How to use environment variables in docker compose

Question

I would like to be able to use env variables inside docker-compose.yml, with values passed in at the time of docker-compose up. This is the example.

I am

Answer 1

When using environment variables for volumes you need:

1. create .env file in the same folder which contains docker-compose.yaml file

2. declare variable in the .env file:

   HOSTNAME=your_hostname
   

3. Change $hostname to ${HOSTNAME} at docker-compose.yaml file

   proxy:
     hostname: ${HOSTNAME}
     volumes:
       - /mnt/data/logs/${HOSTNAME}:/logs
       - /mnt/data/${HOSTNAME}:/data
   

Of course you can do that dynamically on each build like:

echo "HOSTNAME=your_hostname" > .env && sudo docker-compose up