protected function getDockerfileVariables()
    {
        // Merge service OS packages definition.
        if ($os_packages = $this->getInfoProperty('packages')) {
            $this->mergeConfigVariable('PACKAGE_INSTALL', $os_packages);
        }

        // Merge service PHP pecl packages definition.
        if ($pecl_packages = $this->getInfoProperty('pecl_packages')) {
            $this->mergeConfigVariable('PHP_PECL', $pecl_packages);
        }

        // Merge service PHP extensions definition.
        if ($php_extensions = $this->getInfoProperty('extensions')) {
            $this->mergeConfigVariable('PHP_EXT_INSTALL', $php_extensions);
        }

        // Merge service PHP docker command definition.
        if ($php_command = $this->getInfoProperty('commands')) {
            $this->mergeConfigVariable('PHP_COMMANDS', $php_command);
        }

        return $this->processDockerfileVariables();
    }