Docker Notes - Best Practices

Table Content

1. Docker Architecture
Cheat Sheet
Docker CLI
4.1. List all docker image
4.2 Running ubuntu bash
4.3. List of containers
4.4. Docker commit
Running processes in container
5.1. View output of container
5.2. Kill a container
Manage container
6.1. Memory limits
6.2. CPU limits
Networking
7.1. Getting container ip
7.2. UDP ports
Connecting between Containers
8.1. host -> container
8.2. container --> container
container connects to other container directly.
Listing images
10.1. Getting images
10.2. Removing images
Volumes
11.1. Sharing data with the host
11.2. Sharing Data between Containers
Docker Registries
12.1. Finding Images
Dockerfile
References

1. Docker Architecture

2. Setup

• CentOS

3. Cheat Sheet

https://github.com/wsargent/docker-cheat-sheet#why-docker

4. Docker CLI

4.1. List all docker image

docker images

4.2 Running ubuntu bash

• image --> docker run --> running container --> stopped container --> docker commit --> new images
• image is not change.

-ti = terminal keyboardInteractive

docker run -ti ubuntu:latest

4.3. List of containers

docker ps

List of docker with format

docker ps --format $FORMAT

List all (-a)

docker ps -a

List last (-l)

docker ps -l

4.4. Docker commit

• create new image from container

docker commit <docker id | name> [<new-image-name>]

• set tag for new images

docker tag < sha256 > < tag-name >

ex:

docker tag 52caa40054059fc07e4148337efa0a937799dc25ddc6b2e9f4d7deec4cf63177 my-image

test:

docker run -ti my-image

5. Running processes in container

• --rm : do not keep container after finish process

docker run --rm -ti ubuntu sleep 5
docker run --rm -ti ubuntu cat /etc/hosts
docker run -ti ubuntu bash -c "sleep 5; echo done"

• -d : (detach) run docker process in background

docker run -d -ti ubuntu bash

• attach

docker ps -l [--format $FORMAT]
docker attach <container-name>

• detach, leave it running in background

Control P + Control Q

• add another process in existed container

docker exec -ti <container-name> <command>

ex:

docker exec -ti gifted_kirch bash

5.1. View output of container

docker logs <container-name>

ex:

docker run --name my-container -d ubuntu bash -c "more /etc/hosts"
docker logs my-container

5.2. Kill a container

docker kill <container-name>

6. Manage container

6.1. Memory limits

docker run --memory <maxium-allowed> <image-image> <command>

6.2. CPU limits

docker run --cpu-shares relative to other containers
docker run --cpu-quota to limit it in general

7. Networking

ex:

• echo-server ( -p portin[:portout] )

docker run --rm -ti -p 45678:45678 -p 45679:45679 --name echo-server ubuntu:14.04 bash

nc -lp 45678 | nc -lp 45679

7.1. Getting container ip

docker ps docker inspect <container-id> | grep IP

nc <container-ip> <port>

ex1:

nc 172.17.0.2 45678 nc 172.17.0.2 45679

ex2:

docker run --rm -ti -p 45678 -p 45679 --name echo-server ubuntu:14.04 bash

docker port echo-server

7.2. UDP ports

docker run -p ousite-port:insite-port/protocol(tcp/udp)

ex:

docker run -p 1234:1234/udp

8. Connecting between Containers

Client Container-->Host Network--->Virtual Network ---> Server Container

ex:

docker run -ti --rm -p 1234:1234 unbuntu:14.04 bash nc -lp 1234

8.1. host -> container

docker ps -l docker inspect <container-id> | grep IP nc <container-ip> 1234

8.2. container --> container

docker run -ti --rm ubuntu:14.04 bash nc <container-id> 1234

9. container connects to other container directly.

• server

docker run -ti --rm --name server ubuntu:14.04 bash
nc -lp 1234

• client

docker run --rm -ti --link server --name client ubuntu:14.04 bash
nc server 1234

• Link directly:
• A service with its DB - not good
• Automatically assigns a hot name
• That links can break when containers restart

9.1. Making Links Not Break

• Docker has private networks.
• Fix the Links
• Must create the networks in advance

docker network create <network-name>

ex:

• server

docker network create example
docker run --rm -ti --net=example --name server ubuntu:14.04 bash
nc
nc -lp 1234

• client

docker run --rm -ti --link server --net=example --name client ubuntu:14.04 bash
nc server 1234

• Now kill the server and restart again.
• The link between server and client does not break.

9.2. Limiting access to only host

docker run -p 127.0.0.1:1234:1234/tcp

10. Listing images

• List downloaded images

docker images

• Tagging gives images

docker commit <container-id|name> <new-image-name>[:<tag>]

ex:

docker ps -l
docker commit b5938fe91f4c my-image-now
docker images

10.1. Getting images

• for offline work

docker pull

10.2. Removing images

docker rmi <image-name|id>

ex:

docker images
docker rmi my-image

11. Volumes

• Sharing data between containers and containers and host.
• Virtual "dicsc"
• Two types:

+ Persistent : Keep when container went away. + Ephemeral: exists in container life.

• Volumes is not a part of image.

11.1. Sharing data with the host

• like VMware.
• Sharing folders with the host

ex:

mkdir /home/docker/my-volume
docker run -ti -v=/home/docker/my-volume:/shared-folder ubuntu bash
cd /shared-folder
touch my-data
Press Crtl + D
ls ./my-volume/shared-folder

• Sharing a "single file" into a container

11.2. Sharing Data between Containers

• volumes-from
• Shared disks that exist only as long as they are being used
• Can be shared between containers

ex

• Container #1

docker run -ti -v /shared-data ubuntu bash echo "hello, is it great!" > /shared-data/my-file

• Container #2

docker ps -l docker run -ti --volumnes-from jovial_goodall ubuntu bash cat /shared-data/my-file

12. Docker Registries

• Registries and distributes images.

12.1. Finding Images

https://hub.docker.com

docker search centos

• Push image to the world.

docker login
docker pull centos
docker tag centos:123 test/test-image-32:v123.1234
docker push test/test-image-32:v123.1234

Note: Do not push password with the image

13. Dockerfile

• What is it ?
• code to create image

docker build -t name-of-result .

• each line takes the image of previous line and makes another images.
• the previous image is unchanged.

14. References

• https://docs.docker.com/engine/reference/builder/
• http://apachebooster.com/kb/wp-content/uploads/2017/09/docker-architecture.png
• https://github.com/wsargent/docker-cheat-sheet#why-docker
• http://extremeautomation.io/img/cheatsheets/cheatsheetdockerpage1.png