When we imagine a ship, we cannot possibly ignore the rudder. Similarly, when we think of DevOps, we are bound to include Docker within the purview of our thoughts. Given that the future scope of DevOps has expanded ever so widely in the contemporary context, it is imperative to understand what are the bases upon which DevOps relies on.
A fair analogy between Docker and DevOps would be, the foundation of a building and the different stories of the same building. Essentially, Docker is the platform upon which DevOps is built. Most automation driven technologies, which in turn is all-pervasive in the modern times, require a seamless channel of building and distributing software applications as well as consistently maintaining these applications in order to troubleshoot any errors that may arise.
This is precisely where Docker becomes an asset to the developers. Therefore, increasingly, business enterprises are attempting to integrate Docker within their technological bandwidth to ease out operations and include more scope of automation within the system. No wonder then, as the demand for Docker-based programming grows, the demand for programmers with knowledge and expertise in Docker will also rise in direct proportion.
Most interviews for DevOps and software development these days entail one or more questions on Dockery. Hence it is advisable to brush up your Docker skills when trying for a new DevOps role. Read on to find some of the most commonly asked interview questions concerning Docker!
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Docker Interview Questions & Answers
1. Would you say that Docker is significant today? Why or why not?
Docker comes handy in incorporating numerous software applications within one system, be it a virtual machine or physical hardware. This, in turn, enables a single developer to add different dimensions to the application and manage multiple aspects of the application from a single unit. Consequently, Docker has been enjoying a widespread client base which even includes some big names. To illustrate the reason behind this popularity, let’s take the example of a common electronic wallet.
The app that enables you to shop, pay bills and transfer funds at a mere touch of a tab entails a whole range of complicated programming. Often such dynamic apps include different elements, scripted in different programming languages or could also be an amalgamation of three different applications coded in the same language. Typically, this will only run if a specific type of machine that can host multiple applications is available.
But since the availability of such machines is rare and far between, most developers resort to Docker to come up with a viable solution. Docker provides a single host to the operating system which can, in turn, support multiple applications and their respective libraries and dependencies. This is indeed a pioneering solution that empowers businesses to expand their innovation in a cost-effective way.
Hence, while appearing for a tech-based interview, if one is able to woo the recruiters with their aptitude in Docker, then one automatically gains ground over the others.
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2. Why do we need Docker?
As explained in the example above, web applications usually include their own set of libraries and dependencies. Accordingly, it becomes difficult to run them in different environments and club them along with associated applications for advanced levels of DevOps. As a solution to this conundrum, Docker offers a platform that can integrate the different applications along with their libraries and dependencies within a virtual container.
This enables several container packages to run simultaneously on a single machine. It provides an ideal environment for consistent development, testing, and deployment. Docker has emerged as an indispensable tool for DevOps engineers.
3. What are the advantages of Docker?
A unified platform that packages all the elements of an application and containerizes them in order to facilitate fluidity of production and deployment environment is indeed a Godsend for all developers. This is why Docker has consistently enjoyed immense popularity in the domain of software development. It comes with a concrete set of advantages which in turn facilitates more agile and intuitive application development and is integral to advances in the field of DevOps.
- Multiple applications with diverse specifications and requirements can be hosted in a singular platform with the help of Docker. The only clincher here is that the applications must have compatible operating system requirements.
- Docker offers optimized storage. As a result, numerous applications can be stored together and all this without exhausting a lot of disk space. This is the beauty of a Docker container that it incorporates a whole gamut of applications within only a few megabytes.
- By clubbing together different applications on a unified platform, Docker facilitates continuous and prompt software delivery.
- Yet again, containerized solutions like Docker are highly useful in the early detection and easy resolution of problems.
- Had it not been for Docker, the only possible method to deploy multiple applications simultaneously would be a virtual machine with the capacity to host different applications. But this would require a huge memory space. As a robust alternative, Docker containerizes the applications and does this without any inbuilt operating system. But rather runs on the destination operating system of a single machine. This enhances efficiency and helps in saving a significant volume of memory space.
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- From a business point of view, this can entail a huge amount of advantages. Firstly, easier deployment directly translates to faster delivery of software features and upgrades. Consequently, not only can enterprises cater to more clients within a shorter span of time but also constantly upgrade their services to appeal to new clients.
- Since the hardware requisites of running multiple applications can be reduced by using Docker, it goes a long way in reducing the costs of businesses. Businesses are able to add value to their products in a far more cost-efficient manner by using Docker.
4. Are there any drawbacks to using Docker?
Despite the whole gamut of advantages, there is one hurdle to the deployment and management of Docker. This revolves around the operating system compatibility requirements. Only applications that have the same operating system compatibility can be containerized together with Docker. This entails serious limitations on the type and number of applications that can be packaged and run within the scope of Docker.
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5. What does a Docker container comprise of?
A Docker container typically consists of an application along with all its libraries and other dependencies. A Docker container functions by sharing the kernel with several other containers that share the space on a given host operating system. Docker containers may run anywhere, irrespective of the environment.
It doesn’t require any specific infrastructure. It can run both on a physical computer system or a virtual machine like any cloud computing infrastructure. One may imagine a Docker container as the runtime instance of a Docker image.
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6. What is meant by a Docker Image?
The best way to explain the relationship between a Docker image and a Docker container would be to draw a comparison between a blueprint and the actual building. Docker image is effectively the blueprint to the Docker container.
It is based on the Docker image that a Docker container is created. Once a Docker image is run by a user, an instance Docker container gets created. These images are made using the build command and can then be deployed in any Docker based environment.
7. How does Docker help in building environment-agnostic systems?
The USP of Docker is that it doesn’t not have any infrastructure specifications. It can run on any system, irrespective of the environment. This is made possible by three main attributes of Docker. The read only file systems, volumes and the environment variable injection are the three features of Docker that help in building environment agnostic systems.
8. What is a Docker Hub?
As we understand, Docker containers are built upon the instances of a Docker image. Just as the Docker containers are stored on the kernel of a given operating system, Docker images also need a place to reside per se. This registry or a collection of Docker images is popularly called the Docker Hub. The Docker Hub is a publicly available repository of Docker images where the users can access a Docker image and create customized Docker containers.
Docker Hub stores Docker images because these images can potentially be of a large size and make it cumbersome to transfer the file from the repository to the user’s system. To avoid that the images contained in the Docker Hub are composed of layers of other images. Consequently, when a transfer takes place, only a small amount of data is sent across the network.
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9. What is the Docker Architecture made up of?
Docker is made up of three main components all of which cumulatively make up the Docker Engine, which in turn is the core of the Docker Architecture.
Docker Engine is essentially a client-server application that is the driving force of the Docker platform. The Docker Engine looks after the overall functioning of the Docker containers. It consists of three vital elements.
The first element of a Docker Engine is a server which is basically a process that runs a command called the Daemon Program. It is what creates and manages every part of the Docker platform ranging from the containers, the images, the volumes, and the networks.
The next component of the Docker Engine is the REST API. The REST API delineates the functionalities of the server. It instructs the Server about the tasks at hand and lays down how the interaction between the application and the server is to be conducted.
Finally, we come to the final element of the Docker Engine, i.e. Client. The Client acts like a bridge between the user and the Docker platform. It is a command-line interface that facilitates all forms of the interface between the users and the platform.
10. What is a Dockerfile?
We understand that the Client element of a Docker Architecture allows the users to interact with the platform using line commands. This line command comes in the form of a text document that a user can call on in order to assemble a Docker image.
This text document is nothing but a Dockerfile. The Dockerfile consists of instructions by reading which Docker can automatically build images. Using the Dockerfile, Docker is able to execute various command line-instructions that can run in succession.
11. Can you provide the examples of some common Dockerfile instructions?
Dockerfile is a huge collection of Docker commands. However there are some basic instructions which must be invoked every time in order to use Docker.
The most common Dockerfile instruction is “FROM”. FROM is used to create the base image for any Docker image instance. It happens to be the first instruction in a given Dockerfile.
Since a large number of DevOps engineers use docker to build automation, another commonly used Dockerfile instruction is ‘LABEL”. LABEL comes handy in organizing the Docker images according to the requirements of the particular project, available licensing or module. Using LABEL, one can define a key-value pair which in turn helps in handling a Dockerfile programmatically.
RUN is yet another popularly used Dockerfile instruction that is used to effectively upgrade a Docker image. This command can be used when one wants to execute any particular instruction on a different layer on top of an existing image. The RUN command is used to add something additional to a current image and these are available for use in the subsequent steps in a Dockerfile.
Speaking of Dockerfile instructions one cannot help mentioning “CMD”. CMD is used to attribute a default value to any executing Docker container. However, if more than one CMD commands are used, the latest CMD command has an overriding effect over the rest of the commands.
12. What is a typical workflow in Docker?
Since the Docker containers are built from Docker images, a Docker workflow starts with the Docker image which in turn is in the Dockerfile. Dockerfile is created to provide the source code to the Docker Image. The Dockerfile source code is used to build the Docker Image. Once created, the Docker Image is distributed to a registry like the Docker Hub.
From the registry, the Docker image is run to finally create and execute a Docker container. Wherein starts the lifecycle of the Docker container. The lifecycle of a Docker container comprises creation, running, pausing or un-pausing, and then starting, stopping, followed by restarting, and finally being destroyed or killed.
13. How does Docker differ from other containerization methods?
Ease of usage and versatility are really the two factors that make Docker stand apart from other containerization methods. It can incorporate a large volume of discrete applications within the same hardware infrastructure when compared to any other containerization technologies. Docker is also very simple to deploy and easy to maintain for any DevOps professional. What is even more interesting is that Docker containers can be shared between different applications even.
14. What are some areas of application for Docker?
Docker provides effective solutions in simplifying configurations, enhancing debugging capacities, better management of code pipelines as well as isolating the applications. The multi tenancy feature is yet another area where Docker is utilized frequently.
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Which is better among Docker and Kubernetes?
Kubernetes and Docker are open-platform, cloud-based technologies, but there are differences between them. Docker technology deals with how to package applications within a container on a single node. On the other hand, Kubernetes technology is used to execute these containerized applications over a cluster. So, while Docker is for developing single containers, Kubernetes is used to manage and orchestrate a group of containers. Both can be implemented independently; for instance, larger organizations can benefit from adopting Kubernetes, smaller enterprises can suffice with using Docker. However, many organizations adopt both Kubernetes and Docker in combination to maximize the benefits of microservices development.
What is the difference between Docker images and containers?
Images and containers are two vital aspects of Docker technology. Images are the basic functional units in Docker, and everything revolves around these images. Docker images are basically read-only templates that are loaded with instructions for the deployment of containers. Images are either stored in the registry of Docker, such as Docker Hub, or a local registry. Containers instances of Docker images. These are actually virtual runtime environments that can help applications execute without being influenced by the supporting platform. The prime utility of Docker technology lies in its containers, which offer a lightweight, portable environment to deploy applications.
How is a container different from a virtual machine?
Virtual Machines and containers are basically resource vitalization technologies that share certain subtle similarities. However, the main difference between these two technologies is that virtual machines can be used to virtualize the whole machine, including its hardware layer. In contrast, containers can only be used to virtualize the application layer that exists above the level of the operating system. Containers are lightweight, portable, and constitute a robust ecosystem, which enhances the speed of application modification and deployment. Virtual machines offer a dynamic and interactive development platform and are totally immune to interferences by neighboring virtual machines. However, these are not as cost-effective and speedy in terms of performance as containers.