<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _resource_prefix(self, resource=None):
 """Get elastic prefix for given resource. Resource can specify ``elastic_prefix`` which behaves same like ``mongo_prefix``. """

        px = 'ELASTICSEARCH'
        if resource and config.DOMAIN[resource].get('elastic_prefix'):
            px = config.DOMAIN[resource].get('elastic_prefix')
        return px