1 . What is the difference between an Image, Container and Engine?
1(i). Docker Image:
The concept of Image and Container is like class and object, in which an object is an instance of a class, and a class is the blueprint of the object. Images are different in Virtual Machines and dockers.
- In virtual machines, images are just snapshots of running virtual machines at different points in time, but Docker images are a little bit different.
- The most important and major difference is that Docker images are immutable. That is they can not be changed. In the real world, it happens a lot that software works on one computer but it does not work on others due to different environments.
- This issue is completely solved by docker images and using this, the application will work the same on everyone’s PC.
-Every developer on a team will have the same development instance.
-Each testing instance is the same as the development instance. Your production instance is the same as the testing instance.
-1(ii). Container:
-They are Docker Virtual Machines but are commonly called Docker Containers.
-If a Docker image is a map of the house, then a Docker container is a built house, or in other words, we can call it an instance of an image.
-As per the official website, a container is a runnable instance of an image.
-You can create, start, stop, move, or delete a container using Docker API or CLI.
-You can connect a container to one or more networks, attach storage to it, or even create a new image based on its current state.
-An application runs using a cluster of containers that are self-isolated from one another and also from the host machine where they are running.
-1(iii). Docker Engine
-is an open-source containerization technology for building and containerizing your applications.
-Docker Engine acts as a client-server application with A server with a long-running daemon process docked.
-APIs that specify interfaces that programs can use to talk to and instruct the Docker daemon.
-Docker Engine is the core product of Docker, including its daemon (docked) as well as its CLI (docker). -
Docker Daemon is simply a part of the Docker Engine
What is the Difference between the Docker command COPY vs ADD?
-COPY and ADD are both Dockerfile instructions that serve similar purposes. They let you copy files from a specific location into a Docker image.
-COPY takes in an src and destination. It only lets you copy a local file or directory from your host (the machine building the Docker image) into the Docker image itself.
-ADD lets you do that too, but it also supports 2 other sources. First, you can use a URL instead of a local file/directory.
-Secondly, you can extract a tar file from the source directly into the destination
-The ADD instruction can do things more than just copying the directories or files from the localhost.
-We can use the ADD instruction to pull the files or directories from external links/URLs such as Github, Bitbucket, etc.
-The ADD instruction can also be used to extract compressed files such as archives or tarball files.
-However, sometimes, it might cause a problem if you don’t want to extract the archives
What is the Difference between the Docker command CMD vs RUN?
-RUN is an image build step, the state of the container after a RUN command will be committed to the container image.
-A Dockerfile can have many RUN steps that layer on top of one another to build the image.
-CMD is the command the container executes by default when you launch the built image.
How Will you reduce the size of the Docker image?
-Using distress/minimal base images.
-Multistage builds.
-Minimizing the number of layers.
-Understanding caching.
-Using Dockerignore.
-Keeping application data elsewhere.
Why and when to use Docker?
-You can use Docker to wrap up an application in such a way that its deployment and runtime issues, how to expose it on a network, how to manage its use of storage and memory and I/O, how to control access permissions—are handled outside of the application itself, and in a way that is consistent across all “containerized
Explain the Docker components and how they interact with each other.
-Docker works via a Docker engine that is composed of two key elements: a server and a client; and the communication between the two is via REST API.
-The server communicates the instructions to the client.
Explain the terminology: Docker Compose, Docker File, Docker Image, Docker Container?
-Docker Compose is a tool that was developed to help define and share multi-container applications. With Compose, we can create a YAML file to define the services and with a single command, can spin everything up or tear it all down.
-A Dockerfile is a text document that contains all the commands a user could call on the command line to assemble an image. This page describes the commands you can use in a Dockerfile.
-A Docker image is a read-only template that contains a set of instructions for creating a container that can run on the Docker platform.
-A Docker container image is a lightweight, standalone, executable package of software that includes everything needed to run an application: code, runtime, system tools, system libraries and settings.
In what real scenarios have you used Docker?
-Docker allows you to provision fewer resources enabling you to run more apps and facilitating efficient optimization of resources.
For example, developer teams can consolidate resources onto a single server thus reducing storage costs.
Docker vs Hypervisor?
-Hypervisors can be made to work on software and hardware where it works on the operating system or the CPU and storage services of the system.
-More power and resources are required by the systems using hypervisors as different programs are being run on the same system with different operating systems
-Dockers work only on the software of the operating system and not on the hardware side.
It takes the host kernel and works on the principle of virtualization.
-Resource requirement is low as containers are working on the same operating system and this makes the system share resources within the containers
What are the advantages and disadvantages of using docker?
-#BENEFIT OF DOCKER
-Docker produces an API for container management
-fast application.
-transferable across machines
-version control
-sharing
-light and minimal
-#DISADVANTAGES
-Containers don’t work at bare
-metal rates
-Data storage is intricate (FOREVER)
-Graphical applications do not operate well
-Few applications do not benefit from Docker Containers
What is a Docker namespace?
-Docker uses a technology called namespaces to provide the isolated workspace called the container.
--When you run a container, Docker creates a set of namespaces for that container. -These namespaces provide a layer of isolation.
What is a Docker registry?
-A registry is a storage and content delivery system, holding named Docker images, available in different tagged versions.
-Example: the image distribution/registry, with tags 2.0 and 2.1. Users interact with a registry by using docker push and pull commands.
What is an entry point?
-ENTRYPOINT is one of the many instructions you can write in a docker file. The ENTRYPOINT instruction is used to configure the executables that will always run after the container is initiated. For example, you can mention a script to run as soon as the container is started.
How to implement CI/CD in Docker?
-Step one: Create the repository
-Step two: Set up the workflow
-Step three: Define the workflow steps
Will data on the container be lost when the docker container exits?
-Not at all! Any data that your application writes to disk gets preserved in its container until you explicitly delete the container.
What is a Docker swarm?
-A Docker Swarm is a container orchestration tool running the Docker application. It has been configured to join together in a cluster.
-A swarm is a cluster of one or more computers running Docker. It can consist of one or more machines, so you can use swarm functionality on your local machine
What are the docker commands for the following:
---------view running containers
-docker ps” or “docker container ls”
---------command to run the container under a specific name
-docker exec --workdir /tmp container-name pwd.
---------command to export a docker
-docker export
---------command to import an already existing docker image
-docker import
---------commands to delete a container
-docker stop <Container_ID> -docker rm <Container_ID>
---------command to remove all stopped containers, unused networks, build caches, and dangling images?
-docker system prune
What are the common Docker practices to reduce the size of Docker Images?
-Bundling layers. The size of a Docker image is the sum of its layers. -Avoid installation of unnecessary packages. -Clean up after installation. -How about a smaller image?