DOCKER Interview Questions and Answers- Part 2

In today’s fast-moving software world, speed and consistency are everything. Docker has become a trusted solution for developers aiming to simplify application deployment. By packaging apps and their dependencies into containers, Docker eliminates the classic “it works on my machine” problem.  

Whether you’re managing microservices or scaling cloud-native apps, Docker provides the tools to deliver software faster and more reliably. 

This guide contains popular Docker interview questions and answers to help both freshers and professionals. With its help, you can do solid preparation, which will boost your confidence before interviews.  

Answer:

Docker containers are the basic software units that hold code & all its dependencies to make an application run smoothly, securely, & quickly from a computing ecosystem to another. You can use a Docker image to create a Docker Container. It is an executable software package, which covers everything required to run an application like libraries, system tools, runtime, code, and settings.

Answer:

Docker Architecture includes a Docker Engine, a client-server application having three major components:

  • A server is a type of long-running program known as a daemon process or Docker command.
  • A REST API denotes interfaces that programs can utilize to talk to the daemon & instructs what to do.
  • A CLI or command-line interface client (the docker command);
  • CLI deploys the Docker REST API to interact & control with the Docker daemon by scripting or through CLI commands. Many other Docker applications utilize the underlying CLI & API.

Answer:

A Dockerfile refers to a set of specific instructions one needs to pass onto the Docker so images can be built. It is a text document containing all the commands needed for creating an image.

Answer:

Docker Compose is a tool for running & defining multi-container apps together into an isolated environment. Either JSON or YAML file can configure the required services such as Messaging Queue, Database, & application server. Theron, you can create & start all the services from the configuration file with a single command. It comes in handy to reproduce a complete application with its services in various environments like testing, development, staging, & CI.

Answer:

A Docker container has the following lifecycle:

  • Create & Run the container;
  • Pause & Un-pause the container(optional);
  • Start the container;
  • Stop the container;
  • Restart the container;
  • Kill the container, &;
  • Destroy the container

Answer:

A Docker Machine is a tool to install virtual hosts or Docker Engine. The hosts can be managed with the docker-machine commands. Docker Machine also helps you provision the Docker Swarm Clusters.

Answer:

Docker Container is simple & easy to deploy in any of the cloud platforms. It can run multiple applications on the same hardware, unlike other technologies; it streamlines the development process & provides ready-to-run containerized applications. It also makes app deployment & management a lot easier. It enables you to even share containers with your applications.

Answer:

Docker runs on many Linux Administration:

  • Fedora 19/20+
  • RHEL 6.5+
  • CentOS 6+
  • Gentoo
  • ArchLinux
  • openSUSE 12.3+
  • CRUX 3.0+
  • Ubuntu 12.04, 13.04 et al

Docker also runs on cloud platforms:

  • Amazon EC2
  • Amazon ECS
  • Google Compute Engine
  • Microsoft Azure
  • Rackspace

() The Linux platforms are:

  • ArchLinux
  • CentOS 6+
  • CRUX 3.0+
  • Fedora 19/20+
  • Gentoo
  • openSUSE 12.3+
  • RHEL 6.5+
  • Ubuntu 12.04, 13.04 et al

Docker can also run on the following cloud-based platforms:

  • Amazon EC2
  • Amazon ECS
  • Google Compute Engine
  • Microsoft Azure
  • Rackspace

Answer:

Docker container is growing rapidly, but at the same time, Cloud Computing is giving it a tough fight. Cloud can never replace Docker, though using Cloud with Containerization will hype the game. Companies need to make a decision based on their requirements & dependencies. Most businesses will need to integrated Docker with the Cloud. This way, they can deploy both the technologies in the best manner.

Answer:

Docker doesn’t put any limitations or restrictions, so there can be as many containers as you want per host. However, you need to consider each container needs memory, storage space, CPU that the hardware needs to support. You may also consider the application’s size.

Answer:

The following are the components of Docker Architecture:

  • Host: It holds images, containers, & Docker Daemon. The Docker Daemon establishes a link with the Registry & the Docker Images act as metadata for applications held in the Docker Containers.
  • Client: The Docker Client runs operations to set up communication with the host.
  • Registry: It is used to store Docker images. Docker Cloud & Docker Hub are the public registries.

Answer:

Here are a few Docker commands:

  • Build: this command helps to build a Docker image file.
  • Create: It creates a new container.
  • Kill: It helps to kill a container.
  • Dockerd: this command is used for launching a Docker daemon.
  • Commit: it is useful for creating a new image from the container changes.

Answer:

  • Docker simplifies configuration & provides ease of configuration at the infrastructure level.
  • It increases productivity & reduces development time by helping developers concentrate on the core business logic.
  • Docker amplifies debugging capabilities.
  • It enables isolation of applications
  • Docker minimizes the use of multiple servers in containerization.
  • It facilitates rapid deployment at the Operating System level.

Answer:

For a Docker container, Stateless applications are more preferred over Stateful applications. You can create a container from your application & take out the application’s configurable state parameters. Once done, you can run the same container with other environments & different production parameters. You can reuse the same Docker image in distinct scenarios with Stateless application. Besides, when it comes to Docker Container, it is easier to scale the Stateless application than a Stateful application.

Answer:

There are mainly five default networks:

  • Bridge: It is a private default internal network created by the Docker on the host. All containers receive an internal IP address and can access each other using this internal IP. Bridge networks are used when an application run in standalone containers needs to communicate.
  • Host: It removes the network isolation between docker containers & the docker host to directly use the host’s networking. Thus, you cannot run multiple web containers on the same port & host as the port is uncommon to all containers in the host network.
  • None: All containers are not attached to a network and don’t have any access to the other containers or external network. The None network is used when you strive to completely disable the networking stack on a container & create a loopback device only.
  • Overlay: This network creates an internal private network that spans amongst all the nodes participating in the swarm cluster. It facilitates communication between a standalone container & a swarm service or two standalone containers on different Docker Daemons.
  • Macvlan: It enables you to assign a MAC address to the container, making it appear as the physical device on your network. The Docker daemon routes traffic to containers through their MAC addresses. Macvlan is the best choice when you want to directly connect to the physical network than routed through a Docker host’s network stack.

Answer:

Docker is one of the latest & new projects. Since its inception in the Cloud era, Docker has proved to be way better than other container technologies. An active community is thriving to upgrade Docker. Recently, it is extending its support to Mac OSX & Windows environments. The following are the best reasons to highlight why Docker is a better option from the existing container technologies.

  • Docker can run on any infrastructure from your laptop to a company’s Public / Private cloud space.
  • With its container hub, Docker forms the repository you need to use, work, & download. The container also allows you to share applications.
  • Docker is the best-documented technology available in the Containerization space.

Answer:

When you exit a Docker Container, you will not lose any data as all the data is written to a disk by an application for the main objective of preservation. This process is consistently repeated till the container is explicitly deleted. Besides, the file system for a Docker container persists even after the Docker container is halted.

Answer:

There are many tools available such as Docker stats & Docker events, to monitor Docker in production. Through such tools, one can get reports on essential statistics. Once the Docker statistics are called with a container ID, it returns the memory usage & the container’s CPU. It is just like the top command in Linux. Docker Events are commands to see a list of activities in process in Docker Daemon. One also gets an option to filter the events they are interested in.

Answer:

‘Docker creates’ builds a writeable container from the image & prepares it for running. ‘Docker run’ creates the container same as Docker create & runs it.

Answer:

The Docker Registry is a service for distributing & hosting images, while the Docker Hub is a default registry. However, the Docker Repository refers to a collection of Docker images that are related. They do have the same name but different tags.