Top Docker Interview Questions and Answers for Your Interview Prep

Top tech companies set challenging Docker interview questions to assess your proficiency in building, deploying, and running applications. If you are applying for a Docker-specialized DevOps engineer position or a software developer position, be it a Java developer, a C++ developer, or a web developer coding in JavaScript, you will require expertise in Docker.

PayPal, Spotify, Uber, Netflix, and other Tier-1 tech companies use Docker to simplify the operations and make secure applications while bringing the infrastructure and security closer. Top companies receive thousands of applications for every software developer position. To outperform the competition, you must prepare strategically and cover all vital topics from the basic to the advanced level. The following top 30 Docker interview questions will help you uplevel your tech interview prep.

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Here’s what we’ll cover in this article:

• Docker Interview Questions and Answers
• Tough Docker Interview Questions for Experienced Developers
• Docker Interview Questions for Practice
• FAQs on Docker Interview Questions

Docker Interview Questions and Answers

To begin your tech interview prep, you must prepare the following common Docker technical interview questions and answers.

Q1. What is Docker?

Docker is an open-source containerization technology that has gained widespread popularity in the application packaging and cloud environment. You can use Docker to automate the deployment of applications in lightweight, portable containers.

Q2. What is a container?

A container defines a standard unit of software bundled with dependencies. It helps in deploying applications fastly and reliably between different computing platforms.

You can imagine Docker as a big ship (Docker) carrying huge boxes of products or containers. A container in Docker doesn’t need the installation of a separate operating system; rather, it utilizes the kernel’s resources and its functionality to allocate them for the CPU and memory.

Q3. What are the important features of Docker?

This is one of the important Docker interview questions. The primary features of Docker are as follows:

• Placement/affinity
• Application agility
• Easy modeling
• Version control
• Developer productivity
• Operational efficiencies

Q4. What are the main drawbacks of Docker?

Interviewers often ask Docker interview questions on the limitations you might face as a developer. Some common drawbacks of Docker are:

• It doesn’t provide a storage option.
• Docker has a poor monitoring option.
• There is no automatic rescheduling of inactive nodes.
• It has a complicated automatic horizontal scaling setup.

Q5. What is a Docker image?

You can use Docker images to create Docker containers. The build command helps create the Docker image, and every image is stored in the Docker registry.

Q6. What is the Docker engine?

Docker engine or daemon represents the server. You should run the docker engine and the clients on the same/ remote host, which can communicate through a command-line client binary and full RESTful API.

Q7. What are registries?

Docker has two types of registry:

• Public registry: Docker hub that allows you to store millions of images privately.
• Private registry: Allows you to share your custom base images within your organization while keeping a private and centralized source of truth for your architecture’s building blocks.

Q8. What do you understand by the term memory-swap flag?

Memory-swap in Docker refers to a modified flag that holds meaning only if- memory is also set. Swap enables the container to write express memory requirements to disk if the container ends up exhausting all the available RAM.

Q9. What is Docker Swarm?

A Docker swarm is used to convert a group of Docker hosts into a single, virtual Docker host. It offers a program interface to the standard docker application.

Q10. How do Docker clients and Docker Daemon communicate?

You can use the combination of Rest API, socket.IO, and TCP to communicate between the Docker client and Docker Daemon.

You must also practice the following basic Docker interview questions:

1. What are Docker object labels?
2. What are the steps for the Docker container life cycle?
3. What is Docker Trusted Registry?
4. What are Docker namespaces?
5. What are the components of Docker architecture?
6. What is a client?
7. What is a Docker host?
8. How does Kubernetes associate with Docker?

Tough Docker Interview Questions for Experienced Developers

If you are applying for senior positions, here are some interview questions on Docker for experienced individuals.

Q1. Which Docker commands will you frequently use while working with Docker? State their functions.

This is an important Docker interview question, and the interviewer can ask you questions on each of these commands specifically. The commonly used commands are as follows:

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Q2. What is the difference between virtualization and containerization?

The interviewers put up such Docker interview questions to indirectly gauge your understanding of the differences between virtual machines and Docker containers.

Q3. How is Continuous Integration (CI) and Continuous Development (CD) implemented in Docker?

This is one of the most important Docker interview questions. You can implement CI-CD in Docker in the following ways:

• You can run Jenkins on Docker.
• You can use docker-compose to run integration tests in Jenkins.

Q4. What is CNM?

CNM is the abbreviation for Container Networking Model. It is a standard from Docker, Inc. It forms the basis of container networking, and this approach provides container networking with support for multiple network drivers.

Q5. What is the lifecycle of a Docker container?

This is one of the essential Docker interview questions. The docker container lifecycle includes all the stages from its creation to its end. The crucial stages are:

• Created: It is when the container is just created new but not started yet.
• Running: The container runs with all its associated processes in this stage.
• Paused: It refers to the state when the running container has been paused.
• Stopped: This stage is when the running container has been stopped.
• Deleted: The final stage is when the container is in a dead state.

Q6. What do you understand about Daemon Logging and Container Logging?

This is one of the frequently asked Docker interview questions. Docker supports logging at two levels – Daemon and Container levels.

1. Daemon level

It is a kind of logging that has four levels:

• Debug has all the data about the happenings during the execution of the daemon process.
• Info has the information along with the error information during the implementation of the daemon process.
• Errors are those errors that occur in the execution of the daemon process.
• Fatal has fatal errors that occur during the execution.

2. Container Level

• You can use the following command for container level logging:
  sudo docker run –it <container_name> /bin/bash

• You can check for the container level logs using the following command:
  sudo docker logs <container_id>

Docker Practical Interview Questions for Practice

1. Would you lose data when the container exits?
2. How can you run multiple containers with a single service?
3. How would you configure the default logging driver under Docker?
4. How would you scale your Docker containers?
5. In what ways can you use insecure Docker image registries?
6. How can you change the default Docker network driver while running a Docker image?
7. When would you use container orchestration?
8. What do you understand about the possible states of Docker containers?
9. How will you ensure that container 2 runs after container 1 with Docker compose?
10. How would you run multiple copies of compose files on the same host?
11. Can you use JSON instead of YAML for developing the docker-compose file?

The above Docker interview questions will help you nail the most challenging interview rounds. You must practice these and learn the best strategies for effectively answering interview questions from mock interviews.

FAQs on Docker Interview Questions

Q1. What topics should I prepare for Docker interview questions?

You should be thorough on the topics related to network, containers, security, TLS, Kafka, event-oriented architecture, and microservices, in addition to basic and advanced Docker concepts to nail Docker interview questions.

Q2. How can I prepare for Docker interviews?

As a software engineer, you will have a few coding challenges for the interview. You must practice the various types of coding problems to ace these coding interview rounds. You should practice the most anticipated Docker interview questions to get well-versed in technical concepts related to Docker and behavioral questions (using the STAR method).

Q3. Which backend technologies are important for Docker interviews?

You should be adept at backend technologies like Java, Python, Node.js, Go, or C#/.NET to nail Docker interview questions.

Q4. Is my knowledge of Kubernetes helpful for a career in Docker?

Kubernetes is another useful container and orchestration technology that top tech companies value. Your knowledge of Kubernetes, in addition to Docker, can give you an upper hand in the interview process amongst other competitors.

Q5. What is the average salary of a senior software developer at Docker?

A senior software developer at Docker earns between $80k to $159k per year. The average salary is $114,480 annually (Source: payscale.com).

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