How do I pass environment variables to Docker containers

Question

I'm new to Docker, and not clear about how to access an external database from a container. Can I just hard-code in the connection string?

# Dockerfile
ENV DATABASE_URL amazon:rds/connection?string

Answer 1

You can pass environment variables to your containers with the -e flag.

Ex-

sudo docker run -d -t -i -e REDIS_NAMESPACE='staging' \ 
-e POSTGRES_ENV_POSTGRES_PASSWORD='foo' \
-e POSTGRES_ENV_POSTGRES_USER='bar' \
-e POSTGRES_ENV_DB_NAME='mysite_staging' \
-e POSTGRES_PORT_5432_TCP_ADDR='docker-db-1.hidden.us-east-1.rds.amazonaws.com' \
-e SITE_URL='staging.mysite.com' \
-p 80:80 \
--link redis:redis \  

--name container_name dockerhub_id/image_name