This is a web application sample which is dockerized. This app uses postgres as its backend storage.
In the world of Docker, we usually take advantage of `link` to connect containers.
Therefore, in golang-postgres-web-sample, we use the following environment to connect postgres.
*POSTGRES_PORT_5432_TCP_ADDR*: postgres host address
*POSTGRES_PORT_5432_TCP_PORT*: postgres host port
*USERNAME*: postgres username
*PASSWORD*: postgres password
*INSTANCE_NAME*: postgres dbname