docker-compose不会覆盖dockerfile环境变量

我试图从我的docker-compose设置基本的postgres信息.容器启动但是当我运行docker-compose时,不会覆盖来自Dockerfile的变量.请帮忙.

FROM mine/debian7

## START: UPDATES & INSTALLS ###########################################################################################
RUN echo "deb http://apt.postgresql.org/pub/repos/apt/ wheezy-pgdg main" >> /etc/apt/sources.list.d/pgdg.list && 
    wget --quiet -O - http://apt.postgresql.org/pub/repos/apt/ACCC4CF8.asc | apt-key add -  && 
    apt-get update && 
    apt-get upgrade && 
    apt-get install -y python-software-properties software-properties-common postgresql-9.4 postgresql-client-9.4 postgresql-contrib-9.4 && 
    apt-get clean && 
    rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
## END: UPDATES & INSTALLS #############################################################################################

ENV DB_USER_NAME test
ENV DB_PASSWORD test
ENV DB_NAME test

## START: CONCFIGURATION ###############################################################################################
# start postgres at boot
#RUN     echo "/etc/init.d/postgresql start" >> ~/.bashrc
USER    postgres
RUN /etc/init.d/postgresql start && 
    psql --command "CREATE USER $DB_USER_NAME WITH SUPERUSER PASSWORD '$DB_PASSWORD';" && 
    createdb -O $DB_NAME $DB_NAME
RUN     echo "host all  all    0.0.0.0/0  md5" >> /etc/postgresql/9.4/main/pg_hba.conf
RUN     echo "listen_addresses='*'" >> /etc/postgresql/9.4/main/postgresql.conf
VOLUME  ["/etc/postgresql","/var/log/postgresql","/var/lib/postgresql"]
#USER root
#RUN update-rc.d postgresql defaults
## END: CONCFIGURATION #################################################################################################


EXPOSE 5432

CMD service postgresql start && tail -f /var/log/postgresql/postgresql-9.4-main.log

还有我的docker-compose文件：

tomcat:
  image: clegge/tomcat
  ports:
    - "8080:8080"
  volumes:
    - sample.war:/opt/tomcat7/webapps/sample.war

postgres:
  build: /Users/clegge/Dockers/docker-postgres-base/
  ports:
    - "5432:5432"
  stdin_open: true
  tty: true
  environment:
   - DB_USER_NAME=legge_crud
   - DB_PASSWORD=legge_crud
   - DB_NAME=test

我错过了什么？