Scenario
IoT device (currently IPv4 device) that sends via TCP socket a payload to a server once per day. The server has a public IP address, the device is behind a router/NAT. I'm going to use a module based upon ESP8266 (i.e. Olimex one)
Goal
The server should be able to send data to any client whenever it needs to.
I'm no interested in direct client-to-client communication (i.e. connect to a device from my smartphone) like the hole punching is supposed to do.
Other requirements
The IoT devices might grow up to several thousands. Their Internet connection is provided by many 4G-enabled routers/modems. Each one will handle 10-20 clients.
Proposed solution
As far as I understand a common solution is MQTT. The clients periodically send data to the broker (i.e. Mosquitto running on the hosting server), that in turn updates the main web app that runs on the same server.
Question
Does theIs MQTT approach is suitable for a "large" number of devices (1000+) most of them behind a 4G router?