Docker-compose in action

In the last lesson, we successfully added the database to our app.

You can clone the project using git clone https://github.com/venky8283/Docker.git

Type git checkout 4de325cf1da2428e757be4f2bcc53f35c384c598 to get to the code used in this lesson.

Summary of steps to add a database

1. Pull a Docker image of MySQL server
2. Create a SQL init script for the database
3. Run the database container with environment variables
4. Mount the init.sql script in the docker-entrypoint-init.db folder
5. Modify the code and rerun app container with a link to the database container

Every time you want to rerun the app, you have to go through these steps. Wouldn’t it be great if we could automate these steps?

The good news is docker-compose addresses this issue and automates these steps. In short, Compose is a tool for defining and running multi-container Docker applications.

Docker-compose installation

Follow the steps below to install docker-compose or check out the official installation for all platforms.

Windows and Mac

If you have installed Docker desktop, then docker-compose already comes with it. You can verify it using docker-compose --version.

Linux

Type the following commands in the terminal step by step:

• Run this command to download the current stable release of Docker Compose sudo curl -L "https://github.com/docker/compose/releases/download/1.25.4/docker-compose-$(uname -s)-$(uname -m)" -o /usr/local/bin/docker-compose

• Apply executable permissions to the binary with sudo chmod +x /usr/local/bin/docker-compose

• Verify installation with docker-compose --version.

Docker-compose file

Let’s create a docker-compose file and see if we can automate this.

If you checkout to commit “Docker-compose file for the app”, you will see a docker-compose file there.

Modify mounts according to your files system. For example,

volumes:
 - "/usercode/:/code"

Here, replace ‘usercode’ directory to your directory where the project is cloned. It can be something like /Users/Home/username/documents/Docker.

Then, open up the terminal and cd into the directory where docker-compose.yml file is present.

Finally, hit docker-compose up --build.

You can also try running the code below. We will look at the commands in detail in the next lesson.

After a couple of minutes and a lot of steps, you will see that your app is running at 0.0.0.0:5000 with a database attached to it.