I use port forwarding if I want to access my local server NodeMCU from internet. However if I use IOT platforms like Blynk, ThingSpeak... then I dont need to care about port forwarding. We can access our device easily using their auth token and URL provided.
So how do these platforms communicate with the NodeMCU? And how can I implement such connection? I am not asking to know/implement the entire IOT cloud platform, I am just curious understand the way they communicate without port forwarding.
It will be very helpful if you share any tutorial link to implement such server.