Ksystems Devops - Docker

Front 1

What's Docker

Back 1

Docker is a set of platform as a service products that use OS-level virtualization to deliver software in packages called containers. Containers are isolated from one another and bundle their own software, libraries, and configuration files; they can communicate with each other through well-defined channels

Front 2

What's the difference from Docker and Virtual Machine

Back 2

VM is piece of software that allows you to install other software inside of it so you basically control it virtually as opposed to installing the software directly on the computer. While a container is a software that allows different functionalities of an application independently.

Front 3

How to build an image?

Back 3

docker build -t myimage:1.0 .

Front 4

How to run a container in docker ?

Back 4

docker container run --name web

Front 5

How to pull the logs from a container?

Back 5

docker logs --tail 100 web

(Print the last 100lines of a container’s logs)

Front 6

How to list running containers

Back 6

docker container ls

Front 7

How to list all the images in docker

Back 7

docker image ls

Front 8

What's Docker Hub

Back 8

Docker's public repository for images

Front 9

What's the difference between docker and docker-compose?

Back 9

Docker commands are focused on only one container (or image) at once while docker-compose manage several containers docker.

Front 10

What's the difference between CMD, RUN, EntryPoint?

Back 10

RUN always creates a new intermediate image layer on top of the previous ones.
CMD command is used to set a default command that gets executed once you run the Docker Container. In case you provide a command with the Docker run command, the CMD arguments get ignored from the dockerfile. In the case of multiple CMD commands, only the last one gets executed.
ENTRYPOINT command, unlike CMD, does not ignore additional parameters that you specify in your Docker run command.

Front 11

What's the difference between ADD, COPY ?

Back 11

ADD - can copy from a directory or from a URL, it can copy a compressed files and automatically extract them.
COPY - cannot copy from URL. It copies just as-is

Front 12

What's EXPOSE ?

Back 12

EXPOSE instruction informs Docker that the container listens on the specified network ports at runtime. It doesn't publish the port.
To publish a port use "docker run -p 80:80"

Front 13

How to optimize Docker image size ?

Back 13

2) Base image as small as possible (alpine, busybox)

2) --no-install-recommends on install commands

3) clean-apt and remove temporary files
4) all commands in single RUN

5) use multistage dockerfiles, in stage1 to use full SDK, in stage2 use artifact from stage2 with runtime only

Front 14

Rootless controller

Back 14

Containers that can be created, run, and managed by users without admin rights.

Front 15

Command to build an image

Back 15

docker build -t <name>:<tag>

Front 16

Command to list all images

Back 16

docker images

Front 17

Command to remove image

Back 17

docker image rm <name>

Front 18

Command to pull an image

Back 18

docker pull <name>:<tag>

Front 19

Command to push and image to the registry (repo)

Back 19

docker push <name>:<tag>

Front 20

Command to run a container

Back 20

docker run <name>

Front 21

Command to stop a container

Back 21

docker stop <name>

Front 22

Command to kill a container

Back 22

docker kill <name>

Front 23

Command list the networks

Back 23

docker network ls

Front 24

Command to list all running containers

Back 24

docker ls

docker ps

to list even stopped containers add -a

docker ls -a

docker ps -a

Front 25

Command to print last 100 lines of container's logs

Back 25

docker logs --tail 100 <name>

Front 26

Command to ssh into container

Back 26

docker exec –it <name> /bin/bash

Front 27

Command to run a command in the containers

Back 27

docker exec -it <command>

docker exec -it echo "I'm inside the container!"

docker exec -it pwd

docker exec -it ls -l