Prepare for your next DevOps interview with these top 50 Docker interview questions, designed to help you understand and master Docker's core concepts and practices.
Docker is an open-source platform that automates the deployment, scaling, and management of applications in lightweight containers. It allows developers to package applications with all their dependencies, ensuring consistency across multiple environments.
Docker containers are lightweight, portable, and self-sufficient units that include everything needed to run a piece of software, including the code, runtime, libraries, and system tools. They can run on any platform that supports Docker.
Docker Hub is a cloud-based repository where Docker users can create, test, store, and distribute Docker images. It provides a centralized resource for container image discovery and sharing.
Docker containers share the host system's kernel and resources, making them more lightweight and faster to start compared to virtual machines, which require a full OS installation. VMs have their own operating systems and are more resource-intensive.
A Dockerfile is a script containing a series of instructions on how to build a Docker image. It includes commands for specifying the base image, installing dependencies, copying files, and setting up the environment.
Docker Compose is a tool used for defining and running multi-container Docker applications. It uses a YAML file to configure application services, networks, and volumes, allowing users to start and manage all containers with a single command.
Docker Swarm is Docker's native orchestration tool that enables users to create and manage a cluster of Docker nodes as a single virtual system. It provides features for scaling, load balancing, and service discovery.
You can create a Docker container using the `docker run` command followed by the image name. For example, `docker run -d nginx` will create and start a container from the Nginx image.
Both `ADD` and `COPY` commands are used to copy files from the host to the Docker image. However, `ADD` can also extract TAR files and download files from URLs, whereas `COPY` is simpler and preferred for just copying files and directories.
Docker provides several commands for monitoring containers, such as `docker stats` for real-time metrics and `docker inspect` for detailed information about a container. Additionally, tools like Prometheus, Grafana, and ELK stack can be used for advanced monitoring and logging.
A Docker image is a read-only template used to create containers. It includes the application code, libraries, dependencies, and the operating system needed to run an application. Images are built using Dockerfiles.
To list all running Docker containers, use the command `docker ps`. To list all containers, including stopped ones, use `docker ps -a`.
A Docker volume is a mechanism for persisting data generated by and used by Docker containers. Volumes are managed by Docker and can be shared between containers, making them useful for maintaining data across container restarts.
The `docker pull` command is used to download a Docker image from a registry, such as Docker Hub. For example, `docker pull ubuntu` will download the latest Ubuntu image.
You can remove a Docker container using the `docker rm` command followed by the container ID or name. For example, `docker rm container_id`.
The `docker exec` command allows you to run a command inside a running Docker container. For example, `docker exec -it container_id bash` will open a bash shell inside the specified container.
To stop a running Docker container, use the `docker stop` command followed by the container ID or name. For example, `docker stop container_id`.
Docker networking allows Docker containers to communicate with each other and with other external systems. Docker provides several network drivers, such as bridge, host, and overlay, to manage container networking.
The `docker build` command is used to build a Docker image from a Dockerfile. It includes all the instructions and context needed to create the image. For example, `docker build -t myimage .` will build an image with the tag `myimage` from the Dockerfile in the current directory.
A Docker registry is a storage and distribution system for Docker images. Docker Hub is the default public registry, but you can also use private registries like AWS ECR, Google Container Registry, or host your own registry using Docker Registry.
To restart a Docker container, use the `docker restart` command followed by the container ID or name. For example, `docker restart container_id`.
Docker images are read-only templates used to create containers, while Docker containers are running instances of these images. Images are used to define the application's environment, and containers are used to run the application.
To update a running Docker container, you typically need to create a new image with the desired changes and then deploy a new container from that image. You can use the `docker commit` command to create a new image from the current state of a container, but this is not a best practice for updating containers.
Docker Compose is used to define and manage multi-container Docker applications. It allows you to specify the services, networks, and volumes required for your application in a single YAML file, making it easy to start and manage complex applications.
In Docker Swarm, you can scale services using the `docker service scale` command followed by the service name and the desired number of replicas. For example, `docker service scale myservice=3` will scale the service `myservice` to three replicas.
A Docker namespace provides isolation for containers, allowing them to have their own view of the system's resources. Namespaces are used for process isolation, network isolation, and file system isolation.
To remove a Docker image, use the `docker rmi` command followed by the image ID or name. For example, `docker rmi image_id`.
The `docker tag` command is used to create a new tag for an existing Docker image. This is useful for versioning images and organizing them in registries. For example, `docker tag image_id myimage:v1.0`.
To create a Docker network, use the `docker network create` command followed by the network name. For example, `docker network create mynetwork` will create a new network called `mynetwork`.
A bind mount is a way to map a directory on the host system to a directory in a container, while a volume is a Docker-managed storage that is more flexible and portable. Volumes are recommended for persistent data storage because they are managed by Docker and can be shared between containers.
To copy files from a Docker container to the host, use the `docker cp` command followed by the container ID or name, the source path inside the container, and the destination path on the host. For example, `docker cp container_id:/path/to/file /host/path`.
Docker Engine is the core component of Docker, responsible for creating and managing containers. It includes the Docker daemon, a REST API, and a command-line interface (CLI) that allows users to interact with Docker.
Docker layers are the building blocks of Docker images. Each instruction in a Dockerfile creates a new layer, which is a read-only snapshot of the file system. Layers are stacked on top of each other to form a complete image, and they are shared between images to save space and speed up builds.
To view the logs of a Docker container, use the `docker logs` command followed by the container ID or name. For example, `docker logs container_id`.
The `docker inspect` command provides detailed information about Docker objects, such as containers, images, networks, and volumes. It returns the object’s configuration and state in JSON format.
To run a Docker container in the background, use the `-d` option with the `docker run` command. For example, `docker run -d nginx` will start an Nginx container in detached mode.
A Docker secret is a way to securely manage sensitive data, such as passwords and API keys, in Docker Swarm. Secrets are encrypted and only accessible to services that need them.
To list all Docker images on your system, use the `docker images` command.
Both `CMD` and `ENTRYPOINT` specify the command to run when a container starts. `CMD` provides default arguments for the `ENTRYPOINT` instruction, but it can be overridden by passing arguments to `docker run`. `ENTRYPOINT` is not overridden and is used to define the main command to run in the container.
To create a Docker image from a container, use the `docker commit` command followed by the container ID or name and the new image name. For example, `docker commit container_id new_image_name`.
The `docker network ls` command lists all the networks that are created on the Docker host.
To stop all running Docker containers, use the command `docker stop $(docker ps -q)`.
Docker multi-stage builds allow you to use multiple `FROM` statements in a Dockerfile to create intermediate images, which can help reduce the final image size by copying only the necessary files from the intermediate images to the final image.
To remove all stopped Docker containers, use the command `docker container prune`.
The `docker push` command is used to upload a Docker image to a registry, such as Docker Hub. For example, `docker push myimage:tag` will push the image `myimage` with the specified tag to the registry.
To restart the Docker daemon, use the command `sudo systemctl restart docker` on systems using systemd, or `sudo service docker restart` on older systems.
Docker service discovery is the process of automatically detecting and connecting services within a Docker Swarm cluster. Docker Swarm uses an internal DNS server to resolve service names to container IP addresses, allowing services to communicate with each other.
To view resource usage statistics of Docker containers, use the `docker stats` command, which provides real-time metrics for CPU, memory, network, and disk I/O usage.
A Docker context is a configuration that allows you to switch between multiple Docker environments, such as different Docker hosts or cloud providers. You can use the `docker context` command to create, list, and switch contexts.
You can limit resource usage for a Docker container using various options with the `docker run` command. For example, `--memory` to limit memory usage, `--cpus` to limit CPU usage, and `--blkio-weight` to control block I/O weight.
Published By: Krishanu Jadiya
Updated at: 2024-07-27 15:15:17
