.
docker login is the syntax using which users can enter into the cloud repository.
Listed below are some of the Linux administrations in which Docker can be executed at ease:
- Ubuntu 12.04, 13.04 et al
- Fedora 19/20+
- RHEL 6.5+
- CentOS 6+
- Gentoo
- ArchLinux
- openSUSE 12.3+
- CRUX 3.0+
Listed below are some of the services in which Docker is used:
- Amazon EC2
- Amazon ECS
- Google Compute Engine
- Microsoft Azure
- Rackspace
$ docker build <path to docker file>
The syntax listed above is used to build a Docker file.
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