Docker Cheatsheet

Docker_Cheatsheet.md

Welcome to Docker

• We downlaod the docker image.
• Underlying host where docker is installed is called Docker Host
• when we run the image, a container is created from that image.
• that container runs.
• we can run multiple container of same images.
• every running container is assigned a container-name and container-id randomly by docker
• we don't need to type full container-id. just type the minimum chars to distiguish from other running containers.

Run

docker run ubuntu

• To run container with specific name

docker run --name koolbantu ubuntu

• run the image
• if image is not downloaded, it'll download it.

List Containers

docker ps

• List all running docker containers

docker ps -a

• List all containers, running and exited

Stop a container

docker stop <container-id/container-name>

Delete a container

docker rm <container-name>

List images

docker images

Delete images

docker rmi <image-name>

Download an image

docker pull <image-name>

• It will donwload the image but not run it.

Run a command after running container

docker run <image-name> <commands>

• Example run ubuntu and sleep for 20 sec

docker run ubuntu sleep 20

Execute commmand on running container

docker exec <container-name> <command>

• Example

docker exec cold_aryabhata cat /etc/hosts

Run container in background (detach)

docker run -d <image-name>

Bring background container in foreground

docker attach <container-name/container-id>

Run specific version of image

docker run <image-name>:<tag>

• Example

docker run mongodb:4.0

• By default, it runs the latest version

Run container in interactive mode

docker run -i <image-name>

• Now we can interect with it.
• but still terminal input is missing (Enter your name:)
• So for showing terminal output, use -t

docker run -it <image-name>

PORT mapping

• Every docker container is assigned an IP.
• It is internal IP and only accessible without the docker host
• Outside docker host, this is not accessiable.
• So we map docker host's port to container's port

docker run -p <host-PORT>:<docker-PORT> <image-name>

• Example

docker run -p 1100:5000 mywebapp

• it will map host machine port 1100 to docker port 5000
• means, request coming to host machine port 1100 will be redirected to docker image's port 5000.

Volume mapping

docker run -v <host-dir>:<docker-dir> <image-name>

• Example

docker run -v /opt/mydata:/var/lib/mysql mysql

• It will map host machine's opt/mydata folder to docker container's /var/lib/mysql folder
• Means whatever data will come to docker's /var/lib/mysql folder, will be directed to host's /opt/mydata folder.

Inspect container

docker inspect <container-name/container-id>

See container logs

docker logs <container-name/container-id>

Environment Variable- way to pass variable data to container

docker run -e HI_COLOR=blue mywebapp
docker run -e HI_COLOR=green mywebapp

• Inside the container, this env variable can be used
• For instance, for python

color= os.environ.get('HI_COLOR')

• use docker inspect <container-id|container-name> command to get env-variables of running container.

Create Docker Image

To create docker image all you need is a Dockerfile

• Create a file named Dockerfile (no extension)
• copy this content (you will learn later what is this)

FROM ubuntu

RUN apt update
RUN apt install -y python python-pip 

RUN pip install Flask 

COPY app.py /opt/app.py

ENTRYPOINT FLASK_APP=/opt/app.py flask run --host=0.0.0.0

• now, in the same dir, run this command

docker build . -t shivampip/myflask

• . means source files are in current dir
• -t means give image a tag (name)
• only myflask is also fine but in that case can't be pushed to docker hub.
• to be able to push to docker hub, use <docker-username>/<image-name>

Push image to Docker Hub

docker login
docker push shivampip/myflask

CMD

• CMD command runs plain

CMD sleep 10

or

CMD ["sleep", "10"]

ENTRYPOINT is where we can pass variable params

ENTRYPOINT ["sleep"]
CMD ["5"]

• Now while running

docker run mysleeper 20

this will be like

docker run mysleeper sleep 20

• if value not provided, default is 5

Restrict container CPU useas

docker run --cpus=.5 ubuntu

• .5 means 50% CPU

Restrict container memory useas

docker run --memory=400m ubuntu

• 400m means 400 Mb