Containerization

Question 1

What is the purpose of containers?

Answer 1

• Isolate software from its surroundings, for example differences between development and staging environments.
• Help reduce conflicts between teams running different software on the same infrastructure.

Question 2

How to configure a Docker container?

Answer 2

• Create a docker-compose.yml file at the root of a project.
• This YAML file defines how containers should behave in production.
• It should specifies the compose file format (or version), the services, networks and volumes.

Question 3

Start a docker container.

Answer 3

$ docker-compose up

Shorthand for $ docker-compose build && docker-compose run

Question 4

How to run docker commands without putting a sudo in front of them?

Answer 4

Add username to docker group.

Question 5

What is containerization?

Answer 5

The process of distributing and deploying apps in a portable and predictable way. It accomplishes this by packaging components and their dependencies into standardized, isolated, lightweight process environments called containers.

Question 6

Describe the docker compose workflow.

Answer 6

1. Define each service in a dockerfile.
2. Define the services and their relation to each other in the docker-compose.yml file.
3. Use docker-compose up to start the system.

Question 7

List the running docker containers.

Answer 7

$ docker-compose ps

Question 8

What are the main functions of docker compose?

Answer 8

• Main: creation of microservice architecture (i.e. containers and the links between them).
• Building images (if an appropriate dockerfile is provided).
• Scaling containers running a given service.
• Healing: re-running containers that have stopped.

Question 9

What is a container?

Answer 9

A container image is a lightweight, stand-alone, executable package of a piece of software that includes everything needed to run it: code, runtime, system tools, system libraries, settings.

Question 10

Differences between containers and VMs.

Answer 10

Containers:

• Abstraction of the app layer that packages code and dependencies together.
• Multiple containers can run on the same machine, sharing the OS kernel and running as isloated processes.
• Containers take up less space than VMs (~10 MBs) and start almost instantly.

VMs:

• Abstraction of physical hardware turning one server into many.
• Hypervisor allows multiple VMs to run on a signle machine.
• Each VM includes a full copy of an OS, apps, binaries and libraries.
• VMs takes more space (~10 GBs) and are slow to boot.

Question 11

What is a dockerfile?

Answer 11

A dockerfile is a text document that contains all the commands a user could call on the command line to assemble an image.

Question 12

List local docker images and inspect them.

Answer 12

$ docker image ls

$ docker inspect [id]

Question 13

Run services in the background with docker.

Answer 13

$ docker-compose up -d

Explanation of -d: “detached mode”

Question 14

Run one-off commands for services with docker-compose.

Answer 14

$ docker-compose run [service] [command]

Question 15

Stop services with docker-compose.

Answer 15

$ docker-compose stop

Question 16

Stop and remove containers, default network and networks defined in the network section of the compose file with docker-compose. Optional: remove images and volumes.

Answer 16

$ docker-compose down

$ docker-compose down –rmi (local/all) –v