Demo Sinatra Dockerize

Instructions on how to Dockerize a simple Sinatra application

Table of Contents

• Build the docker image
  • Create the Dockerfile
  • Build and run the container
• Some useful commands
  • Docker image
  • Docker container

Build the docker image

Create the Dockerfile

A Dockerfile is a text file that contains all the commands to builds an image. Docker can build images automatically by reading the instructions from a Dockerfile.

Navigate to the root directory and create the file.

$ touch Dockerfile

Docker provides official Ruby images and we are going to use Version 2.6.5 as our parent image.

Open Dockerfile and add the following lines:

# create a layer from the Ruby 2.6.5 Docker image
FROM ruby:2.6.5-stretch

# install the GNU C compiler and GNU C++ compiler
RUN apt-get update -qq && apt-get install -y build-essential

# set up the directory for the build context
ENV APP_HOME /demo-sinatra-dockerize
RUN mkdir $APP_HOME
WORKDIR $APP_HOME

#add files from current directory
ADD Gemfile* $APP_HOME/
RUN bundle install --without development test

ADD . $APP_HOME

EXPOSE 4567

CMD ["bundle", "exec", "rackup", "--host", "0.0.0.0", "-p", "4567"]

For deployment purposes, we include the RUN bundle install --without development test line, as we don't need our development dependencies for that.

The EXPOSE instruction indicates the ports on which a container listens for connections. If there is a common, traditional port for your application, you should use it.

Execute the following command to see the most recently created images.

$ docker images

Build and run the container

Run the build command to build the image with the dockerfile.

$ docker build . -t demo-sinatra-dockerize

Whenenver you update the dockerfile, you need to run the command.

Now that we have our image, let’s run it!

$ docker run -p 4567:4567 demo-sinatra-dockerize

Go to http://localhost:4567/ to see it running.

Run the following command to see a list of running containers

$ docker ps

Some useful commands

Run a Hello-World image

Pull an exisiting Hello-World example image from Docker

$ docker image pull library/hello-world

or

$ docker image pull hello-world

Run the image as a container if pull the image if it does not exist.

$ docker container run hello-world

You will see the following message:

Hello from Docker!
This message shows that your installation appears to be working correctly.

To generate this message, Docker took the following steps:
 1. The Docker client contacted the Docker daemon.
 2. The Docker daemon pulled the "hello-world" image from the Docker Hub.
    (amd64)
 3. The Docker daemon created a new container from that image which runs the
    executable that produces the output you are currently reading.
 4. The Docker daemon streamed that output to the Docker client, which sent it
    to your terminal.

To try something more ambitious, you can run an Ubuntu container with:
 $ docker run -it ubuntu bash

Share images, automate workflows, and more with a free Docker ID:
 https://hub.docker.com/

For more examples and ideas, visit:
 https://docs.docker.com/get-started/

The hello-world container terminates automatically when you see the message above.

Docker image

List all images created

$ docker image ls

Remove one or more images

$ docker image rm [imageName]

Pull an image from Docker Hub

$ docker image pull [imageName]

Docker container

Pull a docker image as a container.

$ docker container run [imageName]