What is Docker?
Since its a Docker interview, there will be an obvious question about what is Docker. Start with a small definition. Docker is a containerization platform that programs your utility and all its dependencies collectively in the structure of containers so as to make certain that your software works seamlessly in any environment, be it development, take a look at or production. Docker containers, wrap a piece of software program in a whole filesystem that incorporates the entirety wanted to run: code, runtime, device tools, gadget libraries, etc. It wraps essentially whatever that can be established on a server. This ensures that the software program will constantly run the same, regardless of its environment.
What are the advantages of using Docker container?
Here, are a main gain of the use of Docker.
• Offers an environment friendly and convenient preliminary set up
• Allows you to describe your utility lifecycle in detail
• Simple configuration and interacts with Docker Compose.
• Documentation gives each bit of information.
What are the important features of Docker?
- Easy Modeling
- Version control
- Placement/Affinity
- Application Agility
- Developer Productivity
- Operational Efficiencies
What are the main drawbacks of Docker?
- Doesn’t provide a storage option
- Offer a poor monitoring option.
- No automatic rescheduling of inactive Nodes
- Complicated automatic horizontal scaling set up
Question: Explain Docker Container?
A container is the fundamental unit of software program that holds the code and all its dependencies, in order to make the utility run smoothly, shortly and reliably from one computing ecosystem to another. A Docker container may additionally be created the usage of a Docker image. It is an executable package deal of the software, which holds the whole lot that is required to run an application, which are machine tools, libraries, code, runtime, and settings.
Explain the components of Docker Architecture?
The components in Docker architecture are given below:
- Host: This component holds the Docker Daemon, Images, and Containers. While the Docker Daemon establishes a link with the Registry, the Docker Images act as metadata for the applications which are held in the Docker Containers.
- Client: The Docker Client component runs operations to set up communication with the Docker Host.
- Registry: This Docker Component is used to store the Docker Images. Docker Hub and Docker Cloud are public registries, which can be utilized by anyone.
What is the Docker image?
The Docker image assists to create Docker containers. You can create the Docker image with the build command. Due to this, it creates a container that begins when it starts to run. Every docker images are saved in the Docker registry.
What is Docker Engine?
Docker daemon or Docker engine represents the server. The docker daemon and the clients should be run on the same or remote host, which can communicate through command-line client binary and full RESTful API.
What is Docker Hub?
Docker pictures create docker containers. There has to be a registry the region these docker pictures live. This registry is Docker Hub. Users can pick up photos from Docker Hub and use them to create customized pictures and containers. Currently, the Docker Hub is the world’s best public repository of photo containers.
Explain Docker Architecture?
Docker Architecture consists of a Docker Engine which is a client-server utility with three fundamental components:
1. A server which is a kind of long-running software referred to as a daemon system (the docker command).
2. A REST API that specifies interfaces that applications can use to speak to the daemon and teach it what to do.
3. A command-line interface (CLI) purchaser (the docker command). 4. The CLI uses the Docker REST API to control or interact with the Docker daemon through scripting or direct CLI commands. Many other Docker applications use the underlying API and CLI.
Explain the Docker Registry in detail.
The area where all Docker Images are saved is acknowledged as the Docker Registry. The Docker Hub is a public registry which is the default storage for these images. Another public registry is Docker Cloud. The Docker Hub is the most sizeable public storehouse of the picture containers, persistently maintained by using a giant wide variety of developers, alongside with many person contributors.
Name some important Docker commands
Below are some important Docker commands:
- build: to build an image file for Docker
- create: for creation of a new container
- kill: to kill a container
- dockerd: for launching Docker daemon
- commit: for creating a new image from the container changes
What are Namespaces in Docker.
Docker Namespaces is a technology imparting remoted workspaces is aware of as a container. Once a container is started, a set of namespaces is created for the stated container. These namespaces grant a layer of seclusion for these containers as every container features in a wonderful namespace, with its get right of entry to restrained to the referred to a namespace.
What is Docker Swarm?
You are predicted to have worked with Docker Swarm as it’s a necessary thought of Docker. Docker Swarm is native clustering for Docker. It turns a pool of Docker hosts into a single, digital Docker host. Docker Swarm serves the trendy Docker API, any device that already communicates with a Docker daemon can use Swarm to transparently scale to a couple of hosts.
How to identify the status of a Docker Container?
To identify the status of a Docker container, one should run the command
“docker ps-a”
This command will furnish the list of all available Docker containers with the respective status on the host. From the list one can easily make out the intended container to check its status.
What are the Docker Image and Docker Run Command?
A Docker Image is a team of documents and an amalgamation of parameters which enable the advent of situations that run in wonderful containers as remoted processes. An image is essentially constructed the usage of the guidelines for a entire and executable version of an application, which depends on the host OS kernel. The Docker run command can be used to create the instance known as container which can be run the use of the Docker image. When the Docker person runs an image, it turns into one or more than one situations of that container.
State the functionalities and applications of Docker.
Below are some functionalities and applications of implementing Docker:
- It makes the configuration simpler and provides ease of configuration at the infrastructure level
- By helping the developer concentrate exclusively on business logic, it reduces development time and increases productivity
- It amplifies the debugging capabilities which provide useful functionalities
- It allows the isolation of the application
- It reduces the use of multiple servers in the form of containerization
- It facilitates rapid deployment at the OS level
Which is more suitable for Docker Container, Stateless or Stateful application?
Stateless functions have to be favored over a Stateful software for Docker Container. For instance, we can create one container from our software and take out the configurable kingdom parameters from the app. Once it is one, we can run the identical container with one of a kind parameters in manufacturing and different environments. Through the Stateless application, we can reuse the identical image in wonderful scenarios. Also, it is less difficult to scale a Stateless application that a Stateful utility when it comes to Docker Containers.
Explain the use of Dockerfile.
Dockerfile contains a bunch of instructions that are passed on Docker to make possible the build process of images, which can automatically read these instructions. It can also be termed as a text document containing all the possible commands that a user may call on the command line for assembly of an image.
Explain how Docker is different from other container technologies.
Docker is one of the state-of-the-art container applied sciences and has emerged as one of the most popular. Built-in the technology of cloud, Docker comes with a entire lot of new aspects that had been lacking in older container technologies. One of the greatest aspects of Docker is that it can run on any infrastructure, be it your domestic desktop or the Cloud.
Through Docker, greater functions can now run on the old servers, and it additionally approves the manner to bundle and ship programs. Docker additionally has a Container Hub that acts as a repository for containers, which are effortless to down load and use. Moreover, these containers can additionally be shared through your applications. It is additionally very well documented, which makes it higher than different container technologies.
Will you lose your data, when a docker container exists?
No, you won’t lose any data when Docker container exits. Any data that your application writes to the container gets preserved on the disk until you explicitly delete the container. The file system for the container persists even after the container halts.
Where all do you think Docker is being used?
When requested such a question, reply by way of speaking about the purposes of Docker. Docker is being used in the following areas:
• Simplifying configuration: Docker lets you put your surroundings and configuration into code and set up it.
• Code Pipeline Management: There are specific structures used for improvement and production. As the code travels from development to checking out to production, it goes thru a distinction in the environment. Docker helps in keeping the code pipeline consistency.
• Developer Productivity: Using Docker for improvement offers us two matters – We’re nearer to manufacturing and improvement environment is constructed faster.
• Application Isolation: As containers are purposes wrapped collectively with all dependencies, your apps are isolated. They can work via themselves on any hardware that helps Docker.
• Debugging Capabilities: Docker helps more than a few debugging types of equipment that are now not unique to containers however work properly with containers.
• Multi-tenancy: Docker lets you have multi-tenant purposes averting redundancy in your codes and deployments.
• Rapid Deployment: Docker eliminates the want to increase an complete OS from scratch, decreasing the deployment time.
What is the difference between a registry and a repository?
The Docker Registry is a service for hosting and distributing images, whereas the Docker Hub is the default registry. On the other hand, the Docker Repository is the collection of Docker images that are related. That is, they have the same name but different tags.
Shed some light on the workflow of Docker usage.
Below is a short rationalization of the workflow of Docker usage:
• Since the Dockerfile is the source code of the image, the entirety begins with it.
• Once it is created, the Dockerfile is used to construct the photograph of the container. This image is solely the compiled model of the Dockerfile.
• This picture has then redistributed the use of the registry, which is like a repository of images.
• Further, the picture can be used to run containers. A container, whilst it is running, is very comparable to a VM besides the hypervisor.
Explain the disparity between the commands ‘Docker run’ and ‘Docker create’.
The primary difference between Docker run and Docker create is that if you use the latter, the container is created in a ‘stopped’ state. Also, Docker creates can be used to store and output container ID for use at a later time. The best way to do it is to use ‘docker run’ with —cidfile FILE_NAME as running it again won’t allow overwriting the file.
What platforms does docker run on?
This is a very straightforward question but can get tricky. Do some company research before going for the interview and find out how the company is using Docker. Make sure you mention the platform company is using in this answer.
Docker runs on various Linux administration:
- Ubuntu 12.04, 13.04 et al
- Fedora 19/20+
- RHEL 6.5+
- CentOS 6+
- Gentoo
- ArchLinux
- openSUSE 12.3+
- CRUX 3.0+
It can also be used in production with Cloud platforms with the following services:
- Amazon EC2
- Amazon ECS
- Google Compute Engine
- Microsoft Azure
- Rackspace
Is it a good practice to run Docker compose in production?
Yes, the use of docker compose in manufacturing is the fine realistic software of docker compose. When you outline functions with compose, you can use this compose definition in a number of production ranges like CI, staging, testing, etc.
What changes are expected in your docker compose file while moving it to production?
These are the following modifications you want make to your compose file earlier than migrating your software to the manufacturing environment:
• Remove extent bindings, so the code stays interior the container and can’t be modified from backyard the container.
• Binding to extraordinary ports on the host.
•Specifyarestartpolicy
• Add greater offerings like log aggregator