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16_simple_ruby_image.md

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Create An Image for a Ruby Application

Docker Documentation References:

Dockerfile

docker build

docker run

docker images

docker rmi

Other Documentation References:

Ruby Language

Intent

The purpose of this kata is to familiarize yourself with the process of creating the simplest possible image for running a ruby application.

Overivew

In this exercise we will create a simple Ruby application and place it in a Docker Image. We will then run that image. When we are done we will remove the image and its associated containers.

Kata Steps

Create a Ruby Application

Command:

Create a directory for called rbcode and cd into it

mkdir rbcode && cd rbcode

Use an editor to create a file named hello_world.rb, or use the file contained in this repository

The file should contain the following code

puts 'Hello World'

Test the application

Command

ruby hello_world.rb

Output

thought:DockerKata rich$ ruby hello_world.rb
Hello World

Create a Dockerfile

Use an editor to create a file name ruby_hello_world_Dockerfile, or copy the ruby_hello_world_Dockerfile from this repository.

The file should contian the following

FROM ruby:alpine
MAINTAINER [email protected]

COPY hello_world.rb /

ENTRYPOINT [ "ruby", "hello_world.rb" ]

Build the Image

Command

docker build -f ruby_hello_world_Dockerfile .

Output

thought:DockerKata rich$ docker build -f ruby_hello_world_Dockerfile .
Sending build context to Docker daemon 410.1 kB
Step 1/4 : FROM ruby:alpine
alpine: Pulling from library/ruby
79650cf9cc01: Pull complete
6ed882a02057: Pull complete
7285d5575114: Pull complete
d441eef8a308: Pull complete
25cbb501c00e: Pull complete
Digest: sha256:ead6b812ae745761a90c8900eae672b8d7e952e3464a92f3e977b073e4f91f1a
Status: Downloaded newer image for ruby:alpine
 ---> 3db0e32b7207
Step 2/4 : MAINTAINER [email protected]
 ---> Running in a7d7ed8af293
 ---> aacee134dc3b
Removing intermediate container a7d7ed8af293
Step 3/4 : COPY hello_world.rb /
 ---> 12ea97af7522
Removing intermediate container d114cf088595
Step 4/4 : ENTRYPOINT ruby hello_world.rb
 ---> Running in 00365bcc4a46
 ---> cc70f6402870
Removing intermediate container 00365bcc4a46
Successfully built cc70f6402870

List Images

Command

docker images

Output

thought:DockerKata rich$ docker images
REPOSITORY                                   TAG                 IMAGE ID            CREATED             SIZE
<none>                                       <none>              cc70f6402870        54 seconds ago      61.2 MB

Note: We will use the IMAGE ID which will differ from machine to machine, so you must select what is on your computer for the next two steps.

Run the Image

Command

docker run 167b6bbcdc92

Output

thought:DockerKata rich$ docker run cc70f6402870
Hello World

Change Directory Back to the root dir

Command

cd ..

Delete the Image (and related container)

Command

docker rmi -f cc70f6402870

Output

thought:DockerKata rich$ docker rmi -f cc70f6402870
Deleted: sha256:cc70f64028700dbd0fbe46c37ee5b33b7933abd0c6220fed840169c65d0a8a5e
Deleted: sha256:12ea97af75224f4e63decc5ef01c6bf231730aa608b9d01ebca9f3a4eb801c3b
Deleted: sha256:aacee134dc3be0bd28b98f1742278c667c34310f9d43cd254d98143f1d1b37bd

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