Docker and Containers - Docker Intro Lab

This lab demonstrates 3 ways of running docker containers, how to package a Docker image using Dockerfile, and how to use “bind mount” to map a host directory inside container.

Learning Outcomes

• How to use container to run a single task
• How to run container interactively
• How to run container in background
• How to package a Docker image and run a container upon it
• How to bind mount a host directory to container

Prerequisites

• Docker ID, register one here if you don’t have it

Operations

0: Preparations

• Clone the demo git repository

git clone https://github.com/dockersamples/linux_tweet_app

• Export an environment variable containing your DockerID

export DOCKERID=<your docker id>

1: Run some simple Docker containers

1.0: To run a single task

This could be a shell script or a custom app.

docker container run alpine hostname

This creates a container from image alpine:latest and run hostname process inside, when the process exits, the container stops, but the resources are not deleted, to look up,

docker container ls --all

1.1: Interactively

This connects you to the container similar to the way you SSH into a remote server.

docker container run --interactive --tty --rm ubuntu bash

• —interactive says you want an interactive session.
• —tty allocates a pseudo-tty.
• —rm tells Docker to go ahead and remove the container when it’s done executing.
• run bash as main process in Ubuntu container

Docker has attached to the shell in the container, relaying input and output between your local session and the shell session in the container.

1.2: In the background

For long-running services like websites and databases.

 docker container run \
 --detach \
 --name mydb \
 -e MYSQL_ROOT_PASSWORD=my-secret-pw \
 mysql:latest

• —detach will run the container in the background.
• —name will name it mydb.
• -e will use an environment variable to specify the root password

This runs a MySQL container with the specifications above.

To run a command inside the container,

docker exec -it mydb \
 mysql --user=root --password=$MYSQL_ROOT_PASSWORD --version

To connect to a new shell process inside an already-running container,

docker exec -it mydb sh

2: Package and run a custom app using Docker

In this task, we’re going to create a simple NGINX website from a Dockerfile.

• To see the Dockerfile

cd ~/linux_tweet_app
cat Dockerfile

• To create a new Docker image using the instructions in the Dockerfile

  • —tag allows us to give the image a custom name. In this case it’s comprised of our DockerID, the application name, and a version. Having the Docker ID attached to the name will allow us to store it on Docker Hub in a later step
  • . tells Docker to use the current directory as the build context

docker image build --tag $DOCKERID/linux_tweet_app:1.0 .

• To start a new container from the image you created

 docker container run \
 --detach \
 --publish 80:80 \
 --name linux_tweet_app \
 $DOCKERID/linux_tweet_app:1.0

Any external traffic coming into the server on port 80 will now be directed into the container on port 80. The format of the —publish flag is host_port:container_port.

• To shut it down and remove it

docker container rm --force linux_tweet_app

3: Modify a running website

When you use a bind mount, a file or directory on the host machine is mounted into a container running on the same host. This will allow any changes made to the files on the host to be immediately reflected in the container, however, this will not change the underlying image.

docker container run \
 --detach \
 --publish 80:80 \
 --name linux_tweet_app \
 --mount type=bind,source="$(pwd)",target=/usr/share/nginx/html \
 $DOCKERID/linux_tweet_app:1.0

Use the —mount flag to mount the current directory on the host into /usr/share/nginx/html inside the container

Then make a change to the index page, the change will take effect immediately,

cp index-new.html index.html

Official Links

Lab: Docker Intro

Written by Warren who studies distributed systems at George Washington University. You might wanna follow him on Github