Docker Interview Questions and Answers
Docker Interview Questions and Answers for beginners and experts. List of frequently asked Docker Questions with answers by Besant Technologies. We hope these Docker interview questions and answers are useful and will help you to get the best job in the networking industry. These Docker interview questions and answers are prepared by Docker Professionals based on MNC Company’s expectations. Stay tuned we will update New Docker Interview questions with Answers Frequently.
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Best Docker Interview Questions and Answers
Here is the list of most frequently asked Docker Interview Questions and Answers in technical interviews. These Docker questions and answers are suitable for both freshers and experienced professionals at any level. The Docker questions are for intermediate to somewhat advanced Docker professionals, but even if you are just a beginner or fresher you should be able to understand the Docker answers and explanations here we give.
In this post, you will get the most important and top Docker Interview Questions and Answers, which will be very helpful and useful to those who are preparing for jobs.
Docker can be defined as an open-source technology that actually runs on the platform called containerization through which one can establish applications through automating them through containers. Docker containerization is a software with an entire set of things to run the code and it also contains the necessary libraries, tools, etc.,
Containerization can be defined as a package of containers with all needed file system inclusive of tools, libraries etc., to run a script in a open source software environment. Through this technology, one can create scripts in an error-free environment. In previous methodologies, scripts written in one system generates errors while running them in other system. This containerization method eradicate that problem. Some of the environments that use containerization are Kubernetes, Docker etc.,
Virtualization can be defined as building an application, server, memory unit etc., as an implied genre. Through virtualization, one can separate a method to several parts of which every single system could function like an unique system. Segregation of methods is possible through software called Hypervisor.
Virtualization can be established by Hypervisor software only. It segregates a system into several sections and assigns to operate every single section to function as a distinct system. Hypervisor will run from the existing system of a host and won’t require a separate OS from a server.
Docker contains three major components: Client, Host and Registry. Client initiates a program which passes a run command and a build command to the host system. The docker containers and docker images were built and stored in host. These were passed to the Registry to execute everything.
For accurate functioning, Hypervisor requires specific hardware whereas a Docker runs on OS. So, Hypervisor performs its operations slowly but Docker performs its operations very fast.
- Open source, user friendly environment
- Developer can run script developed in one system in other/ scripts developed in one version can be run in another.
- Offers well organized basic setup for a user
- User can operate the environment effectively and efficiently.
Docker runs on several platforms of Linux such as Ubuntu 12.04 (and higher), Fedora 19 (and higher),RHEL 6.5 (and higher),CentOS 6 (and higher)etc., Docker functions correctly in Ubuntu Linux kernel version 3.8 or higher than that. “sudo docker version” is the command to check the version of Linux installed and to update the linux version, we can use the command “sudo apt-get update”. This command will download the updates from the internet. Then using the command “sudo apt-get install”, we can install the necessary packages.
Q9) Does Docker runs only on Linux? State the basic system requirements to configure Docker in that platform.
Docker also runs in Windows platform. To install Docker in Windows platform, the user needs Windows 10 64bit with 2GB RAM space. Docker also runs on older versions of Windows namely Windows 7, 8 and 8.1 with 2GB recommended RAM space, but the user has to enable Virtualization through downloading the tool box from the docker website. Docker for windows can be downloaded from www.docs.docker.com/docker-for-windows/. The tool box to run older version of windows can be downloaded from www.docker.com/products/docker-toolbox/.
sudo apt-get install –y docker-engine is the command to install Docker Engine in Linux.
docker run – command that runs a Docker container. docker run image – This command calls the image name to run the docker container
Syntax: docker images sudo docker images – will return the output in the terminator window
Syntax: docker rmi ImageID
The output returned will be sudo docker rmi 8d45hh68hbg67a23. Here, 8d45hh68hbg67a23 represents the image ID of the newcentos image installed.
- There is no option to reschedule dormant nodes automatically.
- Supervising and monitoring is below par. ? There is no provision for storage.
- It is very difficult to make horizontal scaling automatically.
The architecture of docker will contain a Docket engine runs primarily on a server-client software with following important parts. They are:
- The command for docker, which is actually the server with a long run named as daemon process.
- To communicate and command the daemon, REST API is used as an interface.
- Another docker command, CLI (Command line interface)
- To direct and communicate with the daemon process through coding, CLI and REST API were used.
The daemon process is the docker engine, which is the server. With identical or distant host, both the docker engine and its clients have to be run using the commands CLI and REST API.
Through build command, user could be able to create a docker image. Without a docker image, docker containers cannot be built. A separate registry is created to store all these docker images.
After creating docker containers through docker images, there is a separate registry named as docker registry created to store all these docker images. This docker registry is called as Docker hub. Any user can access docker hub to retrieve images for their applications.
Docker containers contain the package for an application and its constraints co-operatively in containers which enables the user to run an application in any environment with version compatibility. Docker containers do not need any infrastructure whereas it can be run on any predefined infrastructure. It also runs on any cloud regardless of its type.
- Docker Containers Virtual Machines
- Requires very less resources Requires many resources
- Performs operations using OS Performs operations using hardware
- Resources of OS can be distributed inside Docker
- Requires separate OS for every single virtual machine
- Initial setup is very easy and flexible to the user
- Virtual machines also provides custom features to the user
- A Docker can be built too fast VMs creation requires more time
- Can be booted in seconds Can be booted in minutes
sudo docker run –it centos /bin/bash
docker top ContainerID sudo docker top 8a45cd6789s (returned value)
docker stop ContainerID
docker rm ContainerID
Docker file contains all the commands a programmer need to call upon in the CLI (Command Line) to organize an image. It is actually a text document which contains all these commands. The instructions present in the text document were automatically read to build images. Docker allows any number of instructions can be executed one after the other.
To segregate Docker containers, Docker name space is used. Docker name space is a feature present in Linux. These name spaces are flexible and can be applied on any hosts seamlessly. Some of the Docker supported name spaces are: Process ID(PID), The net(Networking), Interprocess Communication(IPC),The mount(MNT), Unix time-sharing system(UTS).
Docker sparm helps to build the IT developers to create and control clusters of nodes for Docker to function as a separate and distinct system. Docker swarm is actually a tool used in Docker containers to create and administer clusters.
The life cycle of a Docker container starts from creating a container to destroying it. Its cycle ends after destroying it. The life cycle of a Docker container can be described as follows: Build …….> Compile…….> Pause/Resume(if needed)…….> Start………> Stop…….> Reset ……> Destroy and end the container.
Docker compose is a tool to define and run many docker container applications at once. Docker compose uses a YAML file to setup a docker application and configuration. Docker compose can be executed in all environments namely testing, development etc., Docker compose contains the control to manage the entire lifecycle of any application built. User can start/stop/restart all the available services, can monitor the services running and can create a log file of the output for the services running.
- Docker-compose also uses a project name as an identity and is capable of running many numbers of distinct environments over one host.
- Docker compose saves the volume of data. While running the docker compose up command, it monitors the status of the docker container. If it finds any container running before, it transfers the volume of data from the previous container to the newly created container thereby saving data.
- Docker compose uses cache memory to form a docker container thereby using the previously prevailing containers again. Because of this feature, a developer could be able to change the application environment easily.
- Docker compose allows variables for several environments or multiple users more flexibly using compose file.
To install the Docker Engine on implied hosts, we need a specific tool called Docker machine. User can control the implied hosts through commands passed from the Docker machine. Docker machine also provides swarm clusters for Docker.
Before the emergence of Docker, other container technologies ruled the era in cloud space. After Docker’s existence, other technologies started to downfall because of the Docker’s excellent features. Docker does not need any pre-defined infrastructure unlike other container technologies. Docker runs on any cloud even in any one’s laptop. Docker containers allow multiple environments over a single host. Docker containers save volume data space by reusing the previous docker containers. It is also become the popular and best technology for documenting in the containerization methodologies.
To start/stop the daemon process, the following commands were used:
Service docker start – to start the daemon process Service docker stop – to stop the daemon process
To do that, the following syntax is to be used.
Nsenter –m –u –n –p –i –t container ID command where -u refers to the UTS name space -n refers to the name space of the network -p refers to the name space of the process -m refers to the name space of mount -i is used to work the container to be run in the interactive mode -t helps to establish connection to I/O streams present in the container to the host Container ID – ID refers to the container Command – to run the container
Say for example, the returned value may be: sudo nsenter –m –u –n –p –i –t 4567 /bin/bash
Docker has a list of instruction commands that are present in a docker file. They are:
Docker contains several storage drivers through which enables the user to work with the storage devices. The following are some of the storage drivers used in docker:
AUFS: AUFS is a firm driver. If the production team is ready for production activity, AUFS is a perfect driver for that kind of applications.
AUFS uses its memory very well and helps to preserve space in the containers. AUFS suits well for service oriented applications as well. This driver consumes high write access.
Overlay Driver: Overlay is also a firm driver and uses memory good like AUFS. This driver well suits for laboratory testing applications.
Btrfs: This driver is used to perform primary functions of Linux kernel. This driver consumes high write access. In case of controlling several build pools, this driver suits well.
ZFS: This is also a firm driver and suits well for laboratory testing applications like overlay driver. ZFS suits well for service oriented applications like AUFS.
Device mapper: Another important storage driver is Device mapper, provides enhanced Docker experience to the developers and is a firm driver. Device mapper suits well for service oriented applications like AUFS and ZFS. This driver is used to perform primary functions of Linux kernel.
Docker contains distinct volumes that are divided among the containers. These distinct volumes are called as data volumes. The following are some of the features of data volumes:
- Data volumes starts to operate once the container is formed.
- These data volumes can be divided among multiple containers and also can be used again in the containers.
- Any changes made to the data volume will be immediately reflected.
- Data volumes cannot be destroyed. They prevail though the container is deleted.
A programmer could be able to change the storage driver for a container using the following command.
sudo docker run –d –volume-driver=flocker -v /home/demo:/var/Jenkins_home – p 5600:5600 –p 80000:80000 jenkins
The volume-driver feature allows to change the storage driver for a container. To assure whether the storage driver is changed or not, user can use docker ps command. After this docker ps command, we have to use docker inspect command to verify the storage driver is changed.
sudo docker ps sudo docker inspect 8affghbedg1kh>tempvar.txt
Docker volume can be created using the following syntax:
Docker volume create –name=volumename –opt options
The above syntax creates 100MB size volume with some name given. We can list all the docker volumes using the following syntax:
Docker volume 1s
Docker host and Linux host communication can be established using networking. Through Docker networking, one container could be able to communicate with another and also with the host. The bridging between docker host and linux host can be filled by identifying the “ipconfig” on the docker host. This command will let you know the ip address of the
docker host. This Ethernet adapter will be created while docker is installed in the docker host.
Before starting the containers, Docker network has to be created. Docker network can be created using the following syntax:
docker network create –driver drivername name where
driver name – is the name of the created network driver name – name of the network
For example, the command may be:
sudo docker network create –driver abc recent_efg
This created network has to be attached to the container while launching it.
sudo docker run –it –network=recent_efg ubuntu:latest /bin/bash
Later, we can check whether the container is attached to the newly created network.
sudo docker network inspect recent_efg
Node.js is a widely accepted and famous framework among the developers to develop server side applications. It is a frame work in Java script and is available open source which runs on various OS. Since Node.js become popular, Docker assures better support for the developers to use it in Docker.
MongoDB is a well known and widely accepted database by IT professionals for development. Recent day web apps are built using MongoDB data base. Because of its popularity, Docker ensures support to MongoDB to be used with it.
NGINX is a well known user friendly web app that can be used in the server side to develop web applications. NGINX is available open source at free of cost. This web server is designed to operate in wide variety of OS. Because of its demand and growing popularity, Docker also ensured its support to NGINX web server.
Docker cloud is an additional support provided by docker through which the developer could perform several operations. They are:
- Nodes: Through Nodes, the user can connect Docker cloud to the already prevailing clouds such as AWS. Azure etc., through which containers can spin on top on these cloud environments.
- Uninterrupted integration: Through this feature of Docker cloud, the user can communicate with Github to avail uninterrupted services one after the other sequentially.
- Software Deployment: Through this, the user can start an application and docker containers.
- Cloud Repose: In Cloud repose, an user can keep repositories created by them.
- Uninterrupted Deployment: User has the facility to automate their applications.
docker login – Through this syntax, user can enter their credentials to login their own cloud repositories.
Docker supports logging options through which a developer could troubleshoot errors easily once it is occurred. Logging could be at Daemon level or at Container level.
Logging at Daemon Level
Daemon logging has four levels of logging namely Debug, Info, Errors and Fatal. Debug carries all the information happened in the daemon process. Info carries the errors occurred during the daemon process. It also carries all other information during the daemon process. Errors contain the errors happened during the daemon process. Fatal lists the fatal errors happened during the daemon process.
Logging at Container Level:
- Docker also allows logging at the container level. It can be done using the following command:
- sudo docker run –it ubuntu /bin/bash
- After this command, use docker log command with the specific ID of the container to check the containers for errors.
- Sudo docker logs 45dfgh6asdf
Jenkins is the most popular continuous integration tool used by developers to create web applications. Docker allows and supports many continuous integration (CI) tools and Jenkins is one among them. Jenkins contains enough plugins to access the containers. Docker has a separate plugin for the Jenkins tool.
Kubernetes is a special supporting feature to be used with Docker. This framework allows Docker containers to establish communication with the real world. Kubernetes allows Docker containers to establish multiple services at a time. Let’s say for an example, assume we contain two services, among which one service contain mongoDB and NGINX and other service contain REDIS and NGINX. Among these services, an IP is distributed through which they can be connected with other applications in the real world. Kubernetes can control all these services.
- Users can easily configure and converse with Docker.
- User-friendly interface and Open source environment.
- Efficient and flexible scripts can be built with version interchange features.
- The primary setup is very easy.