In this step, we define a default value, "db", for the InfluxDB host the api needs to connect to.
// Create a client towards InfluxDB
let influx = new Influx.InfluxDB({
host: process.env.INFLUXDB_HOST || "db",
database: 'iot'
});
As each service of a Docker Compose application can communicate with other services using their name, this code changes replaces the environment variable that would be defined in the docker-compose.yml file otherwise.