Docker Cheatsheet for Web Devs

As a web-dev in the microservices era you will encounter Docker sooner than later. It's always good to have the essential commands at arm's reach. Following is a list of Essential Docker commands that have helped me on a daily basis, hope this helps yo too. Happy Hacking!

Docker Commands

Docker run command

docker run <image-name>

example
docker run hello-world

To add a override command

docker run <image-name> <default command override>

example

docker run busybox ls

List all the running containers

Docker ps command specifically shows running containers

docker ps

Show all container ever run on machine

docker ps --all

Docker ps is also used to get the ID of coantainer

docker run = docker create + docker start

when we create container we just prep it with say file sysytem etc
When we run the container then we provide the default command that runs the program

docker create hello-world

now we use the id to start

docker start -a 3c8a5bb0fe7153955d1261054e5b4c99f757920f7760fa7c07803cdbee4b36c1

-a argument watches for any output and prints it on terminal

To re-run an exitied container

first we get the conatiner of ID with ps command

docker ps --all

Then use the id with start command

docker start -a 1285b5630516

When we re-run / restart a container we cannot replace the default command, it automatically takes the default command on re-run with commond it was created with.

Removing stopped containers

docker system prune

Docker logs command

Docker logs command shows all the output of con tainer when it had been running

docker logs 73e564097bd5e6689c2bc5687c038dca99ec77d8716f7ff9eeab9434d422bb8d

Stopping a running container

docker stop <container-id>

This sends a SIGTERM signal allowing container to shut down in some time usually 10s, after that it issues Docker kill anyway

docker kill <container-id>

This command issues a SIGKILL that immediately stops the container

Docker stop is better way to stop*

Executing commands in running containers

docker exec -it <container-id> <command>

exec command allows us to type extra commands
it flag helps us to enter text and send it to container

The it flag

its a -i and -t
i attaches our terminal to STDIN
t flag makes sure that it shows the output formatted on terminal, like auto complete you see with redis-cli

How to get shell access in docker container

sh is command processor like bash, zsh etc

docker exec -it <container-id> sh

if ctrl + c doesnt help you exit use ctrl+d or just type exit

starting container with a shell

docker run -it <container-name> sh

Creating a Docker image

Flow to Creating a DockerFile

specify base image
Run some commands to install additional programs
specify command to run on container startup

Sample docker file to create redis image

Create a file named Dockerfile no extension just Dockerfile

# Use an existing docker image as base 
FROM alpine


# Download and install a dependency
RUN apk add --update redis

# Tell the image what to do when it starts as a container
CMD ["redis-server"]