Docker made a splash in the Tech industry when it was introduced in 2013. It quickly became a huge success, with over 8 billion container image downloads by the end of 2017 (just in 4 years). Job opportunities increased exponentially as the demand for docker increased. In 2023, Docker has become a fundamental tool in a professional programmer's life, as per the StackOverflow Developers Survey 2022 results.
In the category of other tools npm and Docker come at the top and are used by programmers apart from programming languages, and libraries. Docker and Kubernetes are becoming industry standards when it comes to containerization and managing the containers.
So if you are planning to appear for an interview for Software development, DevOps, or Backend Development, you must have a basic understanding of Docker, so do learn Docker before the interview.
Frequently Asked Docker Interview Questions
In this article, we have compiled a list of some 15 commonly asked questions to help you gain a basic understanding of Docker.
Before moving on, here is a video to help you understand all about Docker.
Now let's move on to the questions.
Q1: What is Docker?
Docker or Docker Engine is a software that helps us manage the lifecycle of containers, define how they will be set up, what applications/software/services they will run inside them, their networking requirements, their storage requirements, and if required how to easily destroy a container and start afresh.
Docker uses docker images to run processes inside the container. We can create a DockerFile in which we can define installation steps for the application, which may include,
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setting up the environment,
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installing and running necessary services,
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pulling code or the build from your build server,
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importing the dependency,
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setting up the database,
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and finally running the application.
So, if you have Dockerised your application, which means if you have made a Docker version of your application setup, then you can run your application anywhere. All you need is a Docker installed and the correct Docker image to automatically run all the steps and run your application.
This ensures that the application will always perform identically regardless of the environment in which it is running.
Q2: Why is DevOps Necessary?
Earlier, businesses used to work on a large set of new features in a single release cycle, where those features were developed, tested, and then released together. But that was time-consuming because, in that case, even a small important fix would have to wait for the common release date. But that's not the case anymore.
Now with DevOps, businesses have updated their software development lifecycle and started to move towards CI/CD which stands for Continuous integration and continuous delivery, which means, that as a new feature is developed and tested, it is integrated to the main build and delivered to the customer, and this process keeps on running.
This provides a number of benefits, including faster customer feedback, higher software quality, and increased customer happiness.
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Increase the frequency of deployment
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Each release has a lower failure rate
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Time to recovery is reduced in the case of a new release crash because each release branch has fewer code changes overall.
Q3: How Can We Use Docker to Create Environment-Agnostic Systems?
Docker allows you to package your application and its dependencies together, and deploy them inside a container anywhere. For this, Docker relies on the following features:
- Docker containers
- Images and DockerFile
- Volumes
- Environment variable injection
- Read-only file systems
Q4: Is it Possible to Determine The State of a Docker Container?
By using the command, we can determine the state of a Docker container.
docker ps -a
This will then show all accessible docker containers on the host along with their associated statuses. From there, we can quickly find the container of interest and ascertain its state.
Q5: What Are The Benefits of DevOps?
Technical advantages:
- Continuous supply of software
- Simpler issues to resolve
- Rapid resolving of issues
Benefits to business:
- Enhanced feature delivery
- More stable operating environments
- More time available for value creation (rather than repair/maintenance)
Q6: What Are The Most Frequently Used Dockerfile Instructions?
Several popular Dockerfile directives include the following:
- FROM: We utilize FROM to provide a starting point for following commands. FROM is the first instruction in every valid Dockerfile.
- LABEL: We use LABEL to categorize our photos according to the project, module, and license requirements. Additionally, we may utilize LABEL to aid with automation.
- LABEL: It specifies a key-value pair that may subsequently be used to manage the Dockerfile programmatically.
- RUN: The RUN command is used to run any instructions in a new layer above the currently shown picture. Each RUN command adds something to the image that will be used in the following phases of the Dockerfile.
- CMD: We use the CMD command to set the default settings for a container that is currently running. When numerous CMD commands are included in a Dockerfile, only the final instruction is utilized.
Q7: What Different States May A Docker Container Be in at Any One Time?
At any moment in time, a Docker container may be in one of four states. These states include the following:
- Running
- Paused
- Restarting
- Exited
Q8: What is a Docker Container?
Docker containers contain the program and all of its dependencies, but share the kernel with other containers, executing in userspace on the host operating system as independent processes. Docker containers are not infrastructure-dependent; they operate on any machine, any infrastructure, and in any cloud.
Q9: Specify Docker hub.
It is a cloud-based registry service that allows you to connect to source code repositories, produce and test images, store images uploaded manually, and connect to Docker cloud for image deployment to your hosts. It serves as a centralized repository for the discovery, distribution, and management of container images, as well as for user and team communication and pipeline automation.
Q10: What is a Docker image?
Docker image is the container's source code. In other words, containers are created using Docker images. When the build command is used to create images, they will generate a container when run is used to start them. Docker images are saved in a registry, for example, registry.hub.docker.com. Because pictures may become fairly big, they are meant to be constructed of layers of other images, requiring just a little amount of data to be sent when images are transferred over a network.
Q11: How are the COPY and ADD commands in a Dockerfile Different?
Although ADD and COPY are functionally equivalent, COPY is often preferable.
That is because it is more transparent than attention deficit disorder. COPY enables simply the basic copying of local files into the container, but ADD includes additional functionality that are not immediately apparent (such as local-only tar extraction and remote URL support). As a result, the optimal application of ADD is for auto-extraction of local tar files into the image, as in ADD rootfs.tar.xz /.
Q12: How does a CI (Continuous Integration) server work?
The purpose of the continuous integration server is to continually integrate all changes made and committed to the repository by various developers and to check for compile faults. It should build code numerous times a day, ideally after each change, so that it can determine which commit caused the breakdown if one occurs.
Q13: Which Application Types - Stateless Or Stateful - Are Better Suited to Docker Containers?
It is advisable to construct stateless Docker applications. We can create a container for our application and extract the application's configurable state parameters. Now, we can run the same container with various settings in Production and QA environments. This enables the reuse of the same image in many circumstances. Additionally, a stateless application scales much more easily than a stateful application using Docker Containers.
Q14: Describe the Fundamental Docker Process.
- The Dockerfile is where it all begins. The Dockerfile contains the Image's source code.
- After creating the Dockerfile, you build it to produce the container's image. The image is just the "compiled version" of the Dockerfile's "source code."
- Once you've obtained the container's image, you should distribute it through the registry. The registry operates similarly to a git repository in that photos may be pushed and pulled.
- The image may then be used to run containers. A running container is extremely similar to a virtual computer in many ways (but without the hypervisor).
Q15: How will Docker in Production be Monitored?
Docker offers tools for monitoring Docker in production, such as docker stats and docker events. These instructions enable us to get reports on critical statistics.
- Docker stats: When we use docker stats with a container id, we obtain information about a container's CPU, memory utilization, and so on. It is comparable to Linux's top command.
- Docker events: Docker event is a command that displays a stream of Docker daemon activity.
Docker events include attach, commit, die, detach, rename, and destroy. Additionally, we may utilize a variety of tools to restrict or filter the events in which we are interested.
Conclusion
This concludes the post on Docker Interview Questions. With increased commercial competitiveness, businesses have recognized the critical need of adapting to and capitalize on changing market conditions. Several factors kept them in the game, including quicker system scalability, improved software delivery, and adaptation to new technology. That's when docker stepped in and boosted these firms' chances of continuing the contest.
