docker-zabbix-server/frontend/zabbix.conf.php

<?php
// Zabbix GUI configuration file.
global $DB;

$DB['TYPE']     = 'POSTGRESQL';
$DB['SERVER']   = 'POSTGRES_HOST';
$DB['PORT']     = '0';
$DB['DATABASE'] = 'POSTGRES_DB';
$DB['USER']     = 'POSTGRES_USER';
$DB['PASSWORD'] = 'POSTGRES_PASSWORD';

// Schema name. Used for IBM DB2 and PostgreSQL.
$DB['SCHEMA'] = '';

$ZBX_SERVER      = 'ZABBIX_HOST';
$ZBX_SERVER_PORT = 'ZABBIX_PORT';
$ZBX_SERVER_NAME = '';

$IMAGE_FORMAT_DEFAULT = IMAGE_FORMAT_PNG;