Intermediate Docker Interview Questions and Answers

15. Can You Tell the Difference Between CMD and ENTRYPOINT?

CMD vs ENTRYPOINT

• CMD is used for setting default commands and arguments that will be executed at the start of runtime of the containers. It is oftenly overridden by providing command-line arguments during container startup.
• ENTRYPOINT configures a container to run as an executable, defining the command that has to be executed when the container starts. It is more strict than CMD and is oftenly used when the container should have to behave like an executable.

Know more about CMD vs ENTRYPOINT.

16. What are the Key Distinctions Between Daemon Level Logging and Container Level Logging in Docker?

Daemon Level Logging vs. Container Level Logging

• Daemon Level Logging: It involves with configuring the Docker daemon’s logging behavior globally. This will affect all containers that are running on the host. Configuration settings will be applied at the daemon level.
• Container Level Logging: This will be connected to logs specific to an individual container. They can be accessed using the docker logs <container_id> command , providing clear understanding regard the container’s runtime activities.

docker logs <container_id>

17. What Does the Docker Info Command Do?

docker info provides detailed information regarding the Docker system. It includes information such as the number of containers, images, storage driver that are used and much more. It’s a valuable command for gaining details on overview of the Docker environment.

18. Where are Docker Volumes Stored in Docker?

Docker volumes will be stored on the host machine in the directory /var/lib/docker/volumes . This ensures persistance of the data storage even if the container is removed.

19. Can You Tell the Differences Between a Docker Image and Layer?

A Docker Image can be considered as a snapshot of a file system and application dependencies. It is composed of multiple layers, where each layer will represent a set of filesystem changes. These Layers facilitate in efficient image creation and sharing common components among the images.

20. Can a Container Restart By Itself?

Yes, a container itself can restart automatically by setting up the –restart option during the creation period of time. For example using `docker run –restart` always. This will ensure that the container restarts irrespective of its exit status.

docker run --restart

21. Name the Essential Docker Commands and What They Do.

The essential Docker Commands are listed here:

• docker run: Docker run command is used to run the docker image as a docker container.
• docker ps: Docker os command will list all the running container in the docker.
• docker exec: It helps in execute the commands in a running container.
• docker stop: It will stops a container which is running in the docker.

22. What are Docker Object Labels?

Docker object labels are key-value mapping pair applied to the docker objects for better organizational and metadata purposes. For example, `docker run –label environment=production <image_name>` adds a label to a container.

docker run --label environment=production <image_name>

23. How Do You Check the Versions of Docker Client and Server?

Use `docker version`command to obtain the detailed information about the Docker client and server, including their respective version numbers.

docker version

24. Why is Docker System Prune Used? What Does It Do?

`docker system prune` is used for removal of unused data on inclusion of stopped containers, docker networks, and dangling images. It helps in freeing up the disk space on cleaning unnecessary resources.

docker system prune

25. What is Docker Swarm?

Docker Swarm is an inherented native clustering that comes up with a orchestration solution for the Docker software. It helps in simplifying the management of a swarm of Docker nodes on allowing the seamless scaling of the applications across various multiple nodes within the network. It provides built-in load balancing and will ensure the high availability of containerized applications.

26. How Do You Scale Docker Containers Horizontally?

Horizontal scaling is achieved through replicating the services across multiple nodes. Tools like Docker Compose or Docker Swarm facilitate this process. For example, using `docker-compose up –scale web=3` command will replicates the “web” service to three instances, distributing the workload across them horizontally.

docker-compose up --scale web=3

27. What Is the Difference Between Docker Restart Policies “no”, “on-failure,” And “always”?

These restart policies will provide flexibility in managing the container behavior based on specific requirements. The restart policy “no” gives full control over restarts, “on-failure” handles irregular issues, and “always” will ensures the constant availability. Choose the appropriate policy based over the nature and importance of that particular containerized application.

28. How Do You Inspect the Metadata of a Docker Image?

By using the `docker inspect <image_name>` command , you can examine into detailed metadata about the Docker image. This contains the information regarding labels, layers, and the configuration settings.

docker inspect <image_name>

29. How Do You Limit the CPU and Memory Usage of a Docker Container?

Om using the –cpus option you can set the CPU limits and with -m option you can set memory limits. The following example illustrates usuage of CPU and memory for a docker container.

docker run --cpus=3 -m  1024M   <image_name>

30. What are the Differences Between Docker Community Edition (CE) and Docker Enterprise Edition (EE)?

Usage of Docker Community Edition will be peferable for individuals and small-scale projects, It provides the essential features of containerization for free. On the other hand, Docker Enterprise Edition deals in providing the enterprise needs with advanced features and support for the large-scale projects in production environments. The choice between these two will depends on the scale, requirements, and support needed for the Docker deployment.

Docker is an open-source platform designed to automate the deployment, scaling, and management of applications in lightweight containers. Docker is a leading containerization platform that has revolutionized the way applications are developed, shipped, and deployed. Known for its efficiency, scalability, and ease of use, Docker has become an essential tool in the tech stack of many top companies, including Uber, Airbnb, Google, Netflix, Instagram, Spotify, Amazon, and many more. Its ability to create, deploy, and run applications in containers makes it a go-to choice for modern DevOps practices.

In this article, we have compiled a list of 50+ Docker interview questions and answers. These questions cover a wide range of topics, from the basics of Docker containers to more advanced concepts such as container orchestration, Docker Compose, and Docker networking. Whether you’re a beginner exploring containerization or an experienced professional (5 years or 10 years of Experience) preparing for a Docker-focused interview, this guide equips you with the insights and knowledge necessary to succeed in your Docker interview.

Docker containers are lightweight a single server or ( Virtual Machine ) VM can run several containers simultaneously. It implements a high-level API to provide these lightweight containers that run processes in isolation. The magic of docker lies in making the process as containers ( Operating system ) by providing separate namespaces, security groups, and unique hostnames.

Docker comes up with popular tools such as docker-compose for defining and running, docker swarm providing the native functionality for docker containers and docker volume facilitating independent persistence of data.