Starting a Redis Server
We will add redis image in our docker-compose.yml and run Compose.
We'll cover the following...
Why Redis? 
What we have learned so far is not enough to build anything other than the most basic websites or apps. We are missing a key piece of the puzzle: how to connect our Rails app to external services like a database. Here, we will learn how to do just that, starting with
Why Redis before a database?
Because, while the process of adding services to our app is similar, it turns out that Redis is easier to integrate into our app than a database. In fact, this will teach you the basic skills needed to add any service to your app, be it a database, background workers, Elasticsearch, or even a separate JavaScript front end. Soon our Docker-fueled apps will be every bit as powerful as we are used to, and then some.
Starting a Redis server
We want our Rails app to talk to Redis. First, we are going to need a Redis server that our application can talk to. As you might ...