AWS_ACCESS_KEY_ID

AWS_SECRET_ACCESS_KEY

AWS_DEFAULT_REGION

INTERNAL_IP

IP_PORT

SWARM_TOKEN

BUCKET

DIGITAL_OCEAN_TOKEN

Gain insights into Docker architecture, images, and containers. Delve into Docker Compose, JS integration, and production readiness. Master deploying, clustering, and scaling Rails apps using Docker tools.

tarball.tar.gz

simpleJob

simpleJob2

simpleJob-copy

viewImages

dockerCompose1

challenge1

dockerComposeRedis1

dockerComposeRedis2

dockerComposeRedis3

cdToUsercode

delGitCopyUpCreate

delGitCopyUp

delGitCopyUpMigrate

webPackerCh7

RSpec-Ch8

RSpec-Ch8_2

RSpec-Ch8_2_1

RSpec-Ch8_3

runRailsUsingCustomImage

dockerCompose1-copy

RSpec-Ch8_2-copy

delGitCopyUp-copy

RSpec-Ch8_5

RSpec-Ch8_6

RSpec-Ch8_6_GUI

dockerCompose1-copy-copy

dockerComposePostgres1

webPackerCh7-copy

postgress_last_lesson

Ch12_2

postgress_2nd_last_lesson

Ch12_3

gem_1

gem_2

irritation_1

irritation_1_1

Ch12_1

webPackerCh7_2

Cloud

Cloud_DO

Cloud_1

Cloud_2_1

Cloud_2_2

Cloud_2_4

RSpec-Ch8_2_new

RSpec-Ch8_7

Cloud_1_1_bucket

dockerComposeRedis3-copy

dockerComposeRedis2-copy

Cloud_DO_2

chap4_1

chap5_3

chap5_4

challenge

simpleJob2-ForceRelaunch

simpleJob-ForceRelaunch

RSpec-Ch8_5-copy

dockerCompose1-copy-copy-copy

testing

chap4_1-copy

chap5_3-copy

chap5_4-copy

dockerComposeRedis3-copy-iwrz0a

postgress_2nd_last_lesson-copy

postgress_last_lesson-copy

webPackerCh7_2-copy

This course is your field manual for building Rails applications with Docker. 

To kick things off, you’ll start by learning the basics of Docker like architecture, images, and containers. You will then be introduced to Docker Compose and use it to build up to a multiservice application with Redis.

You will then work to get your Dockerized setup to play nice with JavaScript, using both the standard asset pipeline and webpacker, Rails’ newest approach for integrating modern JavaScript front ends.

Lastly, you will learn how to prepare your Rails app for production. Once ready, using Docker’s own tools, you will provision machines, create a cluster, deploy the app, and scale the app’s resources to meet its changing needs.

By the end of the course, you will be able to confidently use Docker in any of your further projects.

Docker for Rails Developers

# Modifying Dockerfile
Currently, every time we want to start a Rails server in a container, we have to explicitly specify the command `bin/rails s -b 0.0.0.0` as part of our `docker run` command. This is a problem because the main purpose of our custom image is to start a Rails server. It would be better if we could embed the knowledge of how to start the Rails server in the image itself. 

## `CMD` instruction
We can do this by adding a new instruction to our Dockerfile. The `CMD` instruction “command,” specifies the default command to run when a container is started from the image. Let’s use this in our Dockerfile to start the Rails server by default: 
```text
CMD ["bin/rails", "s", "-b", "0.0.0.0"] 
```
Looking at this new line, you may notice the weird array notation used to specify the command. This form, which is known as the **Exec form** is needed so that our Rails server is started as the first process in the container and correctly receives **Unix** signals, such as the signal to terminate. It is the recommended form and also the most commonly used. 
 
The other form of the `CMD` instruction, which is rarely used, omits the array notation in favor of writing the command directly: 
```text
CMD bin/rails s -b 0.0.0.0 
```
This is known as the **Shell form** because Docker executes the command via a command shell, prefixing it with **/bin/sh -c**, so in our case, it runs `/bin/sh -c bin/rails s -b 0.0.0.0`. The problem is that **/bin/sh -c**, rather than the Rails server, is the first process inside the container; since **/bin/sh -c** does not pass signals on to its subprocesses, this would cause issues when trying to terminate the server. Generally, you can just avoid this form altogether. 

# Running modified Dockerfile
Now, let’s rebuild our image with our new `CMD` instruction. The new image built using this Dockerfile will help us launch the Rails server by omitting the `bin/rails s -b 0.0.0.0`. 

It’s important to note that the `CMD` instruction just provides a default command. You can specify a different one when you issue the `docker run` command. 

For example, to list our Rake tasks, we would run the following command. You can try it out in the terminal after running `Ctrl+C`. 
```text
$ docker run --rm railsapp bin/rails -T
```

## 🍀 Practice
Try to do the following:

1. Edit the Dockerfile by adding `CMD` instruction.

2. Click the Run button.

3. Build the `image` named **railsapp**.

4. Launch the Rails server, omitting the
`bin/rails s -b 0.0.0.0`.

5. Click the URL to view the default Rails page.

6. Exit the bash shell.

7. Run the Rake task.

>**Reminder:** The image building will take time (around 10–12 minutes). In case the terminal gets disconnected, click the Run button again. 



We will learn to modify the Dockerfile according to our requirements.

A Default Command

Introduction

A Brave New World

Running a Rails App in a Container

Fine-Tuning Our Rails Image

Describing Our App Declaratively with Docker Compose

Beyond the App: Adding Redis

Docker for Rails Developer—Exam 1

Adding a Database: Postgres

Playing Nice with JavaScript

Testing in a Dockerized Environment

Advanced Gem Management

Some Minor Irritations

Docker for Rails Developer—Exam 2

The Production Landscape

Preparing for Production

A Production-Like Playground

Deploying to the Cloud

Docker for Rails Developer - Exam 3

Closing Thoughts and Next Steps

APPENDIX

A Default Command

Modifying Dockerfile