Why do you think chat service needs Firebase function? Usually we made it by only Firebase database. The answer is as follows. If you make chat service by using only firebase database , We can not take a Push notification The database server becomes heavy It can be only useful when a partner connects at the same time. So we should use firebase function for send message notification to partner and save messages in local database(sqlite, realm). And firebase database is only used for saving partner's info (uid, name.. etc) and last message info ( message, timestamp.. etc). And.. Let's make simple chat service by Firebase function. 1. Update chat message to Firebase database last_id : last user id sending message. u_id : my unique id last_word : last message in this chatting room. 2. Link Firebase database and Firebase Function /u_data/{u_id}/last_message/{room_id} is database reference tree directory This function i...