# Day 21 Task: Docker Important interview Questions ## **Docker Interview** ## Questions & Answers ### What is the Difference between an Image, Container and Engine? **Image vs Container vs Engine** **1 . Image:** Images are executable packages that contains application code, library and configuration files. **2 . Container:** A running instance of a image. Its isolated and lightweight with its own filesystem and processes. **3 . Engine:** The software that builds, runs and manage Container based on the images. ### What is the Difference between the Docker command COPY vs ADD? **Copy vs Add** **1 . Copy:** Docker copies files/directories from source to destination from host to local machine. **2 . Add:** It is similar to copy command, but it is also handle unpacking compressed file automatically. (eg: tar.gz) ### What is the Difference between the Docker command CMD vs RUN? **CMD vs. RUN** **1 . CMD:** It is the default command executed when the container starts. **2 . RUN:** Its executes the command during the image build process. It is mostly used for Installing dependencies, Setting up the environment, etc. ### How Will you reduce the size of the Docker image? **Reducing image size** **1 .** It is use for multi-stage builds the application in the temporary stage with unnecessary tools and then copy the final artifacts into the final images. **2 .** Leverage the base image with minimal dependencies such as Alpine Linux or Scratch, etc. ### Why and when to use Docker? **When to use docker** **1 .** Deploying micro-services architecture. **2 .** Standardizing the application environment. **3 .** Workflows with Continuous integration(CI) and continuous deployment(CD) in Jenkins. **4 .** Simplifying application deployment and testing. ### Explain the Docker components and how they interact with each other. **Docker Components and Interaction** **1 . Docker file** interact to provide instruction to build Docker images. **2 . Docker daemon** interact with Docker container to build and run them. **3 . Docker registry** interact with Docker images to store and share the container in private and public. **4 . Docker client** interact with user interface to communicate with Docker daemon. ### Explain the terminology: Docker Compose, Docker File, Docker Image, Docker Container? **Docker Terminology** **1 . Docker compose** is the tool which defines the running container with eases. **2 . Docker file** is the component its instruct to build Docker image. **3 . Docker image** is the blue print of container its contain application code, library and configuration file. **4 . Docker container** is the running instance of container which is isolated with its own filesystem and processes. ### In what real scenarios have you used Docker? **Real-world Docker Use Cases** **1 .** Running micro-service **2 .** Deploying web-application **3 .** Building and testing application in isolated environment. **4 .** Simplifying development workflows (DevOps) ### Docker vs Hypervisor? **Docker vs. Hypervisor** **1 . Docker** provide containerization, isolation process with the same OS kernel **2 . Hypervisor** create a virtual machine (VMs) with its own OS. Its offers strong isolation with more resource-intensive. ### What are the advantages and disadvantages of using docker? **Advantages of Docker** **1 .** Run the application across differnet environment. **2 .** Container share its own OS kernel but isolated with each other. **3 .** Easy deployment and scaling containerized application. **4 .** Streamlines the deployment and testing workflows. **Disadvantages of Docker** **1 .** Required proper security measure to minimize container escape risks. **2 .** It can impact to host system resource if not managed efficently. ### What is a Docker namespace? **Docker Namespace** Its is virtualized layer that isolates the process, file system, network resource, etc. ### What is a Docker registry? **Docker Registry** A repository for storing and sharing the Docker image. public registry like Docker hub or you can setup private registries. ### What is an entry point? **Entry Point** The command specified in Dokerfile's `ENTRY POINT` instructure that executed when the container starts. ### How to implement CI/CD in Docker? **CI/CD with Docker** Integrating docker into CI/CD pipeline that allows you to build, testing and deploying containerized application in automated manner. ### Will data on the container be lost when the docker container exits? **Data Persistence** Data within the container is lost unless you use volume or bind-mount to persist data in the container. ### What is a Docker swarm? **Docker Swarm** A container orchestration platform for managing and scaling Docker services across a cluster of machines. ### What are the docker commands for the following **Docker Commands** **1 .**`docker ps`: View running containers **2 .**`docker run -d --name `: Run a container in detached mode with a specific name **3 .**`docker export `: Export a container's filesystem **4 .**`docker load -i `: Import an existing Docker image **5 .**`docker stop `: Stop a running container **6 .**`docker rm $(docker ps -a -q -f status=exited)`: Remove all stopped containers **7 .**`docker system prune -a`: Remove unused networks, build caches, and dangling images. # **What are the common Docker practices to reduce the size of Docker images?** * Choose minimal base image. * Optimize the Dockerfile by minimizing the number of layers and combining multiple commands into single RUN instruction. * Regularly cleanup the unnecessary files and directories using .dockerignore # How do you troubleshoot a Docker container that is not starting? * Inspect Container Logs ```plaintext docker logs [container_id] ``` * Check Container Status ```plaintext docker ps -a ``` * Inspect Container Configuration ```plaintext docker inspect [container_id] ``` * Try Restarting Docker Service ```plaintext sudo systemctl restart docker ```