Gitlab ci, symfony + postgres Error Connection refused

I have an error when I create the schema with doctine

$ php bin/console doctrine:schema:create --env=test

In AbstractPostgreSQLDriver.php line 73:

  An exception occurred in driver: SQLSTATE[08006] [7] could not connect to s  
  erver: Connection refused                                                    
    Is the server running on host "127.0.0.1" and accepting                     
    TCP/IP connections on port 5432?      

with my gitlab-ci.yml

database:
  stage: building
  services:
    - postgres:10
  variables:
    POSTGRES_DB: back
    POSTGRES_USER: postgres
    POSTGRES_PASSWORD: ''
    POSTGRES_HOST: postgres
    POSTGRES_PORT: 5432
  before_script:
    # Install pdo_pgsql driver
    - apt-get update
    - apt-get install -y libpq-dev
    - docker-php-ext-install pdo_pgsql
  script:
    - php bin/console doctrine:schema:create --env=test
    - php -d memory_limit=2048M bin/console --env=test cache:warmup --no-debug

And my gitlab-parameters.yml (who is cp on app/config/parameters.yml)

parameters:
    database_host: postgres
    database_port: 5432
    database_name: back
    database_user: postgres
    database_password: ''

Other information :

when I try to create database, I have the good message from gitlab-ci

$ php bin/console doctrine:database:create --env=test
Could not create database "back" for connection named default
An exception occurred while executing 'CREATE DATABASE "back"':

SQLSTATE[42P04]: Duplicate database: 7 ERROR:  database "back" already exists

How fix it?