Let's start with the app.yml file under src/main/docker inside your gateway application.
As we saw at the beginning of the chapter, the file starts with the Docker version that it supports:
version: '2'
This is followed by the services section where we define the various services, applications, or components that we will kick start with this Docker file.
Under services section, we will define a name for the service, in our case we have used gateway-app, followed by the image that we want to use as a container. This image is generated with the help of the Docker file that we have in that folder.
This is followed by the series of environment variables that our application will depend on, they include:
