Exercise 2 PDF Information

Question 1

Problems with Mongo DB deployment?

Answer 1

• OS dependent. Different deployment procedure and requirements for different OS
• not scalable: run on more laptops or VMs? not an ideal solution
• not portable: running the same procedure from scratch on a new machine is a waste of time

-> Solution: containerization

Question 2

What is containerization?

Answer 2

• An OS-level virtualisation method for deploying and running distributed applications without launching an entire VM for each application.
• Share the same OS kernel as the host

Question 3

What is the docker engine composed of?

Answer 3

Docker Daemon (executes commands of Docker client)
Docker Client (communicates with the Docker Daemon)
REST API (for interaction with Docker Daemon remotely)

Question 4

What is the docker daemon? Where does it gets its information from?

Answer 4

The docker client talks to the docker daemon, which does the heavy lifting of building, running, and distributing docker containers.

Question 5

What does the Docker provide unified access to?

Answer 5

• linux container technology (cgroups, namespaces)
• various container implementations

Question 6

What is a runtime (internet)

Answer 6

A runtime, in the context of containerization, is the software that is responsible for creating and managing the execution of containers. It provides the low-level functionality necessary to start, stop, and manage the container’s process, such as creating namespaces, cgroups, and network interfaces

Question 7

docker container process (low-level)

Answer 7

Question 8

Dockerfile

Answer 8

A Dockerfile is a script that contains a set of instructions that are used to build a Docker image. It is a plain text file that contains all the commands, in order, needed to build a specific version of an image.

Question 9

Docker registry (internet)

Answer 9

A Docker registry is a service that stores and distributes Docker images. It is a central location where developers can upload and share their images, and from where users can download and run those images on their own systems.

Question 10

Advantage of containers

Answer 10

• packs your application in a container with all of your applications bins/libs and dependencies
• makes it fully isolated from external environments regardless of where it is running
• we can ship that container to anywhere (any other OS, to Docker Registry)

-> OS independent, scalable, portable

Question 11

How does an image relate to layers?

Answer 11

• a docker image is built up from a series of layers
• each layer represents an instruction of the image’s Dockerfile
• a new writable layer on top of the underlying layers often called “container layer” and is added when a new container is created

Question 12

Difference between a container and image

Answer 12

• the major difference between a container and an image is the top writable layer
• all new writes to the container are stored in this writeable layer
• multiple containers can share access to the same underlying image and yet have their own data state

Question 13

Docker Containers build flow

Answer 13

Question 14

Explain the meaning of:
FROM node:alpine

Answer 14

FROM node:alpine is a command used in a Dockerfile, which is used to build a Docker image. This command specifies that the base image for the new image being built should be the official Node.js image with the tag “alpine”. Alpine Linux is a lightweight Linux distribution that is often used as the base image for Docker images because it is small and has a minimal set of packages installed, which makes the resulting image smaller and more secure.

Question 15

Explain the meaning of:
RUN mkdir -p /usr/src/server

Answer 15

Create a new directory named server in the /usr/src/ directory. This command is commonly used to create a directory where the application code will be stored in the container.

RUN mkdir -p /usr/src/server is a command used in a Dockerfile, which is used to build a Docker image. This command tells Docker to run the command mkdir -p /usr/src/server in the container, when the image is built.

mkdir is a command in Linux and Unix-like operating systems that creates a new directory.
-p option creates the parent directory if it doesn’t exist.
/usr/src/server is the path to the new directory that will be created.

Question 16

Docker run command

Answer 16

Question 17

Explain the meaning of:
WORKDIR /usr/src/server

Answer 17

the WORKDIR instruction sets the working directory for the container, and all the subsequent instructions like ‘RUN’ will be executed relative to this directory.

Question 18

Copy the package.json file which contains all the dependencies required for the application

Answer 18

Explain the meaning of:
COPY package.json /usr/src/server/

Question 19

This command will install all the dependencies listed in package.json

Answer 19

Explain the meaning of:
RUN npm install

Question 20

This command copies all files and directories from the build context (the directory where the Dockerfile is located) to the specified destination directory /usr/src/server inside the container file system.

Answer 20

COPY . /usr/scr/server

Question 21

Expose container port to the host machine

Answer 21

Explain the meaning of:
EXPOSE 3000

Question 22

A start command to run the application

Answer 22

Explain the meaning of:
CMD [“node”, “server.js”]

Question 23

What is the Docker HUB?

Answer 23

• cloud based registry service
• allows you to link code repositories, build your images, stores manually pushed images, and links to Docker Cloud so you can deploy images to your hosts

Question 24

What does the Docker run command do?

Answer 24

Docker –> tells the OS that you are using the docker program
run –> a subcommand that creates & runs a docker container
‘hello-world’ –> tells the docker which image to load into the container

Question 25

What are tags used for with Images?

Answer 25

A tag is a subcommand that tags an image s that different versions of the image can identified.

Question 26

Build an image from the Dockerfile in the directory and tag the image

Answer 26

Explain the meaning of: docker build -t :

Question 27

lists all images that are locally stored with the Docker engine

Answer 27

Explain the meaning of: docker images

Question 28

List running containers

Answer 28

docker ps

Question 29

stop a running container

Answer 29

Explain the meaning of: docker stop

Question 30

remove a running container

Answer 30

Explain the meaning of: docker rm

Question 31

delete an image from the local image store. The local image store is a repository where Docker images are stored on a local machine.

Answer 31

Explain the meaning of: docker rmi

Question 32

When a container exits, by default, it is not removed from the host, it remains in the stopped state. This means that the container still exists and takes up disk space. If you want to remove the container after it exits, you can use the "" option when starting the container.

Answer 32

--rm

Question 33

command to start an interactive container in a terminal. This allows you to interact with the container by typing commands and receiving output.

Answer 33

-it

Question 34

name the container

Answer 34

--name

Question 35

expose port 5000 externally and map to port 80

Answer 35

-p 5000:80

Question 36

mount a host directory ~/dev as a volume inside a container at the path /code. This allows the files and directories in the host's ~/dev to be accessed and modified by the processes running inside the container. This option is useful for sharing data between the host and container, or for persisting data when the container is deleted.

Answer 36

-v~/dev:/code

Question 37

the image from which the container is instantiated

Answer 37

image:tag

Question 38

The container will start and give you an interactive shell prompt where you can run commands inside the container.

Answer 38

/bin/sh

Question 39

What is docker-compose

Answer 39

- compose is a tool for defining and running multi-container docker applications

Question 40

docker-compose build

Answer 40

build all the images

Question 41

docker-compose build

Answer 41

build only the selected image

Question 42

docker login docker login

Answer 42

log in to a registry (the docker hub by default)

Question 43

docker-compose push

Answer 43

push images to registry

Question 44

docker-compose up

Answer 44

used to start all containers

Question 45

docker-compose up -d

Answer 45

to start all containers in the background

Question 46

docker-compose stop

Answer 46

stop the containers

Question 47

docker-compose kill

Answer 47

kill the containers