Part 5: Docker Interview Questions And Answers

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To be uploaded soon..

-K Himaanshu Shuklaa..

Part 4: Docker Interview Questions And Answers (Docker Swarm)

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Explain Docker Swarm.
Docker engine is hosted on a particular host, with Docker Swarm we can start the same host on multiple machines. There will be a master machine(which is docker manager) and then we have different slaves/workers. Whatever service we start on manager, will be started on slaves.

Swarm command creates a network of Docker engines/ hosts to execute containers in parallel (for scaling up and high availability).

A Docker Swarm is a service that allows us to create and manage a cluster of Docker nodes and schedule containers. Each node of a Docker Swarm is a Docker daemon, and all Docker daemons interact using the Docker API. Each container within the Swarm can be deployed and accessed by nodes of the same cluster.

What are the features of Docker Swarm?

• Decentralized Access: Swarm makes it very easy for teams to access and manage the environment 
• High Security: Any communication between the manager and client nodes within the Swarm is highly secure 
• Auto Load Balancing: There is autoload balancing within your environment, and you can script that into how you write out and structure the Swarm environment 
• High Scalability: Load balancing converts the Swarm environment into a highly scalable infrastructure
• Roll-back A Task: Swarm allows you to roll back environments to previous safe environments.

How does Docker Swarm work?
In Swarm, containers are launched using services, where a service is a group of containers of the same image that enables the scaling of applications. Before we can deploy a service in Docker Swarm, we must have at least one node deployed.

There are two types of nodes in Docker Swarm:

• Manager node: This node maintains cluster management tasks.
• Worker Node: It receives and executes tasks from the manager node.

The manager node knows the status of the worker nodes in a cluster, and the worker nodes accept tasks sent from the manager node. Every worker node has an agent that reports on the state of the node's tasks to the manager.

The worker nodes communicate with the manager node using API over HTTP. In Docker Swarm, services can be deployed and accessed by any node of the same cluster. While creating a service, you'll have to specify which container image you're going to use.

You can set up commands and services to be either global or replicated: a global service will run on every Swarm node, and on a replicated service, the manager node distributes tasks to worker nodes. 

Getting started with Swarm Mode
Manager intiate the Docker Swarm. Here the manager is the instance which starts the Swarm cluster. The command to start the cluster is:

$ docker swarm init --advertise-addr < ip-address >

Here, the '--advertise-addr’ flag is used for advertising itself to other nodes who want to join the cluster. We need to specify the IP address of the manager along with the flag.

When the Swarm cluster is initiated, a token is generated at the manager’s end. Other nodes use this token to join the swarm cluster.

Any node that joins the cluster can be later promoted to a manager, to do this we need to execute below command at the manager’s end:

$ docker swarm < join-token > manager

Later when we want the token for a node to join the cluster, we need to run the below command:

$ docker swarm < join-token > node

We need to execute the token at every node you want, to join the cluster.

To leave the swarm, use

$ docker swarm leave

OR to leave force-ably

$ docker swarm leave --force

-K Himaanshu Shuklaa..

Part 3: Docker Interview Questions And Answers (docker-compose command)

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How to use the docker-compose command?
Docker Compose is used to run multiple containers as a single service.

This command is used to power multi-container applications where various services will be hosted inside different containers.

Part 2: Docker Interview Questions And Answers (Docker Commands)

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How to check for Docker Client and Docker Server version?
$ docker --version

Can a container restart on its own?
Since the default flag -reset is set to false, a container cannot restart by itself.

Part 1: Docker Interview Questions And Answers

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What is Virtualization?
Virtualization is the process of creating a software-based, virtual version. These virtual versions or environments are created from a single physical hardware system.

With the help of Virtualization we can split one system into many different sections which act like separate, distinct individual systems.

What is Hypervisor?
A hypervisor also called Virtual Machine Monitor is a software that makes virtualization possible. The virtual environment created by the hypervisor is called Virtual Machine.

It divides the host system and allocates the resources to each divided virtual environment. We can  have multiple OS on a single host system. There are two types of Hypervisors:

• Type 1: It’s also called Native Hypervisor or Bare metal Hypervisor. It runs directly on the underlying host system. It has direct access to your host’s system hardware and hence does not require a base server operating system.
• Type 2: It is also known as Hosted Hypervisor and this kind of hypervisor makes use of the underlying host operating system.