Docker Workshop | karankapoor.in

This is a very basic, 20 minute quick guide to running your first docker container running an application.

Prerequisites

Docker desktop downloaded and installed on your machine.
Git command line downloaded and installed on your machine
A github user account (optional)
A docker hub account

Verify your installation

Start the docker service on your machine and check the docker version.
```
 docker -v
```
Run your first hello world container
```
 docker run --name hello hello-world
```

Playing with your installation

Ok, so your container can say hello, can you run some other commands inside it?
```
 docker run busybox uptime
```

Don’t try this at ‘host’

So, if it’s an OS, can I log into it on the command line and actually do stuff? Sure!!
```
 docker run -it busybox sh
```
Now try
```
 whoami
```
Surprise surprise!! You’re root!! But wait, if I’m root now, can’t I do anything? I mean ANYTHING !! Let’s try something crazy!!

PS: Make sure you’re still inside the container, you DON’T want to do this on your machine.
```
 ls 
 uptime
 # ok, so commands work! Also..
 # I see bin.. evil laugh.. let me wreak havoc, and delete it!! I'm ROOT!!
 rm -rf bin
 # and now..
 ls
 uptime
 # Honey I blew up the machine!! Did I break my host machine too?
 exit
```
However, once outside of the container, try ls and uptime again (if you’re on a linux/ mac that is..), and they’re still working..

Voila! Docker isolation in action!!

Serving a static webpage

I have an html page, and I want to serve it using an nginx server..

 # Creating an simple webpage that says Hello!!
 echo <html><head></head><body>Hello!!</body></html> > index.html

 # Installing and enabling an httpd server in one single command
 docker run -dit --name my-web-server -p 8080:80 -v "$PWD":/usr/local/apache2/htdocs/ httpd:2.4

 # Launch your browser and check your machine's port 8080 (mac/ linux)
 open "http://localhost:8080"   # for mac
 explorer "http://localhost:8080"   # for windows

Cleanup running containers

 docker ps 

 # Notice the status of the container named my-web-server. Stop it
 docker stop my-web-server

 # Remove the container
 docker container rm my-web-server

Dockerizing a node.js app

Let’s now do something a little more real world!! Let’s get our hands on a very simple node app, create a docker container for it, push it to a repo, and learn how to pull and run it.

 git clone https://github.com/karan-kapoor90/docker-workshop.git

 # consider running the application locally if you have node installed on your machine
 npm install
 node index.js
 # But the happy scenario, in case you don't have nodejs installed on your machine, docker to the rescue

Explore the code.. as a shortcut, consider reading the readme file on the git repository.
Build a docker container for your code. PS: The following step creates a docker image which
- Is based on a nodejs base image
- Takes a copy of your code’s dependencies (that’s the package.json file for a nodejs app)
- Downloads all those dependencies into a folder
- Copies your code into the same folder
- Declares the command that is used to run your code (node index.js in this case.)
PS: My dockerhub username is karankapoor
```
 export DOCKER_USERNAME=<your-dockerhub-username>
 # building your container locally
 docker build -t $DOCKER_USERNAME/docker-workshop:latest -f Dockerfile .
```
All the steps defined above, and more, such as setting environment variables, creating an image that depends on the output of multiple such images (aka multistage images) etc., is all defined in the Dockerfile file in the code you just checked out from github.

Run the container locally, exposing the app on port 30000 of your local host machine

docker run -d -p 30000:3000 --name my-app $DOCKER_USERNAME/docker-workshop:latest

# inspect the docker container running in the background
docker ps

Explore your shiny new docker app in the browser

http://localhost:30000/
http://localhost:30000/welcome.html
http://localhost:30000/hello   # a GET endpoint that responds with some JSON content

Clean up

docker container stop $(docker container ls -aq)   # Stop all running containers

Pushing your first image to dockerhub

Your first container for the world to see

docker login   # it will ask you for your docker registry credentials. Since we're using dockerhub, no need to provide a registry URL
docker push $DOCKER_USERNAME/docker-workshop:latest   # this will push your docker container to docker hub, kind of like a github for docker containers.

Now you’re a champ! But why stop here? If you installed docker desktop for your platform, most likely, you also have a local distribution of kubernetes running on your machine.

For more info on why you should consider orchestrating your container using kubernetes, and a basic how-to, follow the guide here.