title: How to force postgres docker container to start with new DB
body: <p>I have a docker compose file that looks like:</p>
  
  <pre>
  version: "3"
  services:
      redis:
          image: 'redis:3.2.7'
          # command: redis-server --requirepass redispass
  
      postgres:
          image: postgres:9.6
          ports:
              - "5432:5432"
          environment:
              - POSTGRES_USER=airflow
              - POSTGRES_PASSWORD=airflow
              - POSTGRES_DB=airflow
  #            - PGDATA=/var/lib/postgresql/data
  
  
      webserver:
          image: airflow:develop
          depends_on:
              - postgres
  
          ports:
              - "8080:8080"
  
          command:
              - webserver
  </pre>
  
  <p>After I run <code>docker-compose up</code> I see all the services started and seemingly working well. My <code>webserver</code> service connects to postgres with the following sqlalchemy connection string: <code>postgresql+psycopg2://airflow:airflow@postgres/airflow</code></p>
  
  <p>Whenever I kill the composition (with <code>ctrl-c</code> or <code>docker-compose stop</code>) and then restart it, the data in postgres seems to persist. The reason I believe it persists is because my webserver starts with data from the previous session. </p>
  
  <p>I read the docs for the <a href="https://hub.docker.com/_/postgres/" rel="nofollow noreferrer">postgres docker image</a> and found the <code>PGDATA</code> environment variable. I tried to force set it to the default (as seen in the commented line in my docker compose file, but that didn't help. I'm not sure how else to debug why data seems to be persisting between container starts. </p>
  
  <p>How can I force my postgres container to start fresh with each new initialization?</p>