ritik-malik/docker_cheatsheet.md

## docker_cheatsheet.md

      
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              docker_cheatsheet.md
            
          
    Docker CLI Overview & Cheatsheet

Getting Started

Downloading Docker


Head on to https://docs.docker.com/get-docker and select the appropriate OS
Since I'll be doing it on Ubuntu 20.04 - https://docs.docker.com/engine/install/ubuntu/

Now there are 3 options to install -

Install using the repository
Install from a package
Install using the convenience script


I'll be using the 3rd option, so only 3 commands here -

curl -fsSL https://get.docker.com -o get-docker.sh
chmod +x get-docker.sh
sudo sh get-docker.sh


For running docker in rootless mode, refer to this link

Testing


Check the docker version: sudo docker version
Do a simple test - head on to https://hub.docker.com/r/docker/whalesay
We'll use this image for a test run

sudo docker pull docker/whalesay Save the whales! - pull the image and run it


Next time it will run from the local image

Docker basic commands


Command
Description


docker version
to check the version of docker installed


docker run nginx
to start a container of nginx from image (if already exist, else it will pull from hub)


docker run --name myserver nginx
to start a container of nginx with a name


docker ps
list all running containers


docker ps -a
to list all containers - currently running as well stopped ones


docker stop containerID/name
to stop a running container provide either name or ID (first few letter works as long as it unique)


docker rm containerID/name
to remove a container permanently


docker rm -f containerID/name
to remove a running container permanently


docker images
to see a list of available images


docker rmi name
to delete a docker image


docker pull nginx
to only pull the docker image and not run the container


docker exec ubuntu cat /etc/passwd
to execute command in a container


docker run -d ubuntu:latest
to run and detach a container


docker attach ID/name
to attach back to the running container


docker cp nginx:file.txt data/
to copy a file from container to host [cp container:source target] (just like scp)


docker cp data.txt nginx:file.txt 
to copy a file from host to container [cp target container:source]


Docker run


Command
Description


docker run redis:4.0
to run a container with a different version, specify with name:tag format (will take latest tag by default)


docker run -i name
to run in interactive mode (by default won't take input from STDIN)


docker run -it name
to attach a psuedo terminal to the container


docker run -p 69:3306 mysql
to map the port 69 of localhost/dockerhost to port 3306 of the container running mysql (-p HOST:CONTAINER)


docker run -P mysql
to map all ports


docker run -v /opt/datadir:/var/lib/mysql
to persist the data : map a dir outside the container on docker host to a dir inside the container (-v HOST:CONTAINER)


docker inspect name/ID
to inspect a container (output JSON)


docker logs name/ID
to view logs of a container


docker stats
to view stats of running containers


docker top name/ID
to view processes of a container


Docker environment variables


Command
Description


docker run -e BG_COLOR=blue simple-webapp-color
to set the environment variable for our container


docker inspect name/ID
to find the env var in a running container, refer to config section in output


Docker Images


Command
Description


docker build Dockerfile -t webserver/release-one
to build a docker image with a Dockerfile and give it a tag


docker tag Ubuntu Ubuntu:20.04
to tag an image


docker build .
build an image from Dockerfile in current directory


docker save nginx > nginx.tar
save an image to tar file


docker load -i nginx.tar
load an image from tar file


docker push webserver/release-one
to host it on docker hub community (docker registry)


Docker CMD vs ENTRYPOINT


In case of CMD, when we pass a cmd line argument, docker run ubuntu sleep 10, it will replace the CMD in the Dockerfile
In case of ENTRYPOINT, when we pass a cmd line argument, docker run ubuntu 10, it will get appended to ENTRYPOINT in the Dockerfile
If user doesn't pass an arg, use both of them instead (the cmds in Dockerfile should be in Json format)-

FROM Ubuntu

ENTRYPOINT ["sleep"]

CMD ["5"]

The CMD will get appended to ENTRYPOINT, else with the cmd line arg, if specified.

docker run --entrypoint blah ubuntu 10 : to override default entrypoint

Docker networking


When installed docker, it creates 3 networks automatically -

Bridge: the default network a container gets attached to (private + internal). Usually in range of 172.17.x.y
None: container not attached to any network; no connection to external host or other containers, they'll run in completely isolated network
Host: connect directly to the host network


docker run Ubuntu --network=none : Can specify a different network


To access the containers externally -

Either port map from container to host
OR run the container on host network: docker run Ubuntu --network=host

No network isolation left
Now we can access it on same port directly
BUT can't use the same port for same another container - unlike before


By default docker only creates 1 internal bridge network. We can create more and group containers -


Command
Description


docker network create --driver bridge --subnet 182.18.0.0/16 custom-iso-net
to create a new bridge network


docker network ls
to list all networks


docker inspect name/ID
to check a container's IP, mac, subnet, etc.


Docker has a built-in DNS server that helps the containers to resolve each other using the container name

This DNS server always runs at - 127.0.0.11


Docker uses network namespaces that creates a separate namespace for each container. It then uses virtual ethernet to connect containers together.


Docker Storage


Command
Description


/var/lib/docker
location in file system where docker store its data


docker volume create data_vol
create a volume for persistence storage in /var/lib/docker/data_vol


docker run -v data_vol:/var/lib/mysql mysql
to mount the vol in the container


docker run --mount type=bind,source=~/Desktop/data,target=/var/lib/mysql mysql
Using -v is old style, use this instead


volume mount mounts from volume dir in /var/lib/docker while bind mount mounts from any dir

Topics Uncovered


Topic name
Cheatsheet Link


Docker-Compose
link


Docker-Swarm
link


Other Docker Cheatsheets


Link 1
Link 2
Link 3
Link 4
Command	Description
`docker version`	to check the version of docker installed
`docker run nginx`	to start a container of nginx from image (if already exist, else it will pull from hub)
`docker run --name myserver nginx`	to start a container of nginx with a name
`docker ps`	list all running containers
`docker ps -a`	to list all containers - currently running as well stopped ones
`docker stop containerID/name`	to stop a running container provide either name or ID (first few letter works as long as it unique)
`docker rm containerID/name`	to remove a container permanently
`docker rm -f containerID/name`	to remove a running container permanently
`docker images`	to see a list of available images
`docker rmi name`	to delete a docker image
`docker pull nginx`	to only pull the docker image and not run the container
`docker exec ubuntu cat /etc/passwd`	to execute command in a container
`docker run -d ubuntu:latest`	to run and detach a container
`docker attach ID/name`	to attach back to the running container
`docker cp nginx:file.txt data/`	to copy a file from container to host [`cp container:source target`] (just like `scp`)
`docker cp data.txt nginx:file.txt`	to copy a file from host to container [`cp target container:source`]
Command	Description
`docker run redis:4.0`	to run a container with a different version, specify with `name:tag` format (will take latest tag by default)
`docker run -i name`	to run in interactive mode (by default won't take input from STDIN)
`docker run -it name`	to attach a psuedo terminal to the container
`docker run -p 69:3306 mysql`	to map the port 69 of localhost/dockerhost to port 3306 of the container running mysql (-p HOST:CONTAINER)
`docker run -P mysql`	to map all ports
`docker run -v /opt/datadir:/var/lib/mysql`	to persist the data : map a dir outside the container on docker host to a dir inside the container (-v HOST:CONTAINER)
`docker inspect name/ID`	to inspect a container (output JSON)
`docker logs name/ID`	to view logs of a container
`docker stats`	to view stats of running containers
`docker top name/ID`	to view processes of a container
Command	Description
`docker run -e BG_COLOR=blue simple-webapp-color`	to set the environment variable for our container
`docker inspect name/ID`	to find the env var in a running container, refer to `config` section in output
Command	Description
`docker build Dockerfile -t webserver/release-one`	to build a docker image with a Dockerfile and give it a tag
`docker tag Ubuntu Ubuntu:20.04`	to tag an image
`docker build .`	build an image from Dockerfile in current directory
`docker save nginx > nginx.tar`	save an image to tar file
`docker load -i nginx.tar`	load an image from tar file
`docker push webserver/release-one`	to host it on docker hub community (docker registry)
Command	Description
`docker network create --driver bridge --subnet 182.18.0.0/16 custom-iso-net`	to create a new bridge network
`docker network ls`	to list all networks
`docker inspect name/ID`	to check a container's IP, mac, subnet, etc.
Command	Description
`/var/lib/docker`	location in file system where docker store its data
`docker volume create data_vol`	create a volume for persistence storage in `/var/lib/docker/data_vol`
`docker run -v data_vol:/var/lib/mysql mysql`	to mount the vol in the container
`docker run --mount type=bind,source=~/Desktop/data,target=/var/lib/mysql mysql`	Using `-v` is old style, use this instead